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Free Events and Activities

Mon-01 Aug | 08:00 – 10:00 | WB1
Kamide Lecture – IG

Speaker(s): Seogi KANG, Stanford University

Multi-scale Airborne Electromagnetic Imaging for Improved Understanding of Groundwater Systems
Mon-01 Aug | 08:00 – 10:00 | WB1
Distinguished Lecture – IG

Speaker(s): Chuan-Chou SHEN, National Taiwan University

Dating the Ancient Pacific Ruins of Coral Pyramids and Nan Madol
Mon-01 Aug | 08:00 – 10:00 | WB1
Section Meeting – IG
Mon-01 Aug | 11:00 – 12:30 | WB1
Opening & General Assembly
Mon-01 Aug | 16:30 – 18:30 | WB1
Kamide Lecture – PS

Speaker(s): Sae AIZAWA, Research Institute in Astrophysics and Planetology, Toulouse (IRAP)

Circulation and Escape of Planetary Ions at Mercury
Mon-01 Aug | 16:30 – 18:30 | WB1
Distinguished Lecture – PS

Speaker(s): Yong WEI, Institute of Geology and Geophysics, Chinese Academy of Sciences

Exploring Solar Wind Interaction With Planet Earth, Mars And Moon: From Global Pictures To Local Perspectives
Mon-01 Aug | 16:30 – 18:30 | WB1
Section Meeting – PS
Tue-02 Aug | 08:00 – 10:00 | WB2
Kamide Lecture – HS

Speaker(s): Zhenzhong ZENG, Southern University of Science and Technology

Biosphere-Atmosphere Interactions in Australia: Multiple Climate Equilibria
Tue-02 Aug | 08:00 – 10:00 | WB2
Distinguished Lecture – HS

Speaker(s): Deg-Hyo BAE, Sejong University

Meteohydrology: Hydrologic Modelling Techniques Using Weather Forecasting Information
Tue-02 Aug | 08:00 – 10:00 | WB2
Section Meeting – HS
Tue-02 Aug | 08:00 – 10:00 | WB1
Kamide Lecture – ST

Speaker(s): Lulu ZHAO, University of Michigan

Toward a Systematic Understanding and Forecasting of the Solar Energetic Particles
Tue-02 Aug | 08:00 – 10:00 | WB1
Distinguished Lecture – ST

Speaker(s): Yusuke EBIHARA, Kyoto University

Magnetosphere-Ionosphere Coupling and Consequent Disturbances: A Tribute to Dr. Yohsuke Kamide
Tue-02 Aug | 08:00 – 10:00 | WB1
Section Meeting – ST
Tue-02 Aug | 10:00 – 11:30 | MR18
AOGS Women’s Network Cell
Tue-02 Aug | 14:00 - 16:00 | WB2
SS01 - Solar Wind-Magnetosphere-Ionosphere Interaction, Magnetic Storms, and Substorms: Special Session in Memory of Prof. Yohsuke Kamide

Session Chair(s): Yoshiharu OMURA, Kyoto University, Jann-Yenq (Tiger) LIU, National Central University

SS01-A001 | Invited
Activities of Professor Yosuke Kamide in the Solar-terrestrial Environment Laboratory (STEL), Nagoya University

Nagoya University, Japan

Dr. Yosuke Kamide, a Nagoya University Professor Emeritus was a brilliant scientist in the physics of aurora and ionosphere-magnetosphere coupling processes. After he worked in US in 1973-1977 and in Kyoto-Sangyo University in 1977-1992, he moved to the Solar-Terrestrial Environmental Laboratory (STEL), Nagoya University, as a full professor for 1992-2007, including the term served as the director of STEL in 1999-2005. In STEL, he conducted state-of-art space weather research with a new facility called Geospace Environment Data Analysis System (GEDAS). He has also contributed to make the STEL, which was newly established in 1990, to an international institution, by inviting many top-class scientists to STEL and by organizing several important international conferences, such as the International Conference on Substorms-4 (ICS-4) at Lake Hamana on March 1998, the first STEP-Results, Applications, and Modeling Phase (S-RAMP) conference at Sapporo on October 2000, and the 23rd General Assembly of International Union of Geodesy and Geophysics (IUGG) in Sapporo on June-July 2003. His activities during the time of STEL also expanded to the international organizations. He was one of three major founders of Asia Oceania Geosciences Society (AOGS). He was a Vice President of the International Association of Geomagnetism and Aeronomy (IAGA) for 2003-2007 and member of several international committees of Committee on Space Research (COSPAR) and Scientific Committee on Solar-Terrestrial Physics (SCOSTEP). He acted as the editor of the Journal of Geophysical Research – Space Physics and Geophysical Research Letters for total eleven years. He was also enthusiastic for outreach of auroral sciences by publishing many public books and by editing a comic-book series of solar-terrestrial physics. The comic-book series are being further translated to more than ten languages in the world in collaboration with SCOSTEP. This translation activity is still going on, contributing widely to the public outreach of solar-terrestrial physics.

SS01-A002 | Invited
A Perspective on Yohsuke Kamide's Contributions to Solar-terrestrial Science

National Center for Atmospheric Research, United States

Yohsuke Kamide was a visionary scientist who opened up new avenues of research in solar-terrestrial physics. He had a profound influence on his numerous colleagues and students. It was my great pleasure to work with him for many years. One of Prof. Kamide's main scientific contributions was to develop a procedure for synthesizing polar magnetic perturbations into coherent time-varying patterns, from which the variations of ionospheric convection can be estimated. Analysis of these patterns enables individual observations to be interpreted in a global context, and reveals fundamental dynamic variations of the magnetosphere and their influence on the upper atmosphere. Prof. Kamide's service to the scientific community was also extraordinary, through his writings, editorships, meeting organization, and scientific outreach to the general public. His contributions are having a lasting impact.

SS01-A004 | Invited
Solar Wind-magnetosphere-ionosphere Interaction, Magnetic Storms, and Substorms: Special Session in Memory of Prof. Yohsuke Kamide

Michel BLANC#+
Research Institute in Astrophysics and Planetology, France

Prof. Kamide devoted most of his career to the study of external sources of magnetic variations and their relationships to current systems in space. He found unique ways to use the worldwide magnetometer network as a powerful diagnostics of these current systems and of the way they are driven by the interaction of the solar output with our planet’s environment. We owe him to a very large extent our modern view of these current systems and of the exchanges of momentum and energy they mediate. In this talk, I will briefly describe how our current understanding of these exchanges between the solar wind, magnetosphere and ionosphere changed thanks to Prof. Kamide’s work, how he described the role played by current systems in these exchanges, and how they can be traced by geomagnetic variations at a variety of spatial and temporal scales. I will particularly emphasize the emergence of a “system” representation of Earth’s geospace, in which different regions of entry (solar wind boundaries), transport, storage (magnetic tail lobes and ring current) and release (auroral zones, ring current decay) of energy from the solar wind are connected by plasma flows and energetic particle transport and coupled by current systems. His development of efficient and robust techniques for the monitoring of the dynamics of this system from ground-based magnetic variations is a central element in his legacy which illuminates the field of geomagnetic field and solar-terrestrial variations and will inspire for long the new generations of scientists.

SS01-A003 | Invited
Yohsuke Kamide and the Storm-substorm Controversy

Ioannis DAGLIS1,2#+
1University of Athens, Greece, 2Hellenic Space Center, Greece

It would not be an overstatement to say that Kamide sensei played a decisive and key role in the direction of my scientific career. In 1994 he asked me to deliver an invited talk on the role of oxygen ions in magnetic storm dynamics at the 21stAssembly of IUGG in Boulder, in July 1995. In the early stage of my research career I had focused on magnetospheric substorm dynamics and the invitation of Kamide sensei opened a new research chapter for me, which was very interesting and very productive. Obviously, I explored Kamide’s work on the topic of storm-substorm relationship and we had many discussions and collaborative efforts, although we did not agree. Despite our disagreements, Kamide sensei invited me to STELab for a three-month stay in 1998, which turned into something like an advanced school for me, as I had the opportunity for almost daily interaction with him. In my talk I refer to the basic points of Kamide’s work on the storm-substorm relationship and on some more recent developments that partly support Kamide’s view.

SS01-A005 | Invited
Toward the Understanding of Space Weather in the Polar Ionosphere

Beichen ZHANG#+
Polar Research Institute of China, China

This presentation, dedicated to Kamide sensei, introduces my memory of staying and working with sensei. I still recall the time when I expressed my idea to sensei to combine KRM magnetic inversion technique, which was well known and developed by sensei and his colleagues, and the polar ionospheric model to understand the global polar ionospheric physics during the meeting held in Beijing, 2001. Right after the Beijing meeting, I worked with Kamide sensei as COE postdoc in STELab, Nagoya University in the following two years. Studies will be recalled working together with Kamide sensei in the polar ionospheric physics, substorm dynamics etc. The last time I met with Kamide sensei was in 2016 AOGS meeting, Beijing. I will remember Kamide sensei’s excellent guidance and encouragement forever.

Tue-02 Aug | 16:00 - 19:00 | WB1
Education & Outreach - School Talks

Speaker(s): Steven D VANCE, California Institute of Technology, Cheng-Ling KUO, National Central University, Jann-Yenq (Tiger) LIU, National Central University

Wed-03 Aug | 12:00 – 14:00 | WB1
Kamide Lecture – AS

Speaker(s): Tsubasa KOHYAMA, Ochanomizu University

Synchronicity Discovered in the Gulf Stream and Kuroshio: A Path to Understanding Midlatitude Extreme Weather
Wed-03 Aug | 12:00 – 14:00 | WB1
Distinguished Lecture – AS

Speaker(s): Chung-Hsiung SUI, National Taiwan University

My Perspective of Convection Coupled Tropical Weather Disturbances and Intraseasonal Oscillations From Studies of Major Field Projects Over Tropical Oceans
Wed-03 Aug | 12:00 – 14:00 | WB1
Section Meeting – AS
Wed-03 Aug | 12:00 – 14:00 | WB2
Kamide Lecture – BG

Speaker(s): Anwesha GHOSH, Indian Institute of Science Education and Research Kolkata

Nitrogen Driven Niche Differentiation in Bacterioplankton Communities of Northeastern Coastal Bay of Bengal
Wed-03 Aug | 12:00 – 14:00 | WB2
Distinguished Lecture – BG

Speaker(s): Siew-Moi PHANG, University of Malaya & UCSI University

Use of Algae in Recycling of Nutrients Arising from Anthropogenic Activities
Wed-03 Aug | 12:00 – 14:00 | WB2
Section Meeting – BG
Wed-03 Aug | 16:00 – 17:00 | WB1
Wing Ip Medal Lecture

Speaker(s): Adam D. SWITZER, Nanyang Technological University

On the Need for Enhanced Interdisciplinary Research on the Historical and Geological Record of Past Coastal Hazard Events in the Asia Pacific Region
Wed-03 Aug | 18:00 - 20:00 | WB1
SS02 - Multidisciplinary Studies of the 2022 Tonga Volcanic Eruption and Associated Atmospheric/Ocean Waves

Session Chair(s): Kenji SATAKE, The University of Tokyo, Florian M. SCHWANDNER, NASA Ames Research Center

SS02-A006 | Invited
Extreme Explosivity of the 15 January 2022 Hunga Eruption, Tonga, Driven by Edifice Failure, Caldera Collapse and Magma-water Interaction

Shane CRONIN1#+, Taaniela KULA2, James WHITE3, Joali PAREDES MARINO1, Rachel BAXTER3, Ingrid UKSTINS1, Marco BRENNA3, Juanita RAUSCH4, David JARAMILLO-VOGEL4, David ADAMS1, Jie WU1, Geoff KILGOUR5, Simon BARKER6, Tobias DUERIG7
1The University of Auckland, New Zealand, 2Natural Resources Division. Ministry of Lands and Natural Resources, Tonga, 3University of Otago, New Zealand, 4Particle Vision GMBH, Switzerland, 5GNS Science, New Zealand, 6Victoria University of Wellington, New Zealand, 7University of Iceland, Iceland

Hunga Volcano in Tonga comprises a ~5 km-diameter caldera 140-150 m below sea-level. Historical Surtseyan eruptions occurred along caldera ring faults. The latest eruption began on 20 Dec 2021, near the 2014-15 vent. A >20 km high plume formed on 14 Jan 2022. On 15 Jan the climactic event was the largest explosion ever digitally recorded at peak eruption rate of ~109 kg/s. The event produced global air-pressure waves, tsunami and a >50 km-high eruption column. The whole pumice composition was similar to past events; 56 wt% SiO2 andesite. Mingled, crystal and microlite-poor glass spans 56-63 wt% SiO2 over micron-to mm scales. Up to ~10% volcanic/hydrothermal xenoliths occur. The fall deposit at 65-80 km is poorly sorted and fine-grained (4-7 wt% <1 mm). Juvenile clasts are dense (>2.7 g/cm3), with isolated vesicles. Minor <2-10% lower density (0.8-2.0 g/cm3) scoria lapilli (dmax 15 mm) fell out first. High-resolution SEM image counts show 70% of particles with hackle lines, stepped fractures, branched and conchoidal fractures. Dendrogrammatic statistical tests classify the curviplanar Tonga particles together with ash of the 2012 submarine Havre eruption. Properties of the juvenile tephra, along with the first observational insights from the vent area, show that the eruption was driven by shallow volcano-tectonic and hydrological processes. Available evidence suggests that edifice failure caused collapse and sudden caldera subsidence. Magma was rapidly squeezed from a hot and compositionally heterogeneous reservoir. Magma was fragmented very efficiently through sea-water infiltration into the edifice. The proportion of hackled/stepped fracture surfaces is higher than from recent major submarine eruptions. Subsequent post-eruption earthquakes suggest stepwise, piston-like subsidence of the magma reservoir, or magma re-injection.

SS02-A002 | Invited
Properties of the 2022 Hunga Tonga Volcano Eruption Aerosol Plume From Space-based Remote Sensing

Ralph KAHN1#+, Katherine JUNGHENN NOYES1, James LIMBACHER1,2, Verity FLOWER3
1NASA Goddard Space Flight Center, United States, 2Science Systems and Applications Inc, United States, 3University of Stirling, United Kingdom

Over the past few decades, satellite characterizing of volcanic eruption plumes has advanced, offering frequent global coverage of remote areas, and acquiring data safe from even the largest eruptions. Beginning with the 1991 Pinatubo eruption, aerosol plume extent, evolution, and even particle properties, were retrieved from space-based measurements. Due to its magnitude and resulting broad interest, the 2022 Hunga Tonga eruption in the South Pacific has been studied extensively by the satellite aerosol remote-sensing community. The volcano produced an explosive underwater eruption on 14 January 2022, propelling material well into the stratosphere. Within a few weeks, the plume traversed the entire southern hemisphere. Geostationary imagers captured the dramatic initial plume development, as the mass of ash, gas, and water vapor ascended far past the tropopause. Ultraviolet, visible, and infrared imagers in low-Earth-orbit tracked particles downwind to elevations > 40 km ASL, and provided some particle property information. Space-based lidar offered tighter altitude constraints on the spreading plume elements. These data were shared among the participants in the NASA Disaster Response Group and were then quickly distributed to early responders. A focus of this presentation will be results from the MISR instrument aboard NASA’s Terra satellite. MISR observed parts of the elevated plume as it traveled westward across the Pacific. As did other instruments, MISR retrieved an aerosol layer near the tropopause (~18 km elevation) and another at about 30 km. MISR retrieved non-spherical (presumably ash) particles on 15 January, but later, downwind results showed spherical, non-light-absorbing (likely sulfate/water) particles dominating. Other satellite and a few ground-based instruments obtained similar results. Preliminary MISR research-retrieval results indicate further that the effective particle size in the ~30 km layer increased downwind, possibly due to interactions with water injected during the initial eruption. This presentation will include updated results and conclusions.

SS02-A005 | Invited
Evacuation of a Complexly Zoned Reservoir During the 15th January 2022 Caldera Collapse Event at Hunga Volcano, Kingdom of Tonga

Marco BRENNA1#+, Ingrid UKSTINS2, Jie WU2, Shane CRONIN2, David ADAMS2, Alessio PONTESILLI3, Geoff KILGOUR4, Taaniela KULA5
1University of Otago, New Zealand, 2The University of Auckland, New Zealand, 3National Institute of Geophysics and Volcanology, Italy, 4GNS Science, New Zealand, 5Natural Resources Division. Ministry of Lands and Natural Resources, Tonga

The 15 January 2022 eruption of Hunga volcano in the Tongan Arc was the most violent of historical times. We have geochemically characterised juvenile material from the eruption. The bulk composition is SiO2 ~57.5 wt% and Mg# 42, similar to the reported liquid line of descent for Hunga magma, but more primitive than the 2014/15, 2009 and pre-AD1150 pyroclastic deposits (>59 wt% SiO2 and Mg#<37). Modal glass compositions are 56-58 wt% SiO2, with a wide range from 53 to 63 wt% SiO2 in part influenced by groundmass microlite crystallization but also reflecting chemically distinct melt batches. Minor populations of ~60-63 wt% SiO2 microlite free glass, as well as glass mingling textures are indicative of syn-eruptive assembly of heterogeneous melt populations at the time of eruption. Phenocryst phases of clinopyroxene, orthopyroxene and plagioclase are, on average, more primitive than previous eruptions, but compositional ranges are much broader and also include more evolved crystals than previously observed. Crystal cores are generally homogeneous with thin (<150 microns) rims that record normal, reverse, or oscillatory zonation, indicative of complex magma mixing processes. Equilibrium cpx-liquid pairs are used to derive eruptive temperatures of 1110-1130°C. Calculated pressures are within the previously estimated range for the Hunga reservoir at 5-7 km depth. The chemical data suggest rapid tapping and evacuation of a more primitive portions of the magma reservoir. Previous eruptions selectively extracted the evolved top of the reservoir, producing 2009 and 2014/15 events, as well as the larger pre-AD1150 events, but the 2022 eruption extracted more primitive material not previously observed. This event provides a snapshot of the Hunga magmatic system and captures a heterogeneous andesitic reservoir that was slowly being replenished by evolved basaltic andesite melt. Future activity of the volcano rests upon the replenishment rates for this reservoir.

SS02-A001 | Invited
What We Can See and What Can We Hear From Faraway?

Benoit TAISNE#+
Nanyang Technological University, Singapore

The eruption from the Hunga Tonga-Hunga Ha’apai volcano on 15th January 2022 sent a shock wave recorded all around the world, a large volcanic plume more than 20 kilometres (km) in the atmosphere, and a tsunami that affected many communities in Tonga and all around the world. There was also strong ashfall locally and reports of damage to infrastructure such as undersea cables vital to communications. The shock wave from the eruption was recorded by many infrasound stations and weather stations in the region. As Singapore is approximately 9,000 km away from the eruption, the signal from this shock wave took about eight hours to reach our sensors and was recorded at around 8:10pm local time the same day. Following the shock wave, the eruption signal lasted for about three hours on our sensors. Moreover, the shock wave travelled in all directions and was so strong that the sensors recorded a subsequent signal on 16 January at 3:31pm local time from the shock wave that travelled the opposite way around the globe. 

SS02-A007 | Invited
Fast-traveling Tsunamis by Atmospheric Pressure Disturbances on the 2022 Tonga Eruption

Tatsuhiko SAITO1#+, Tatsuya KUBOTA1, Kiwamu NISHIDA2
1National Research Institute for Earth Science and Disaster Resilience, Japan, 2The University of Tokyo, Japan

After the massive volcanic eruption of the 2022 Hung Tonga-Hunga Ha’api, tsunami-like waves were observed across the Pacific Ocean. The records showed some remarkable features that were not usually recognized in earthquake-generated tsunamis. One of the most notable characteristics was that the waves propagated considerably faster (~300m/s) than the velocity of tsunamis as free gravity waves (~200 m/s). As the strong atmospheric pressure disturbances generated by the eruption, called the Lamb wave, also propagated around the Earth’s surface with a velocity of ~300 m/s, the observed tsunami-like waves were considered to be excited by Lamb waves. We investigated the generation mechanism of the fast-traveling tsunamis with simulations using Lamb wave as tsunami source. The simulations confirmed that the fast-traveling tsunamis (~300m/s) were excited as forced oscillations by the external pressure disturbance. It should be noted that the forced oscillation does not cause a continuous increase of the wave height with the travel distance, unlike resonant coupling which occurs when the source propagates with the same velocity as tsunamis (e.g., Proudman 1929; Saito et al. 2021). Additionally, our numerical simulations found that the wave scattering of the forcibly-excited waves caused by islands and heterogenous bathymetry play a fundamental role in the generation of the tsunami energy. The scattering releases the free-propagating tsunamis from the forced oscillation. As a result, the tsunamis are more generated as scattering occurs. Our numerical simulation successfully reproduced the observed features of the tsunami waveforms arriving faster than the velocity of free-propagating tsunamis ~200m/s. However, the simulation tends to underestimate the height of late-arriving tsunamis. Slow-propagating atmospheric waves (~200 m/s) that were not included in our simulation might contribute to the generation of the late-arriving tsunamis.

SS02-A003 | Invited
Comprehensive Interdisciplinary Study on the 2022 Tonga Submarine Volcanic Eruption and Associated Tsunami: A Special Research Project Supported by MEXT, Japan

Anawat SUPPASRI1#+, Kenji SATAKE2, Takao OHMINATO2, Kiwamu NISHIDA2, Naoya SEKIYA2
1Tohoku University, Japan, 2The University of Tokyo, Japan

The tsunami caused by the Tonga submarine volcanic eruption that occurred at around 13:00 Japan Time (JST) on January 15, 2022, was a blind spot in Japan’s tsunami monitoring and warning system, which was established in 1952 for local tsunamis and expanded to distant tsunamis after the 1960 Chile tsunami. The sea waves arrived in Japan few hours earlier than expected by the current tsunami warning system of JMA. Tsunami warnings were issued in some areas in Japan and tsunami advisories were issued along the Pacific coast of Japan. There were no casualties in Japan, but the issues that emerged included difficulty evacuation and damage to fishery industries were reported and remained as future tasks. The Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) pointed out importance of this disaster and established a special research grant to support interdisciplinary researches related to this disaster and its impact. The research has 24 members from 18 universities and research institutes all over Japan which receive supports until March 2023. This invited talk will present the current progress, findings and remaining perspectives on four main research themes 1) Investigation of the volcanic eruption phenomenon, 2) Investigation of tsunami generation and propagation mechanism on a global scale due to volcanic atmospheric waves, 3) Investigation and survey of the impact of the Tonga eruptive tsunami on the coastal areas of Japan and 4) Social aspects survey on social impact in Japan causing by the tsunami.

Thu-04 Aug | 10:00 – 12:00 | WB1
Kamide Lecture – SE

Speaker(s): Jiashun HU, Southern University of Science and Technology

Data-Oriented Geodynamic Modeling and its Application to the Study of South American Tectonics Since the Late Cretaceous
Thu-04 Aug | 10:00 – 12:00 | WB1
Distinguished Lecture – SE

Speaker(s): Yih-Min WU, National Taiwan University & Academia Sinica

Development of Earthquake Warning and Shakemaps System Using Low-Cost Sensors in Taiwan
Thu-04 Aug | 10:00 – 12:00 | WB1
Section Meeting – SE
Thu-04 Aug | 12:00 – 14:00 | WB2
Kamide Lecture – OS

Speaker(s): Ayako YAMAMOTO, Tokyo University of Marine Science and Technology

Atlantic Multidecadal Sea Surface Temperature Variability in the Current and Changing Climate
Thu-04 Aug | 12:00 – 14:00 | WB2
Distinguished Lecture – OS

Speaker(s): Bo QIU, University of Hawaii at Manoa

Circulation and Climate Variability in the Extratropical North Pacific Ocean
Thu-04 Aug | 12:00 – 14:00 | WB2
Section Meeting – OS
Thu-04 Aug | 16:00 – 17:00 | WB1
Axford Medal Lecture

Speaker(s): Minhan DAI, Xiamen University

Ocean Carbon Cycle and Ocean-Based Carbon Dioxide Removal
Thu-04 Aug | 18:00 - 19:00 | WB2
Education & Outreach - School Talks

Speaker(s): Shengji WEI, Nanyang Technological University

What Do We Know and Don't Know about Volcanic Hazard? Insights from 2022 Hunga Tonga-hunga Ha'apai Volcano Eruption
Fri-05 Aug | 10:00 – 12:00 | WB1
Axford Lectures

Speaker(s): Daniel N. BAKER, University of Colorado Boulder, Janet SPRINTALL, Scripps Institute of Oceanography

Multi-Year Observations of the Earth’s High-Energy Radiation Environment

Daniel N. BAKER, University of Colorado Boulder

Detecting Change in the Climate System in the Indonesian Seas

Janet SPRINTALL, Scripps Institute of Oceanography

Fri-05 Aug | 16:00 – 17:30 | WB1
Closing, Awards & 2023 Annual Meeting


Tue-02 Aug | 08:00 - 09:30 | MR18

This year, we are trialling a novel Meet-the-Experts format to provide a space for experts and students to come together in a virtual way. To meet the challenge of our current circumstances each section will hold an online meet the experts group meeting. At the meeting both mentees and mentors will introduce themselves and describe their research interests in one of two sentences. Following introductions, one or two mentors will give an informal talk about their career paths, and the ups and downs they traversed along the way, particularly focussing on their early careers. Mentees will be encouraged to ask questions and seek advice about any aspect of academia they wish. Following this mentors and mentees may ask questions of any members participating in the meeting. We hope that this will result in lively discussions and interactions that may lead to future collaborations or prompt new research projects.

Wed-03 Aug | 12:00 - 13:30 | MR15

This year, we are trialling a novel Meet-the-Experts format to provide a space for experts and students to come together in a virtual way. To meet the challenge of our current circumstances each section will hold an online meet the experts group meeting. At the meeting both mentees and mentors will introduce themselves and describe their research interests in one of two sentences. Following introductions, one or two mentors will give an informal talk about their career paths, and the ups and downs they traversed along the way, particularly focussing on their early careers. Mentees will be encouraged to ask questions and seek advice about any aspect of academia they wish. Following this mentors and mentees may ask questions of any members participating in the meeting. We hope that this will result in lively discussions and interactions that may lead to future collaborations or prompt new research projects.

Thu-04 Aug | 10:00 – 11:30 | MR19

This year, we are trialling a novel Meet-the-Experts format to provide a space for experts and students to come together in a virtual way. To meet the challenge of our current circumstances each section will hold an online meet the experts group meeting. At the meeting both mentees and mentors will introduce themselves and describe their research interests in one of two sentences. Following introductions, one or two mentors will give an informal talk about their career paths, and the ups and downs they traversed along the way, particularly focussing on their early careers. Mentees will be encouraged to ask questions and seek advice about any aspect of academia they wish. Following this mentors and mentees may ask questions of any members participating in the meeting. We hope that this will result in lively discussions and interactions that may lead to future collaborations or prompt new research projects.

Fri-05 Aug | 14:00 - 15:30 | MR08

This year, we are trialling a novel Meet-the-Experts format to provide a space for experts and students to come together in a virtual way. To meet the challenge of our current circumstances each section will hold an online meet the experts group meeting. At the meeting both mentees and mentors will introduce themselves and describe their research interests in one of two sentences. Following introductions, one or two mentors will give an informal talk about their career paths, and the ups and downs they traversed along the way, particularly focussing on their early careers. Mentees will be encouraged to ask questions and seek advice about any aspect of academia they wish. Following this mentors and mentees may ask questions of any members participating in the meeting. We hope that this will result in lively discussions and interactions that may lead to future collaborations or prompt new research projects.

Atmospheric Sciences

Mon-01 Aug | 08:00 - 09:30 | MR01
AS02 - Climate Change and Tropical Climatic Hazards in Asia Oceania

Session Chair(s): Yuriy KULESHOV, Bureau of Meteorology

WMO Space-based Weather and Climate Extremes Monitoring (SWCEM) for East Asia and Western Pacific

Yuriy KULESHOV1,2#+, Toshiyuki KURINO3
1Bureau of Meteorology, Australia, 2Royal Melbourne Institute of Technology University, Australia, 3Japan Aerospace Exploration Agency, Japan

Recognizing needs to better utilize and improve monitoring of weather and climate extremes from space, the World Meteorological Organization (WMO) established a new flagship initiative - the Space-based Weather and Climate Extremes Monitoring (SWCEM). We started the SWCEM with the demonstration project for Asia-Pacific (2018-2019), and were able to bring clear benefits of translating science of satellite remote sensing to operational services at National Meteorological and Hydrological Services (NMHSs) in Member countries of WMO Regions II and V in a very short time. Recognizing SWCEM achievements in Asia and the Pacific, the Eighteenth World Meteorological Congress (Cg-18) in 2019 adopted the SWCEM Implementation Plan, endorsed its implementation from January 2020 in the region, and requested to consider the possibility of implementing similar projects in Africa and South America.
The demonstration project was focused on monitoring drought and heavy precipitation and it was implemented in geographical domain which covers the South-East Asia region and the Western Pacific Ocean area from 40°N to 45°S; 50°E to 120°W. The Japan Aerospace Exploration Agency (JAXA) and the Climate Prediction Center, National Oceanic and Atmospheric Administration (CPC/NOAA) provide satellite data and products for the region. SWCEM precipitation products produced by JAXA are based on the Global Satellite Mapping of Precipitation (GSMaP). CPC/NOAA provides SWCEM users with a similar set of products using the Climate Prediction Center morphing technique (CMORPH) satellite precipitation estimates. SWCEM space-based observations of precipitation have been incorporated into WMO activities strengthening capacity of Members, especially Small Island Developing States and Least Developed Countries, in climate change adaptation and disaster risk reduction. Satellite precipitation estimates and derived products are a significant contribution to strengthening Multi-Hazard Early Warning Systems. Currently, we are implementing it through the Climate Risk and Early Warning Systems (CREWS) projects.

AS02-A004 | Invited
New Version of the Global Satellite Mapping of Precipitation (GSMaP) Towards the Enhancement of WMO SWCEM Activities

Moeka YAMAJI1#+, Tomoko TASHIMA2, Munehisa K. YAMAMOTO1, Toshiyuki KURINO1, Takuji KUBOTA1
1Japan Aerospace Exploration Agency, Japan, 2Remote Sensing Technology Center of Japan, Japan

The World Meteorological Organization (WMO) has been initiated the Space-based Weather and Climate Extremes Monitoring (SWCEM) with the recognizing that there is a need to better utilize and improve the monitoring of weather and climate extremes from space. The Japan Aerospace Exploration Agency (JAXA) has participated in the project as one of meteorological or earth observation satellite operators. JAXA has been developed the Global Satellite Mapping of Precipitation (GSMaP) products with a resolution of 0.1 degrees, which is updated every hour, as part of the Global Precipitation Measurement (GPM) mission. In the SWCEM program, JAXA has provided the GSMaP Near-real-time Gauge-adjusted product with its 21-year climate normal since April 2000 to March 2021.In December 2021, the GSMaP algorithm was updated to version 8 by implementing various improvements to better estimate precipitation. In the new GSMaP retrieval algorithm using microwave radiometers, we expanded the retrieval latitude region to the poles from 60 degrees North and South. Some improvements were made in the retrieval method and newly input observation data of some sounder sensors. We also updated the database using precipitation radar in the retrieval algorithm, improve passive microwave and IR combined algorithm and gauge-adjustment method. Not only the estimation accuracy by updating the algorithm but also the data duration is important for the robustness of detecting extremes using GSMaP in the SWCEM activities. Therefore, JAXA is now reprocessing the GSMaP with the new algorithm (version 8) since January 1998. After the reprocessing, new version of the GSMaP data with 24-year climate normal will be utilized in the SWCEM program, leading to enhancement of the space-based weather and climate extremes detection.

Using WMO SWCEM Satellite Precipitation Estimates for Creating an Improved Satellite-gauge Dataset Over Australia

Zhi-Weng CHUA#+
Bureau of Meteorology, Australia

In our study, Australian station data along with the Japan Aerospace Exploration Agency’s (JAXA) Global Satellite Mapping of Precipitation (GSMaP) and the Bureau of Meteorology’s (BOM) Australian Gridded Climate Dataset (AGCD) rainfall analysis are combined to develop an improved satellite-gauge rainfall analysis over Australia that uses the strengths of the respective data sources. We investigated a variety of correction and blending methods with the aim of identifying the optimal blended dataset. The correction methods investigated were linear corrections to totals and anomalies, in addition to quantile-to-quantile matching. The blending methods tested used weights based on the error variance to MSWEP (Multi-Source Weighted Ensemble Product), distance to the closest gauge, and the error from a triple collocation analysis to ERA5 and Soil Moisture to Rain. A trade-off between away-from- and at-station performances was found, meaning there was a complementary nature between specific correction and blending methods. The most high-performance dataset was one corrected linearly to totals and subsequently blended to AGCD using an inverse error variance technique. This dataset demonstrated improved accuracy over its previous version, largely rectifying erroneous patches of excessive rainfall. Its modular use of individual datasets leads to potential applicability in other regions of the world. This dataset possessed strong performance at stations (similar to AGCD), in addition to improving upon AGCD in gauge-sparse regions.

Evaluating Satellite Soil Moisture Datasets for Drought Monitoring in Australia and the South-west Pacific

Jessica BHARDWAJ#+
Bureau of Meteorology, Australia

Soil moisture (SM) is a key agrometeorological indicator of drought intensity, severity and duration and is critical in monitoring the time-lagged impacts of drought. In Papua New Guinea and other Small Island Developing States (SIDS), there is a limited number, if any, in situ SM stations that can adequately assess soil-water availability in a near-real time context. Satellite SM datasets provide a viable alternative for SM monitoring and agrometeorological drought provision in these regions. In this study we investigate the performance of Soil Moisture Active Passive (SMAP), Soil Moisture and Ocean Salinity (SMOS), Soil Moisture Operational Products System (SMOPS) and SM from the Advanced Scatterometer (ASCAT) over Australia and key south-west Pacific SIDS. Australia is used as an initial SM testing ground given the presence of several in-situ SM monitoring stations and the Australian Bureau of Meteorology's state-of-art hydrological model – the Australian Water Resources Assessment (AWRA) landscape modelling system (AWRA-L). We further investigate SM satellite datasets in Australia and the south-west Pacific through Triple Collocation analysis that uses other SM reference datasets such as reanalysis SM data from the ERA-Interim mission and the Global Land Data Assimilation System (GLDAS) dataset produced by National Oceanic and Atmospheric Administration (NOAA). Results and study significance will be presented.

Climate Risk and Early Warning Systems (CREWS) International Initiative: Building Resilience of Papua New Guinea to Drought

Yuriy KULESHOV1,2#+
1Bureau of Meteorology, Australia, 2Royal Melbourne Institute of Technology University, Australia

Climate is rapidly changing on a global scale; significant changes in frequency and severity of many extreme weather and climate events have been observed since at least 1950. Developing and least developed countries are particularly vulnerable to the impact of climate extremes, including drought. Recognizing the urgency of enhancing early warning systems to assist vulnerable countries with climate change adaptation, the Climate Risk and Early Warning Systems (CREWS) international initiative has been established in 2015. In this presentation, CREWS activities in Papua New Guinea (PNG) are described. In PNG, severe drought caused by the strong El Niño in 2015-2016 affected about 40% of the population, with almost half a million people impacted by food shortages. The CREWS-PNG project aims to develop an improved drought monitoring and early warning system (EWS), running operationally through a collaboration between PNG National Weather Services and the Australian Bureau of Meteorology. The developed drought EWS will enable better strategic decision making for agriculture, water management, health and other climate-sensitive sectors. CREWS-PNG is implemented in partnership with the World Meteorological Organization (WMO) Space-based Weather and Climate Extremes Monitoring (SWCEM) initiative, to assist the PNG NWS with enhancing drought monitoring, observations network and weather forecasting. SWCEM project provides countries in WMO regions II and V, including PNG, with access to satellite precipitation estimates and derived products.

Validating a Tailored Disaster Risk Assessment Methodology: Drought Risk Assessment in Local PNG Regions

Bureau of Meteorology, Australia

Climate change is increasing the frequency and intensity of natural hazards, causing adverse impacts on vulnerable communities. Pacific Small Island Developing States (SIDS) are of particular concern, requiring resilient disaster risk management consisting of two key elements: proactivity and suitability. User-centred Integrated Early Warning Systems (I-EWSs) can inform resilient risk management. However, an EWS is only effectively integrated when all components are functioning adequately. In Pacific SIDS, the risk knowledge component of an I-EWS is underexplored. Risk knowledge is improved through efficient risk assessment. A case study assessing drought risk in PNG provinces was conducted to demonstrate the development and validate the application of an accurate and tailored risk assessment methodology. Hazard, vulnerability, and exposure indicators appropriate for monitoring drought in PNG provinces were selected. Risk indices for past years (2014-2020) were calculated and mapped in Geographic Information Systems (GIS). Risk assessment results were validated with a literature investigation of sources presenting information on previous droughts in PNG. The risk assessment indicated a strong drought event in 2015-2016, and a moderate event in 2019-2020. The literature corroborated this, confirming the validity of the risk assessment methodology. The methodology and results can be used to inform improved disaster risk management in PNG, by advising decision-makers of their risk and policymakers on which provinces are of priority for resource allocation. The methodology can also be used to enhance the risk knowledge component of a user-centred I-EWS and guide the implementation of such a system for drought in PNG and other Pacific SIDS.

Mon-01 Aug | 08:00 - 09:30 | MR07
AS18 - Carbon Neutrality, Clean Air and Regional Interactions

Session Chair(s): Jingxu WANG, Ocean University of China

AS18-A001 | Invited
Near-real-time Global Gridded Daily CO2 Emissions

Xinyu DOU#+, Zhu LIU
Tsinghua University, China

Precise and high-resolution carbon dioxide (CO2) emission data is of great importance of achieving the carbon neutrality around the world. Here we present for the first time the near-real-time Global Gridded Daily CO2 Emissions Dataset (called GRACED) from fossil fuel and cement production with a global spatial-resolution of 0.1° by 0.1° and a temporal-resolution of 1-day. Gridded fossil emissions are computed for different sectors based on the daily national CO2 emissions from near real time dataset (Carbon Monitor), the spatial patterns of point source emission dataset Global Carbon Grid (GID), Emission Database for Global Atmospheric Research (EDGAR) and spatiotemporal patters of satellite nitrogen dioxide (NO2) retrievals. Our study on the global CO2 emissions responds to the growing and urgent need for high-quality, fine-grained near-real-time CO2 emissions estimates to support global emissions monitoring across various spatial scales. We show the spatial patterns of emission changes for power, industry, residential consumption, ground transportation, domestic and international aviation, and international shipping sectors from January 1, 2019 to December 31, 2020. This gives thorough insights into the relative contributions from each sector. Furthermore, it provides the most up-to-date and finer-grained overview of where and when fossil CO2 emissions have decreased and rebounded in response to emergencies (e.g. COVID-19) and other disturbances of human activities than any previously published dataset. As the world recovers from the pandemic and decarbonizes its energy systems, regular updates of this dataset will enable policymakers to more closely monitor the effectiveness of climate and energy policies and quickly adapt.

Carbon Monitor Europe, A Near-real-time and Country-level Monitoring of EU27&UK CO2 Emissions

Piyu KE1#+, Zhu DENG1, Biqing ZHU1, Zhu LIU1, Philippe CIAIS2, Bo ZHENG1, Yilong WANG3, Olivier BOUCHER4, Feifan YAN5, Steven DAVIS6
1Tsinghua University, China, 2Le Laboratoire des Sciences du Climat et de l'Environnement, France, 3Institute of Geographic Sciences and Natural Resources Research, China, 4Institut Pierre-Simon Laplace, Sorbonne Université / National Centre for Scientific Research, France, 5Ocean University of China, China, 6University of California, Irvine, United States

With the growing ambition and urgency of climate change mitigation, many European Union countries raised time-bound national goals for carbon emissions reductions. However, annual estimates of national CO2 emissions can only provide historical changes and progress. Carbon Monitor has been producing near-real-time daily estimates of global CO2 emissions since 2020 which cover 7 main countries and regions of the world. Using a diverse range of activity data compiled from numerous sources, here we present near-real-time daily country-level and sector-specific emissions of 27 European Union countries and the United Kingdom from 2019 to 2021. Our results not only show the abrupt decreases in CO2 emissions due to lockdowns during the COVID-19 pandemic but the strong rebound in 2021. As EU countries recover from the pandemic, regular updates of this dataset will enable governments to monitor the effectiveness of climate and progress towards carbon neutrality.

Evaluating the Carbon Sink Capacity of Kunlun Mountain National Park Under Multiple Park Management Schemes

Qiuyu LIU1#+, Mingxi DU2, Li ZHAO2, Jiahuan GUO3, Xiang KANG2
1University of Quebec at Montreal, Canada, 2Xi'an Jiaotong University, China, 3Nanjing Forestry University, China

National Park, as an important part of the natural protected area, is the cornerstone for effectively maintaining biodiversity and mitigating global climate change. At present, China is in full swing to national parks as the main body of the natural protection system construction work, especially considering the urge target to achieve carbon neutrality and mitigate climate change for China. It is of great significance to accurately predict the carbon source and sink function and carbon storage of the national park ecosystem under global change for the national carbon neutralization strategy. Here based on the integration of advanced modeling, satellite measurements, and scenario analysis, this study will present our recent research about evaluating the carbon sink capacity of the proposed Kunlun Mountain National Park under a multiple management scheme. Our result will provide data and references for interdisciplinary scientists across fields of environmental management, ecology, and nature reserve sciences, as well as policymakers and the public.

Potential Health and Economic Impacts of Shifting Manufacturing From China to Indonesia or India

Qi RAN1+, Shao-Yi LEE2, Duofan ZHENG1, John MOORE3, Wenjie DONG1#
1Sun Yat-sen University, China, 2No Affiliation, Singapore, 3Beijing Normal University, China

The diversification or decoupling of production chains from China to alternative Asian countries such as India or Indonesia would impact the spatial distribution of anthropogenic emissions, with corresponding economic impacts due to mortality associated with particulate matter exposure. We evaluated these changes using the Community Earth System Model, the Integrated Exposure-Response (IER) model and Willingness To Pay (WTP) method. Significant effects on PM2.5 related mortality and economic cost for these deaths were seen in many East, Southeast and South Asian countries, particularly those immediately downwind of these three countries. Transferring all of export-related manufacturing to Indonesia resulted in significant mortality decreases in China and South Korea by 78k (5 per 100k) and 1k (2 per 100k) respectively, while Indonesia’s mortality significantly increased (73.7k; 29 per 100k), as well as India, Pakistan and Nepal. When production was transferred to India, mortality rates in East Asia show similar changes to the Indonesian scenario, while mortalities in India increased dramatically (87.9k; 6 per 100k), and mortalities in many neighbors of India were also severely increased. Nevertheless, the economic costs for these deaths were much smaller than national GDP changes in China (0.9% of GDP vs. 18.3% of GDP), India (2.7% of GDP vs. 84.3% of GDP) or Indonesia (9.4% of GDP vs. 337% of GDP) due to shifting all of export-related production lines from China to India or Indonesia. Morally, part of the benefits of economic activity should be used to compensate the neighboring communities where mortality increases occur.

Re-evaluating the Climate Impacts of Sulfur Emissions by Developed and Developing Countries From the Perspective of Consumption

Inner Mongolia University, China

International trade allows consumption of any region to be supplied by production worldwide. This affects the magnitude and geographical pattern of consumption associated emissions, which differ greatly from those of emissions associated with regional production (as in a typical emission inventory). Yet the climate influence of aerosols emissions associated with regional consumption remains unknown, despite that understanding this issue offers crucial information to support policymaking and international cooperation in climate change mitigation action from a consumption perspective. Here we quantify for the first time the effects of sulfate aerosol associated with consumption of developed and developing countries on global temperature and precipitation, by integrating a most current-generation fully coupled Earth system model (CESM2), a recent multi-regional input-output table (GTAP) and an updated emission inventory for CMIP6 climate simulations (CEDS). We find that despite large emission differences between developed and developing countries, consumption associated sulfur emissions of both regions lead to comparable impacts on the global mean surface air temperature. This is due to 1) the difference between developed and developing countries in the spatial distribution of consumption associated sulfate, and 2) the response of the nonlinear climate system to the spatial pattern of aerosol forcing. We further discuss the regional patterns of temperature and precipitation responses to sulfur emissions. This study serves as the first step of a comprehensive assessment of the climate response to the whole suite of consumption associated pollutants (black carbon, organic carbon, sulfate, ozone, etc.), complementing prevailing regional attribution analyses of climate change based on production associated emissions and radiation forcing.

Inequality in Historical Transboundary Anthropogenic PM2.5 and Ozone Health Impacts

Lulu CHEN#+, Jintai LIN, Ruijing NI
Peking University, China

Atmospheric transport of PM2.5 and ozone is estimated to exert substantial transboundary effects at present. During the past several decades, human-produced pollutant emissions have undergone drastic and regionally distinctive changes, yet it remains unclear about the resulting global transboundary health impacts. Here we show that between 1950 and 2014, global anthropogenic PM2.5 has led to 185.7 million premature deaths cumulatively, including about 14% from transboundary pollution. Among four country groups at different affluence levels, on a basis of per capita contribution to transboundary mortality, a richer region tends to exert severer cumulative health externality, with the poorest bearing the worst net externality after contrasting import and export of pollution mortality. The temporal changes in transboundary mortality and cross-regional inequality are substantial. We find that transboundary mortality increases by 27 times from 1951 to 2019, and on average contributes about 27% of global anthropogenic ozone-related deaths. All groups exert and suffer from substantial transboundary mortality. The high-income and upper middle groups have each experienced a reverse U-shaped relationship between its affluence and per-million-people contribution to transboundary mortality. The lower middle group has gradually matched the growth pathway of the upper middle group with a turning point less clear. Effort to reduce transboundary mortality should seek international collaborative strategies that account for historical responsibility and inequality.

Mon-01 Aug | 08:00 - 09:30 | MR08
AS14 - Machine Learning in Weather, Climate and Hydrological Analysis and Predictions

Session Chair(s): Rajib MAITY, Indian Institute of Technology Kharagpur, Venkata Ratnam JAYANTHI, Japan Agency for Marine-Earth Science and Technology

Using Machine Learning to Assess Uncertainty in Rainfall Climatology Products

Xinxin SUI#+
The University of Texas at Austin, United States

Characterizing error structures in precipitation products not only facilitates their proper applications for scientific and practical purposes but also helps improve their retrieval algorithms and processing methods. Despite the fact that multiple precipitation products have been assessed in the literature, factors that affect their error structures remain inadequately addressed. This study presents a novel approach to systematically and objectively analyze the error structure within precipitation products using decision trees. This data-driven method can analyze multiple factors simultaneously and disentangle the performance of precipitation products with various factors. By interpreting 60 binary decision trees, this study disentangles the error characteristics of precipitation products in terms of their spatiotemporal patterns and geographical characteristics. Two satellite-based and one reanalysis precipitation datasets, including the Integrated Multi-satellitE Retrievals for GPM (IMERG), Soil Moisture to Rain-Advanced SCATterometer (SM2RAIN-ASCAT), and the land component of the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5-Land), are evaluated for the contiguous United States (CONUS) from 2010 to 2019. The ground-based Stage IV precipitation dataset is used as the ground truth. Results indicate that IMERG and ERA5-Land perform better than SM2RAIN-ASCAT with higher accuracy and more stable interannual patterns for the analysis period. The conventional bias evaluation finds that ERA5-Land and SM2RAIN-ASCAT underestimate in summer and winter, respectively. The decision tree method cross-assesses three spatiotemporal factors and finds that underestimation of ERA5-Land occurs in the eastern part of the Rocky Mountains, and SM2RAIN-ASCAT underestimates precipitation over high latitudes, especially in winter. Additionally, the decision tree method ascribes system errors to nine geographical characteristics, of which the distance to the coast, soil type, and DEM are the three dominant features. On the other hand, the land cover type, topography position index, and aspect are three relatively weak factors.

Extracting 3D Radar Features to Improve Quantitative Precipitation Estimation in Complex Terrain Based on Deep Learning Neural Networks

Yung-Yun CHENG+, Chia-Tung CHANG, Buo-Fu CHEN#, Cheng-Shang LEE, Hung-Chi KUO
National Taiwan University, Taiwan

This paper proposes a new quantitative precipitation estimation (QPE) technique to provide accurate rainfall estimates in complex terrain, where conventional QPE has limitations. The operational radar QPE in Taiwan is mainly based on each Radar's single R(Z) relation and only utilizes the single-point lowest available echo to estimate rain rates, leading to low accuracy in complex terrain. Here, we conduct QPE using deep learning that extracts features from 3-D radar reflectivities to address the above issues. Convolutional neural networks (CNN) are used to analyze contoured frequency by altitude diagrams (CFADs) to generate the QPE. CNN models are trained on existing rain gauges in northern and eastern Taiwan with the three-year data during 2015−17 and validated and tested using 2018 data. To handle the unbalanced rainfall data and improve the accuracy, the weights of heavy rains (≧10 mm h-1) are increased in the model loss calculation. Results show that the CNN outperforms the R(Z) relation based on the 2018 rain-gauge data. Furthermore, this research proposes methods to conduct 2-D grided QPE to increase the forecast practicability. Verification based on independent rain gauges shows that the CNN QPE solves the underestimation of the R(Z) relation in mountainous areas. In addition, case studies are presented to visualize the results, showing that the CNN QPE generates better small-scale rainfall features and more accurate precipitation information. This deep learning QPE technique may be helpful for the disaster prevention of small-scale flash floods in complex terrain.

Prediction of Daily Air Temperature: Comparison of a Hybrid ML Approach With Four Other ML Approaches

Mohd Imran KHAN#+, Rajib MAITY
Indian Institute of Technology Kharagpur, India

In the present era of big data, artificial intelligence (AI) based machine learning (ML) is an important tool to trawl for the hidden associations between different hydrometeorological precursors and hydroclimatic variables. It is expected to reveal non-linear relationship, thereby, improving the weather forecast and future climate projections. Among several hydroclimatic variables, air temperature is one of the most contributing variables towards several climatic conditions severely impacting the flora and fauna species residing on earth at present and its impact is expected to intensify with time. The present study analyses the potential of a novel hybrid approach, namely Conv1D-LSTM, comprising of a one-dimensional Convolutional Neural Network (Conv1D) and Long Short Term Memory (LSTM) neural network in forecasting multi-step ahead (1-day to 10-day ahead) daily air temperature using hydrometeorological precursors. The proposed approach is applied to a few major highly urbanized areas in India, specifically 9 metropolitan cities, namely Ahmedabad, Bengaluru, Chennai, Hyderabad, Kolkata, Mumbai, New Delhi, Pune, and Surat. The performance is compared with four other popular ML approaches, viz. Conv1D, LSTM, Multi-Layer Perceptron (MLP), and Support Vector Regression (SVR). The aforesaid extensive evaluation is carried out using three statistical measures namely coefficient of correlation, root mean square error, and Nash-Sutcliffe efficiency, and shows a clear dominance of the hybrid approach at all lead times. The developed hybrid ML approach is expected to be useful in many fields of applications, even including electricity demand during different weather conditions and natural hazards such as wildfires, agriculture, design of solar power energy systems, etc.

Convolutional Neural Network-based Statistical Post-processing for Short-term Ensemble Precipitation Forecasts

Wentao LI+, Qingyun DUAN#
Hohai University, China

Raw forecasts from numerical weather prediction models suffer from systematic bias and cannot be directly used in applications such as hydrological forecasting. Statistical post-processing methods can be used to remove the bias and achieve reliable ensemble forecasts. However, traditional post-processing methods only use local precipitation forecasts as the only predictor, which limits their ability to extract information from raw forecasts. Therefore, we develop a LeNet-type convolutional neural network-based post-processing method for precipitation forecasts to fully make use of spatial information and auxiliary predictors and quantify uncertainty of forecasts. We compare the proposed model with a state-of-the-art post-processing model and an ANN-based model. The results show that CNN-based post-processing model performs better than traditional methods in forecast accuracy, especially for heavy rain. Moreover, CNN-based models transcend ANN-based model by using convolution layers to extract spatial information. Existing results illustrate the advantages of CNN-based post-processing models to extract spatial information and different meteorological auxiliary predictors to improve precipitation forecast skill.

Mon-01 Aug | 08:00 - 09:30 | MR04
AS06 - Mesoscale Meteorology and High-impact Weather

Session Chair(s): Chung-Chieh WANG, National Taiwan Normal University

A Comparative Study on Km-scale Simulations of the Extreme Rainfall Event Along the Northern Coast of Taiwan on 2 June 2017

Chung-Chieh WANG#+, Ting-Yu YEH
National Taiwan Normal University, Taiwan

In the present study, two experiments at 1-km grid size are compared on the extreme-rainfall event (up to 635 mm in 12 h) along the northern coast of Taiwan on 2 June 2017. The first is a forecast (F1km) that was driven by the best forecast member in a previous study at 3-km grid size (360 mm) and produced a peak amount of 541 mm along the northern shore (618 mm offshore), and the second is a simulation (S1km), driven by a 3-km simulation, that produced a maximum of 393 mm over land. The frontal moving speed are both slow in the two experiments, and the front spends slightly more time moving across the area in S1km (15 h) than in F1km (12 h). So, under similar conditions in most of the important factors previously identified, the present comparison allows us to examine the main differences between the peak rainfall amounts. The results show that in S1km, multiple rainbands moved slowly across northern Taiwan to produce the rainfall, with a more widespread heavy rainfall area, but the peak amount was less due to the transient nature of these rainbands (however slow they are). In F1km, on the contrary, linked to the presence of a low-pressure disturbance along the front, just to the north-northwest of Taiwan, the low-level westerlies were enhanced to produce a persistent convergence zone with the cold air behind the front, right across the northern tip of Taiwan without movement. Thus, one rainband remained at more or less the same location over several hours and produced the localized peak rainfall reaching 541 mm on land. The results indicate that it is possible to produce a higher peak amount with a finer grid size, but the predictability of such an extreme amount might be relatively low.

KDP Evolution and Heavy Rain Event in Northern Taiwan: Application of Polarimetric Radar on the Very-short-range Rainfall Forecast

Chi-June JUNG1+, Yucheng KAO2, Ben JOU1#
1National Taiwan University, Taiwan, 2Environmental Simulation Co. Ltd., Taiwan

On 16 October 2021, localized torrential rainfall (> 70 mm h-1) occurred in the slope area of northern Taiwan during an approaching surface front. Flash floods downstream of the catchment area resulted in a severe drowning accident without warning. In this observational study, the newly-established C-band disaster prevention rainfall radar in northern Taiwan is used for analysis and comparison. At local time 3-6 pm, extreme values of the specific differential phase KDP (> 2° km-1) can be used to identify the heavy rainfall region's location, intensity, and movement. For flash floods downstream of the catchment area, potentially, there is a priori warning capability. In this event, tracking intense and concentrated KDP on complex terrain has an advantage over radar reflectivity. The direct application of KDP on quantitative precipitation estimates can effectively complement the transmission-delay problem of ground rain gauges. This case also shows that intermittent lightning does not have much use for heavy rain warnings.

A New X-band Phased Array Weather Radar Network and Its Applications for High-impact Weather Observations and Warnings in Shanghai

Dai JIANHUA1,2#+
1Shanghai Central Meteorological Observatory, China, 2Shanghai Meteorological Service and Hunan Eastone Washon Technology Co., Ltd., China

Since Nov. 2018, the Shanghai Meteorological Service (SMS) of CMA and Hunan Eastone Washon Corporation have jointly designed and developed the Shanghai Urban Radar Demonstration Observation Project based on a new X-band Phased Array Weather Radar (PAWR) network.
The Shanghai PWAR network consists of five Eastone Washon X-band phased array radars. Each radar works as a transmitter and receiver (TR) or sub-array. The PWAR uses a flat panel antenna composed of multiple electronic units constituting a one-dimensional phased array, which can electronically scan in the elevation plane without moving the antenna. It achieves fast scanning by using a digital multi-beam technology and a fan-thin beaming method, by using 16 beams to scan 4 times simultaneously to complete the 0–90° elevation scan within 0.125s. The antenna rotates in azimuth to finish a volume scan within 30s, with a radial resolution of 30m and a max range of 45km.
The Shanghai PAWR network has shown advantages in detecting the structure and evolution of local severe storms, MCSs, tropical cyclone rainbands. Some cases related to severe convective storms are analyzed using the PAWR network in this paper. A mini-supercell with a tornado and its tornadogenesis within a mesoscale vortex embedded in a Meiyu front is discussed by using phased array radar, while the mini-supercell could not be identified by the Shanghai S-band radar. Comparisons with the operational S-band radars show that by using higher spatial and temporal resolution reflectivity and more accurate 3D wind retrieval data, the PWAR system can capture the structure and dynamics of precipitation systems or storms in better detail than any other radar systems. The high spatial and temporal information of the PWAR network provides an opportunity to increase lead time of nowcasting of extreme winds, heavy rain, and large hail in Shanghai.

Climatologies of Mesoscale Convective Systems Over China Observed by Spaceborne Radars

Hao CHEN+, Weixin XU#
Sun Yat-sen University, China

Mesoscale convective system (MCS) is the major contributor to seasonal rainfall and severe weathers in China. This study investigates the climatological characteristics of MCSs in China using 22-yr spaceborne precipitation radar observations, including MCS's spatial distribution, precipitation, environmental condition, convective intensity, and vertical structures. Compared to previous infrared-based studies, the TRMM-GPM MCS climatology shows far lower frequency over the Tibetan Plateau, greater topography-related gradients, and more realistic Meiyu rainband-associated signatures. Linear and non-linear MCSs account for 17% and 83% of the MCSs over China, respectively. Linear MCSs have much stronger convective intensity and heavier precipitation than non-linear MCSs, as indicated by TRMM convective proxies. Interestingly, though broad-stratiform MCSs own the weakest convection, they produce the heaviest (maximum) rainrate and the largest amount of heavy rainfall among non-linear MCSs. Among various types of linear MCSs, bow echoes (BEs) and no-stratiform (NS) systems exhibit the strongest convective intensity, embedded lines the weakest, and convective lines with trailing/leading stratiform in between. BEs and NSs share the most vertically extended structures, strongest microwave ice scattering, and highest lightning flashrates, but NSs have a much lower surface rainrate likely due to a drier environment. Vertical radar profiles suggest that both ice-based and warm-rain processes play an important role in the precipitation processes of linear MCSs over China, including the most intense BE storms. In short, this study helps to better understand the convective organizations, precipitation structures and ensemble microphysical properties of MCSs over China, and potentially provide guidelines for evaluating high-resolution model simulations and satellite rainfall retrievals on monsoonal MCSs.  

The Extreme Precipitation Research in the Southeastern Mountains of Yilan, Taiwan Under the Weak Synoptic Weather Condition

Hsun CHIU#+, Chung-Chieh WANG
National Taiwan Normal University, Taiwan

Due to the typhoon and its accompanied effect in the western North Pacific, observations have shown that the extreme precipitation areas frequently occur in the Yilan mountains of Taiwan, especially in the southeastern region. However, observations also showed heavy rainfall in this area as the tropical disturbances passed through the Bashi Channel and the northeast monsoon weakened. A long-lasting rainband can be found along the terrain by the radar observations, resulting in the prolonged extreme rainfall. Therefore, this is important for improving the forecast and the disaster prevention on the area under these above weather conditions.

Mon-01 Aug | 08:00 - 09:30 | MR05
AS17 - Regional Climate Downscaling and Cordex: Challenges and Prospects

Session Chair(s): Dong-Hyun CHA, Ulsan National Institute of Science and Technology

AS17-A017 | Invited
Dynamical Analyses for Future Changes of the Summer Precipitation in the Downscaled SSP Scenarios Over East Asia

Eun-Chul CHANG1#+, Tae-Min KIM1, Namgu YEO1, Joowan KIM1, Dong-Hyun CHA2, Ui-Yong BYUN1
1Kongju National University, Korea, South, 2Ulsan National Institute of Science and Technology, Korea, South

In this study, the downscaled regional climate change information from the Coordinated Regional Climate Downscaling Experiment (CORDEX) – East Asia (EA) is analyzed to find changes and causes of the summer precipitation over the EA monsoon region. The Global/Regional Integrated Model system (GRIMs) – Regional Model Program (RMP) is utilized for the dynamical downscaling of the global climate model results from the coupled model intercomparison project phase 6 (CMIP6) under the shared socioeconomic pathway (SSP) scenarios. It is shown that the downscaled future scenarios (SSP126 and SSP585) depict increased EA summer precipitation in comparison with the historical results. The major two forcing terms (i.e., the vorticity advection and the temperature advection) in the quasi-geostrophic omega equation are analyzed in order to explain causes of the precipitation increase. The increased thermal instability by temperature advection changes in the future period shows contributions to the enhanced upward motions which induce cloud-precipitation processes. The changes of the baroclinic instability are relatively not significant than the thermal instability changes. Presented results describe detailed processes how the global warming changes the future precipitation of the EA monsoon system by enhanced vertical circulation. 

Future Climate Change and its Uncertainty Assessment Using Bias-corrected High-resolution Multi-regional Climate Models Over East Asia

Changyong PARK+, Dong-Hyun CHA#, Seok-Woo SHIN
Ulsan National Institute of Science and Technology, Korea, South

The changes in uncertainty components for future temperature and precipitation projections on East Asia for bias-corrected high-resolution multi-RCMs were quantitatively evaluated. For temperature, the main uncertainty factors in the annual mean and all seasons during the near-term projection are internal variability and model uncertainty, which decrease as time increases. The scenario uncertainty will tend to increase continuously. These results by RCMs are consistent with those of previous studies performed using GCMs. In the case of precipitation, the main uncertainty factors for the annual average and all seasons for the near-term projection are internal variability and model uncertainty. However, the main difference from temperature is that precipitation is predicted to have a significant contribution of internal variability even in the long-term projection from the fraction of total variance. In the results of annual precipitation and summer precipitation, model uncertainty due to differences in dynamical mechanisms between RCMs was found to be a major factor in precipitation uncertainty. Therefore, if the performance of the models is advanced through the improvement of the dynamical mechanism, the model uncertainty will be reduced, which will eventually narrow the total uncertainty. In winter precipitation, the scenario uncertainty due to the strengthening of climate change signals in long-term projection is expected to be the most dominant uncertainty component. In both temperature and precipitation of the near-term projection, the internal variability in the magnitude of fractional uncertainty and the fraction of total variance was predicted to be larger in South Korea than in East Asia. The importance of internal variability at a smaller regional scale during the near-term projection was confirmed not only in the GCMs in the previous studies but also in the RCMs of this study.

Future Projection of the Impact of Heat Waves on the Electricity Demand in South Korea

Yujin KIM1#+, Youngeun CHOI2, Seung-Ki MIN1
1Pohang University of Science and Technology, Korea, South, 2Konkuk University, Korea, South

This study examined changes in the characteristics of heat waves (HWs) in South Korea by considering the spatial extent, intensity, and duration of the HWs, and projected future changes in electricity demands by identifying the relationship between HW characteristics and electricity demands. The magnitude is a new index that more accurately evaluates the effect of extreme high temperatures, and is calculated as the average intensity of the heat wave day (HWD) weighted with spatial extent. The frequency and magnitude of HWs have significantly increased during 1973-2019. According to the Representative Concentration Pathways (RCP) 8.5 scenario simulations, it was projected that wide, strong, and long-lasting HWs that have not been experienced would occur frequently in the late 21st century (2071-2100). Observations showed that the larger spatial extent, stronger intensity, and longer duration of HWs are associated with the higher demand for electricity. Based on the observed relationship, we provided an improved multiple regression model for electricity demand prediction, which includes the magnitude and duration of HWs as explanatory factors. According to the proposed model, in the late 21st century, the daily peak electricity demands on HWDs were projected to increase by 9.1% compared to the present. In particular, the extreme value of daily peak electricity demand (30-yrs return level) was projected to increase by 19.1%, which was found to be alleviated to 4.6% when greenhouse gas emission is reduced following the RCP 2.6 scenario. 

Evaluation of East Asian Winter Monsoon Simulated by Multi-regional Climate Models and Their Systematic Errors

Seok-Woo SHIN1+, Changyong PARK1, Minkyu LEE2, Taehyung KIM1, Dong-Hyun CHA1#
1Ulsan National Institute of Science and Technology, Korea, South, 2Pohang University of Science and Technology, Korea, South

East Asian Winter Monsoon (EAWM) is an important system, which has a significant impact on extreme winter phenomena, in East Asia including the Korean Peninsula. EAWM is characterized by Siberian high with cold air and Aleutian low with warm air, north wind in the lower troposphere, East Asian trough in the middle troposphere, and East Asian jet stream in the upper troposphere. According to several previous studies, the variability of EAWM, which can be affected by human activity and climate change, is strongly correlated with the occurrence of cold waves in East Asia and is one of the precipitation mechanisms for winter on the Korean Peninsula. Extreme winter phenomena such as cold waves and heavy snow related to EAWM are closely related to life and socio-economic damage. Meanwhile, the regional climate model (RCM) with an added value in regional simulation for extreme climate phenomena has internal variability, which can increase uncertainty in future climate projection. Therefore, in this study, in order to closely understand EAWM and lower the uncertainty of future climate projection, the simulation performance of multi-RCMs (SNURCM, HadGEM3-RA, WRF, and CCLM) was evaluated through spatiotemporal analysis. Specifically, precipitation, temperature, and atmospheric fields related to EAWM were analyzed using observation (APHRODITE, GPCP, etc.), reanalysis (ERA-Interim, ERA5, etc.), and multi-RCMs data. The results showed that multi-RCMs could capture the spatial distribution of EAWM despite the intensity difference of EAWM. We confirmed that the systematic errors of temperature and precipitation related to EAWM in multi-RCMs were influenced by temperature advection, sea surface temperature, and lower wind. Afterward, we are going to analyze the mechanism of the systematic errors quantitatively and closely.

The Australian Climate Service (ACS) Strategy for Regional Modelling and Climate Projections

Chloe MACKALLAH1#+, Michael GROSE1, Sugata NARSEY2, Andrew DOWDY2, Chun-Hsu SU2, Marcus THATCHER1, Francois DELAGE2, Ulrike BENDE-MICHL2, Benjamin NG1, Alicia TAKBASH1
1Commonwealth Scientific and Industrial Research Organisation, Australia, 2Bureau of Meteorology, Australia

The newly formed Australian Climate Service (ACS) aims to become an authoritative source of climate and hazard information that enhances our ability to prepare for, respond to, and recover from the impacts of natural hazards in a changing climate. Here we outline the modelling strategy for the production of climate projections data and information that will underpin the ACS. The ACS program will draw on the breadth of data available from the sixth phase of the Coupled Model Inter-comparison Project (CMIP6), including a direct analysis of several CMIP6-based large ensembles such as the 40-member ensemble produced by ACCESS-ESM1.5, a multi-model regional climate modelling ensemble produced under CORDEX2 protocols, and targeted convective-scale simulations for selected regions. The CORDEX2 ensemble will follow a ‘sparse matrix’ approach, including simulations from CCAM and BARPA which have been commissioned for the program, and will leverage work done for NARCliM, the Queensland state projections work, and international contributions to CORDEX Australasia. Host GCM selection from the CMIP6 archive has been guided by several factors, including data limitations, model performance, model independence, and representativeness in the projected change signal. Selection also accounts for the uneven spread of equilibrium climate sensitivities in CMIP6, noting the new ‘likely’ range defined in the IPCC Sixth Assessment Report. There are various challenges and considerations when using climate model data to derive quantitative and reliable projections, and here we outline the proposed model evaluation, model sub-selection and weighting, bias correction, and verification methods that will be deployed to produce these projections.

Considering Model Independence in Regional Climate Model Selection

Jason EVANS1#+, Chris THOMAS1, Giovanni DI VIRGILIO2, Fei JI2, Eugene TAM2
1University of New South Wales, Australia, 2NSW Department of Planning and Environment, Australia

Climate models are not independent representations of the climate system, often sharing methods and code. This lack of independence means that climate model ensembles are not well represented as statistically independent samples. Hence, existing large climate model ensembles have been estimated to contain the same amount of information as would be contained in a much smaller set of independent models. Dynamical downscaling is usually constrained by computational resources such that only a subset of available models can be used. By choosing the most independent models in the ensemble the maximum amount of information can be retained for downscaling. Several methods to account for this model dependence have been proposed in recent years. These methods use very different approaches to defining and measuring model dependence. Here we apply three different techniques to an ensemble of 78 regional climate model simulations and assess the implications for independence-based model subset selection. While models indicated as most independent can differ between methods, a high level of agreement is found for the 10% most independent models.

Mon-01 Aug | 08:00 - 09:30 | MR06
AS01 - Passive and Active Sensing of the Chemistry and Dynamics of the Middle and Upper Atmosphere

Session Chair(s): Iain REID, ATRAD Pty. Ltd.

C-Structures Observed in Mesospheric Sodium and Potassium Layers

Vania ANDRIOLI1,2#+, Jiyao XU3, Paulo BATISTA2, Alexandre PIMENTA2, Maria MARTINS2, Laysa RESENDE4, Siomel SAVIO2, Cristiane TARGON2, Guotao YANG1, Jing JIAO1, Chi WANG1, Zhengkuan LIU1
1Chinese Academy of Sciences, China, 2National Institute for Space Research, Brazil, 3State Key Laboratory of Space Weather, China, 4China-Brazil State Key Laboratory for Space Weather, Brazil

In the present work, we analyzed the C-Structures Sporadic layers in the mesospheric metal layers using a high-resolution simultaneous Sodium and Potassium LIDAR, operating at São José dos Campos, Brazil (23°S,46°W). These events have different characteristics from those thin layers of metal concentration enhancement as reported for the first time by Clemesha et al. (1978). The present study focuses on these much rarer events that appear as C-shaped structures in the lidar height/time display. A total of 9 C-Structures events were found within 185 nights of simultaneous Na-K LIDAR data, measured between 2017 and 2019. These events show an averaging height range of 5.1 km. They last from half to a few hours, 90 min on average. We also used ionosonde for Es layer investigation and wind measurements from an all-sky interferometric meteor wind radar, both located at Cachoeira Paulista, a nearby location. An analysis of their formation, together with simultaneous meteor winds and Es measurements, as well their similar characteristics in both Na and K layers, suggests that the observed structures might be the result of the wind-shear distortion of pre-existing clouds of enhanced sodium and potassium concentration.

Observations of the Richardson Number by the MIGHTI on the NASA ICON Satellite, and Dynamic Instability Near the Turbopause

Gary SWENSON1#+, Scott ENGLAND2, Jeffrey FORBES3
1University of Illinois at Urbana-Champaign, United States, 2Virginia Tech, United States, 3University of Colorado Boulder, United States

The Richardson number (Ri), which combines the convective state of the atmosphere with wind shear, describes a criterion which leads to Kelvin-Helmholtz instabilities (KHI) and turbulence when Ri<0.25.  Observations in the MLT using lidars, ground-based imagers, and chemical releases have provided insights to conditions that leads to KHI. The NASA ICON satellite instrumented with the MIGHTI (Michelson Interferometer for Global High-resolution Thermosphere Imaging) instruments provide Doppler winds and separately, molecular rotational temperatures from the O2 Atmospheric band emissions. These observations were used to determine the Ri between 98 and 106 km, a region where turbulence generated eddy diffusion competes with molecular diffusion, defining the altitude of the turbopause (~100km) and the vertical flux of minor constituents and heat. The analysis reported herein is for 2020, where the intra-annual, diurnal, and latitudinal (four zones between 12oS and 36oN) values are determined.  The conclusion from these measurements is that the region is near, or in KHI conditions most of the time, with no discernable change with the day of the year, but a slightly higher probability of unstable conditions in the equatorial region than at midlatitude.  It has been understood that this region is characteristically dominated by large amplitude tides (and shears), but the extent and consistency in time and space strongly supports the importance they have in the generation of KHI near the turbopause.

Observing Mesospheric Neutral Wind With Electrojet Zeeman Imaging Explorer (EZIE)

Astrid MAUTE1#+, Rafael ARAUJO DE MESQUITA2, Heikki VANHAMAKI3, Patrick ESPY4,5, Karl LAUNDAL5, Jeng-Hwa YEE2, Jesper GJERLOEV2, Wenbin WANG1
1National Center for Atmospheric Research, United States, 2The Johns Hopkins University Applied Physics Laboratory, United States, 3University of Oulu, Finland, 4Norwegian University of Science and Technology, Norway, 5University of Bergen, Norway

The Electrojet Zeeman Imaging Explorer (EZIE) is a NASA CubeSat mission focused on studying the auroral electrojet current system in Earth’s atmosphere by measuring for the first time the magnetic signal in the 80 km altitude range. EZIE consists of three CubeSats, each equipped with four beams looking downward toward nadir direction, able to measure the molecular oxygen thermal emission and derive the magnetic field via Zeeman splitting. In addition to the magnetic field, highly precise line-of-sight neutral wind and temperature measurements can be retrieved by observing the O2 emission. This presentation will give an overview of the EZIE mission and details about the anticipated wind retrieval with respect to expected precision, flexible observing geometry, and location.  To gain further insights into the ability to capture the local wind system we use high-resolution Whole Atmosphere Community Climate Model eXtended (WACCM-X) simulations to develop Observing System Simulation Experiments (OSSE). We will show examples of the OSSE used in the wind fitting based on the Spherical elementary current system (SECS) method to demonstrate the capabilities of the EZIE mission. EZIE is scheduled to launch in the fall of 2024.

AS01-A008 | Invited
The Ground–based Airglow Network in China and Research Progresses

Jiyao XU#+
Chinese Academy of Sciences, China

Recent observational studies have found that the topographic environment has an important impact on the middle and upper atmosphere and ionosphere, and the fluctuation characteristics of the middle and upper atmosphere and ionosphere are different in different latitudes and longitudes. China, from north to south, spans from the middle latitudes to the low latitude both in geographic latitude and geomagnetic latitude. And China has a variety of topography environment, which including high lands, hill, plains, seas, and long coasts. This is a natural laboratory to study the effects of different latitudes and topography on the middle and upper atmosphere. Airglow observation is one of the important means to study the middle and upper atmosphere. We have established a ground-based airglow network in China gradually since 2010, which consists of 16 stations and more than 40 all sky imagers. The network almost covers China and has double-layer detection capability, which focuses on two airglow layers: the red line of atomic oxygen (~250 km) and OH (~87 km) airglow layers. In some stations, we also make observations of green line and 777.4 nm of atomic oxygen and sodium layer airglow at 589 nm.  This report will introduce the airglow network and related research progresses, which include thunderstorm and typhoon effects, influence of Tibet Plateau on gravity waves, characteristic of equatorial plasma bubble (EPB) and medium-scale traveling ionospheric disturbance (MSTIDs), and so on.

Long-term Meteor Wind Observations as By-products of Routine Mesosphere Measurements of PANSY Radar, Antarctica

Masaki TSUTSUMI1#+, Taishi HASHIMOTO1, Koji NISHIMURA2, Toru SATO2, Masashi KOHMA3, Kaoru SATO3
1National Institute of Polar Research, Japan, 2Kyoto University, Japan, 3The University of Tokyo, Japan

PANSY radar at Syowa station (69S, 39E) has been conducting continuous mesosphere, stratosphere and troposphere observations as the only MST/IS radar in the Antarctic [Sato et al., 2014, JASTP]. These observation techniques are characterized by their three dimensional wind velocity measurement ability including vertical wind component with high time/height resolutions. The mesosphere observations, however, need ionized media in the mesosphere and are limited to day-light hours. To compensate this we have developed an external interferometry system for reception which can detect meteor echoes throughout a day in the height region of 70-95 km as purely by-products of the routine mesosphere measurements. A pioneering external meteor system attached to the MU radar, Japan, by Nakamura et al [1997, Radio Sci.] is a proto-type of the current system. The newly developed system, consisting of five Yagi antennas, has continuously been operating since March 2021. The number of detected meteor echoes is comparable to or even more than that of commercial meteor radars. Inter-comparison with the routine mesosphere wind measurements and analyses of mean winds and atmospheric waves are to be made.

Mon-01 Aug | 08:00 - 09:30 | MR03
AS05 - El Niño Complexity and Change

Session Chair(s): Malte STUECKER, University of Hawaii at Manoa

AS05-A001 | Invited
Pleistocene El Niño Complexity

Axel TIMMERMANN#+, Sun-Seon LEE, Kyung-Sook YUN
Pusan National University, Korea, South

How ENSO has changed during the Pleistocene has remained elusive. Here we present results from the first transient simulation conducted to date with a Coupled General Circulation Model (CESM1.2) which covers earth's history of the past 3 million years. The model simulation uses acceleration of the external forcings by a factor of 5. Therefore, the entire CESM1.2 dataset available comprises 600,000 model years. Our analysis focuses on the combined effects of CO2, orbital and ice-sheet forcing on tropical mean climate, the annual cycle and ENSO dynamics. We will discuss the effect of the mid-Pleistocene transition on ENSO complexity and the forcing combinations that generate the most extreme El Niño events during the entire Pleistocene. We will compare the projected future ENSO changes in CESM1.2 with those from the paleo-simulation to determine the potential emergence of no-analogue conditions.

AS05-A002 | Invited
Increased ENSO Sea Surface Temperature Variability Under Four IPCC Emission Scenarios

Wenju CAI1,2#+, Benjamin NG2
1Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, China, 2Commonwealth Scientific and Industrial Research Organisation, Australia

Sea surface temperature (SST) variability of El Niño-Southern Oscillation (ENSO) underpins its global impact, and its future change is a long-standing science issue. In its sixth assessment, the Intergovernmental Panel on Climate Change (IPCC) reaffirms increased ENSO extreme rainfall anomalies but reports no systematic change in ENSO SST variability under any emission scenarios considered.  However, comparison between the 20th and 21st century shows a robust increase in century-long ENSO SST variability under four IPCC plausible emission scenarios.

AS05-A007 | Invited
Extreme El Niño Events in a Changing Climate

Samantha STEVENSON#+
University of California Santa Barbara, United States

The majority of future projections in the Coupled Model Intercomparison Project (CMIP5) show more frequent exceedances of the 5 mm day21 rainfall threshold in the eastern equatorial Pacific rainfall during El Niño, pre- viously described in the literature as an increase in ‘‘extreme El Niño events’’; however, these exceedance frequencies vary widely across models, and in some projections actually decrease. Here we combine single-model large ensemble simulations with phase 5 of the Coupled Model Intercomparison Project (CMIP5) to diagnose the mechanisms for these differences. The sensitivity of precipitation to local SST anomalies increases consistently across CMIP-class models, tending to amplify extreme El Niño occurrence; however, changes to the magnitude of ENSO-related SST variability can drastically influence the results, indicating that understanding changes to SST variability remains imperative. Future El Niño rainfall intensifies most in models with 1) larger historical cold SST biases in the central equatorial Pacific, which inhibit future increases in local convective cloud shading, enabling more local warming; and 2) smaller historical warm SST biases in the far eastern equatorial Pacific, which enhance future reductions in stratus cloud, enabling more local warming. These competing mechanisms complicate efforts to determine whether CMIP5 models under- or overestimate the future impacts of climate change on El Niño rainfall and its global impacts. However, the relation between future projections and historical biases suggests the possibility of using observable metrics as ‘‘emergent constraints’’ on future extreme El Niño, and a proof of concept using SSTA variance, precipitation sensitivity to SST, and regional SST trends is presented.

Mechanisms for Multi-year ENSO Using Reanalysis and CMIP6 Models

Tomoki IWAKIRI#+, Masahiro WATANABE
The University of Tokyo, Japan

El Niño-Southern Oscillation (ENSO) events occasionally recur one after the other in the same polarity, called multi-year ENSO. To date, multi-year El Niño and La Niña have been investigated separately in the literature. Given the lack of comprehensive understanding to this phenomenon, this study aims at clarifying mechanisms of multi-year El Niño and La Niña in a unified manner. Mechanisms for multi-year ENSO are explored using atmosphere and ocean reanalysis datasets. It is first confirmed that multi-year El Niño and La Niña events account for approximately 30% and 60% of the respective total events. Because multi-year El Niño and La Niña events are, with a few exceptions, roughly symmetric in its characteristics (i.e., duration and magnitude), they are combined to produce a composite time evolution of multi-year ENSO, which is compared with conventional single-year ENSO. For the multi-year ENSO event, anomalous upper-ocean heat content (OHC) in the equatorial Pacific does not change the sign during the first peak, which stimulates another event to occur in the following year. The ocean heat budget analysis showed that this prolonged OHC anomaly is caused by meridional surface Ekman heat transports counteracting geostrophic transports that otherwise act to change the OHC anomaly. A latitudinally wide pattern of sea surface temperature (SST) anomaly observed during the multi-year events is responsible for the net Ekman transport to recharge/discharge the equatorial ocean mass during the first decay phase of multi-year El Niño/La Niña. Climate simulations by Coupled Model Intercomparison Project Phase 6 (CMIP6) Earth System models support the above mechanism and show a significant correlation between the meridional width of the ENSO SST anomalies and the occurrence ratio of multi-year ENSO events across the models.

Relations Between Interannual Variability of Regional-scale Indonesian Precipitation and Large-scale Climate Modes During 1960-2007

Givo ALSEPAN#+, Shoshiro MINOBE
Hokkaido University, Japan

Regional-scale precipitation responses over Indonesia to major climate modes in the tropical Indo–Pacific Oceans, i.e., canonical El Niño, El Niño Modoki, and the Indian Ocean Dipole (IOD), and how the responses are related to large-scale moisture convergences are investigated. The precipitation responses, analyzed using a high-spatial-resolution terrestrial precipitation dataset for the period 1960–2007, exhibit differences between the dry (July–September) and wet (November–April) seasons. Canonical El Niño strongly reduces precipitation in central to eastern Indonesia from the dry season to the early wet season and northern Indonesia in the wet season. El Niño Modoki also reduces precipitation in central to eastern Indonesia during the dry season, but conversely increases precipitation in western Indonesia during the wet season. Moisture flux analysis indicates that corresponding to the dry (wet) season precipitation reduction due to the canonical El Niño and El Niño Modoki anomalous divergence occurs around the southern (northern) edge of the convergence zone when one of the two edges is located near the equator (10°S–15°N) associated with their seasonal migration. This largely explains the seasonality and regionality of precipitation responses to canonical El Niño and El Niño Modoki. IOD reduces precipitation in southwestern Indonesia in the dry season, associated with anomalous moisture flux divergence. The seasonality of precipitation response to IOD is likely to be controlled by the seasonality of local sea surface temperature anomalies in the eastern pole of the IOD.

Mon-01 Aug | 08:00 - 09:30 | MR02
AS03 - The Asian Monsoon: Past, Present and the Future

Session Chair(s): Ramesh KRIPALANI, Indian Institute of Tropical Meteorology, Renguang WU, Zhejiang University, Kyung-Ja HA, Pusan National University

Changing Influence of ENSO on Indochina Peninsula Rainfall

Renguang WU1#+, Yiya YANG2, Yu SHI1, Peijun ZHU1
1Zhejiang University, China, 2Bejing Meteorological Service, China

El Niño-Southern Oscillation (ENSO) plays an important role in rainfall variability over various regions in Asia, including the Indochina Peninsula (ICP). The influence of ENSO on regional rainfall variability may vary with the season and display interdecadal changes. This talk presents evidence for different impacts of ENSO on the ICP rainfall variability in different stages of the rainy season and interdecadal changes in the relationship of ICP rainfall to ENSO. More May-June, July-August and October-November rainfall falls over the ICP in the La Niña decaying years, La Niña decaying years and/or El Niño developing years, and La Niña developing years, respectively, during 1979-2016. The formation of rainfall anomalies in the three stages is attributed to a combined effect of regional SST anomalies in different regions. The relationship of May ICP precipitation to ENSO experienced interdecadal changes during 1951-2016. During the 1950s through the late-1970s, more (less) ICP rainfall tends to occur in May of La Niña (El Niño) developing years, whereas after the late-1990s, more (less) ICP rainfall tends to appear in May of La Niña (El Niño) decaying years. During the late-1970s through the late-1990s, more (less) ICP rainfall occurs in May of La Niña (El Niño) persisting years. The interdecadal change in the ICP May rainfall-ENSO relationship is related to changes in the developing time of ENSO events and tropical Indo-Pacific SST anomaly pattern. A prominent change is detected in the relationship between August ICP rainfall and tropical Pacific SST around 1980. More August ICP rainfall falls in La Niña developing years during 1959-1979, but in El Niño developing years during 1983-2003. The change is associated with a different temporal evolution of equatorial Pacific SST anomalies before and after 1980.

Different Asian Rainfall Anomaly Patterns Associated with Early and Peak Summer Rainfall Variation Over the Indochina Peninsula

Yu SHI#+, Renguang WU
Zhejiang University, China

This study investigates the rainfall anomaly patterns over Asia associated with interannual variations of early summer (May-June) and peak summer (July-August) Indochina Peninsula (ICP) rainfall during 1979-2016. The early and peak summer rainfall variation in the ICP displays an out-of-phase relation to that in central Asia and central China, respectively. The out-of-phase early summer rainfall variation between the ICP and central Asia tends to occur in ENSO decaying years and the out-of-phase peak summer rainfall variation between the ICP and central China tends to occur in ENSO developing years. The early summer out-of-phase rainfall anomaly pattern between the ICP and central Asia forms due to a Rossby wave type response to anomalous heating extending from the ICP to northeast India, which is attributed to a combined influence of same sign SST anomalies in the equatorial central-eastern Pacific and southwestern tropical Indian Ocean and opposite sign SST anomalies in the tropical western North Pacific. The peak summer out-of-phase rainfall variation between the ICP and central China forms due to a meridional atmospheric circulation pattern over East Asia and the western North Pacific, which is resulted from the combined impacts of opposite SST anomalies in the equatorial central-eastern Pacific and tropical southeastern Indian Ocean.

Contribution of Precipitation and Temperature to Drought Variations Over Asia

Jianmin ZHANG#+, Renguang WU
Zhejiang University, China

Droughts are among the most damaging natural disasters over Asia. The occurrence of droughts is associated with different factors. For the drought measured by Standard Precipitation Evaporation Index (SPEI), its variations are contributed by both precipitation and temperature. Due to the different sources of precipitation and temperature variations, the characteristics and factors of SPEI-measured droughts may depend upon the time scale and location of droughts in concern. In this talk, we will present an analysis of contributions of precipitation and temperature to the spatial patterns and temporal variations of drought with different durations over Asia measured by SPEI. Our results show that the SPEI displays a large component of trend, which is attributed to the contribution of the temperature trend. The 3-month SPEI (SPEI03) and 9-month (SPEI09) display a dominant dipole pattern and 24-month SPEI (SPEI24) displays a leading tripole pattern, all of which are related to both precipitation and temperature variations. The dipole pattern of SPEI24 is mainly due to temperature trend. The dipole (tripole) pattern of SPEI24 has a closer link to the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO), respectively.

Increased Variability of Western Pacific Subtropical High Under Greenhouse Warming

Kai YANG1, Wenju CAI2,3#+
1Chinese Academy of Sciences, China, 2Ocean University of China and Qingdao National Laboratory for Marine Science and Technology, China, 3Commonwealth Scientific and Industrial Research Organisation, Australia

An anomalous strengthening in western Pacific subtropical high (WPSH) increases moisture transport from the western equatorial Pacific to East Asia, inducing anomalous boreal summer monsoonal rainfall, causing extreme events in the densely populated region. Although such positive WPSH anomalies can be induced by anomalous warming in the Indian and/or the tropical Atlantic Ocean, the majority of the events develop concurrently with anomalous cold sea surface temperature (SST) in the central Pacific (CP) where an incipient La Niña occurs, promoting anomalous anticyclonic anomalies over the northwestern Pacific region. How variability of the WPSH might respond to greenhouse warming remains unclear. Using outputs from 32 latest climate models, here we find an increase in WPSH variability translating into a 73% increase in the frequency of strong WPSH events under a business-as-usual emission scenario supported by a strong inter-model consensus. Under greenhouse warming, the response of tropical atmosphere convection to CP SST anomalies increases, as does the response of the northwestern Pacific anticyclonic circulation. Thus, climate extremes such as floods in the Yangtze River Valley of East China associated with WPSH variability are likely to be more frequent and more severe.

Characterization of East Asian Rainbands and its Associated Circulation Over the Tibetan Plateau Region

Jiabin LIU, Inez FUNG, John CHIANG#+
University of California, Berkeley, United States

Rainbands that migrate northward from spring to summer are persistent features of the East Asian summer monsoon. This study employs a machine learning algorithm to identify individual East Asian rainbands from May to August in the 6-hourly ERA-interim reanalysis product, and captures rainband events during these months for the period 1979-2018. The median duration of rainband events at any location in East Asia is 12 hours, and the centroids of these rainbands move northward continuously from approximately 28°N in late May to approximately 33°N in July, instead of making jumps between quasi-stationary periods. While the length and overall area of the rainbands grow monotonically from May to June, the intensity of the rainfall within the rainband dips slightly in early June before it peaks in late June.  We explore circulation features associated with rainband formation through compositing of rainband days. Extratropical northerly winds on all pressure levels over East China are the most important anomalous flow accompanying the rainband events. The anomalous northerlies augment climatological background northerlies in bringing low moist static energy air and thus generate the front associated with the rainband. Persistent lower tropospheric southerly winds bring in moisture that feeds the rainband and are enhanced a few days prior to rainband events, but are not directly tied to the actual rainband formation.

AS03-A021 | Invited
Different Future Changes Between Early and Late Summer Monsoon Precipitation in East Asia

Hirokazu ENDO#+, Akio KITOH, Tomoaki OSE, Ryo MIZUTA
Japan Meteorological Agency, Japan

This study investigates future changes in East Asian summer monsoon (EASM) precipitation and the associated atmospheric circulation changes based on ensemble projections with a 60-km mesh atmospheric general circulation model (MRI-AGCM60). The projections at the end of the twenty-first century under the Representative Concentration Pathway 8.5 (RCP8.5) scenario indicate an overall increase in EASM precipitation but with large sub-seasonal and regional variations. In June, the Meiyu–Baiu rainband is projected to strengthen, with its eastern part (i.e., the Baiu rainband) shifted southward relative to its present-day position. This result is robust within the ensemble simulations. In July and August, the simulations consistently project a significant increase in precipitation over the northern East Asian continent and neighboring seas; however, there is a lack of consensus on the projection of the Meiyu–Baiu rainband in July. A small change in precipitation over the Pacific is another feature in August.
Results of sensitivity experiments with the MRI-AGCM60 reveal that the precipitation changes in early summer are dominated by the effects of sea surface temperature (SST) warming (i.e., uniform warming and the tropical pattern change), inducing an increase in atmospheric moisture and a strengthening and southward shift of the upper-level East Asian westerly jet (EAJ), especially over the Pacific. On the other hand, the influence of land warming and successive large SST warming in the extratropics is apparent in the precipitation changes in late summer. These late summer effects oppose and exceed the early summer effects through changes in the EAJ and low-level monsoon winds. These results suggest that the competition between the opposing factors makes the signal of the Meiyu–Baiu rainband response smaller in July than in June. Therefore, there tends to be a larger spread among simulations regarding the future tendency of the rainband in July.

Mon-01 Aug | 13:00 - 14:30 | MR01
AS02 - Climate Change and Tropical Climatic Hazards in Asia Oceania

Session Chair(s): Johnny CHAN, City University of Hong Kong

The Decadal Variation of Eastward-moving Tropical Cyclones in the South China Sea During 1980-2020

Xi LUO1+, Lei YANG2#, Sheng CHEN2, Dong LIANG1, Johnny CHAN3, Dongxiao WANG1
1Sun Yat-sen University, China, 2Chinese Academy of Sciences, China, 3City University of Hong Kong, Hong Kong SAR

The track of tropical cyclones (TCs) formed in the South China Sea (SCS) can be divided into eastward and westward directions. Significant decadal variation during 1980-2020 only exists in the number of eastward-moving TCs, especially during July-September, with 47% TCs moving eastward during 1994-2004 (Period II), 22% during 1980-1993 (Period I) and only 15% during 2005-2020 (Period III). This decadal change is related to the zonal shift of Western Pacific Subtropical High (WPSH). An eastward-retreated WPSH during 1994-2004 leads to upward motion and westerly flow anomaly over the northern SCS, and therefore favors TC genesis and eastward motion. The eastward-retreated WPSH is associated with a warm SST anomaly over the tropical western-central Pacific which induces a cyclonic flow and weakens the WPSH. With the weaker modulation of WPSH, stronger intraseasonal oscillation (ISO) in the SCS during Period II favors eastward-moving TCs due to the westerly flow associated with the ISO.

Changes in Tropical Cyclone-induced Extreme Hourly Precipitation Over China During 1975-2018

Yali LUO#, Baochen YANG+, Lu LIU, Xiaoling JIANG
Chinese Academy of Meteorological Sciences, China

This study analyzes the spatiotemporal distributions and climate trends of the TC-induced extreme hourly precipitation (EXHP) in the warm season (May-September) during 1975-2018 over China and the involved possible mechanisms. Each TC is classified as a high-, mid-, and low-EXHP TC according to the total number of EXHP it produces over China. Results show that low-EXHP TCs have a greater contribution to the total TC-induced EXHP over southern and southwestern China, whereas high-EXHP TCs make greater contributions over eastern and northeastern China as they tend to move northwestward after making landfall. It is shown that, although the total frequency of EXHP-producing TCs display a decreasing trend, the total frequency of TC-induced EXHP over China shows a significant increasing trend, which is largely contributed by the high-EXHP TCs. To explore the possible mechanisms responsible for the different characteristics in EXHP-producing TC groups, we further analyze the large-scale environmental conditions with respect to three groups by composite analysis. The cooperation of large-scale environmental fields between high- and low-levels provide favorable conditions for the intensification of TCs and the enhancement of the TC-induced precipitation for the high-EXHP group, such as stronger divergence at high-level, weaker vertical wind shear, more sufficient water vapor and more conducive steering airflow over the southeastern and eastern areas of mainland China. The westward and northward movement of western North Pacific subtropical high is conducive to the northward shift of TC tracks, thus contributing to the high frequency of TC-induced EXHP over the eastern area of mainland China.

Lightning Characteristics Over Shenzhen Area Induced By Tropical Cyclones

Qinglan LI#+, Chaoyi MA
Chinese Academy of Sciences, China

This paper studies the characteristics of lightning in Shenzhen under the influence of tropical cyclones. Using the historical data of tropical cyclones (TCs) in the Northwest Pacific Ocean from 2012 to 2019, the TCs within 1000 km to the Shenzhen National Meteorological Basic Station from 2012 to 2019 are screened and grouped according to the intensity of tropical cyclones. And using the lightning and temperature observation data in Shenzhen during the same period, the lightning characteristics induced by TCs with different intensity levels at various distances and azimuths in Shenzhen are studied. It is found that the inter-annual variation of lightning in Shenzhen under the influence of TCs is very large, and the lightning activity in Shenzhen is the most active in July and August in a year. Most of the distances where TCs have a great impact on lightning activities in Shenzhen are beyond 400 km. That means Shenzhen is in the outer rainband of TCs. Generally, during TCs’ season, TD, TS, and STS are more likely to cause lightning in Shenzhen, especially when TS is located in the Fujian area, 400-600 km away from Shenzhen. This article can provide scientific and technological references for TCs disasters prevention and mitigation in Shenzhen.

Developing a Tropical Cyclone Risk Assessment for Papua New Guinea

Cameron DO#+
Bureau of Meteorology, Australia

Tropical cyclones are devastating natural hazards that threaten lives, infrastructure and the environment. Impacts can be felt in the form of damaging winds, heavy sustained rainfall leading to flooding and landslides, as well as storm surges leading to coastal inundation. In recent years for the country of Papua New Guinea (PNG), tropical cyclones have taken lives, left people homeless and destroyed infrastructure as well as agricultural crops vital to the country’s economy. With a high percentage of their population situated in the highlands, many communities are susceptible to heavy rainfall hazards such as floods and landslides, while the rest of the population living near the coast are hit by cyclonic winds first and potential coastal inundation due to storm surge. This study collated provincial data on population characteristics, land use/cover, critical infrastructure, elevation, and economical output among other variables to build exposure and vulnerability indices for PNG. Combined with future projections of tropical cyclone hazard’s location and occurrence, a risk index was created. Results were displayed as a risk map, viewable in a web application allowing for a user-friendly interface to compare values and give a snapshot of spatial trends. Resultant trends are discussed in this study, as well as discussion of implications and suggestions for the future.

Mon-01 Aug | 13:00 - 14:30 | MR07
AS18 - Carbon Neutrality, Clean Air and Regional Interactions

Session Chair(s): Yingying YAN, China University of Geosciences

AS18-A014 | Invited
The Impact of Compound Extreme Weather Events on Ozone Pollution

Yang GAO#+
Ocean University of China, China

Ozone pollution has been a major air pollution issue since the mid-20th century, and it has been affected by a number of factors. Climate change is one of the primary drivers which may modulate the photochemical reaction rate, transport pathways as well as biogenic emissions. It is urgent to understand the regimes in the climate modulation on ozone formation and accumulation. Based on studies over United States and China, we aim to discuss the following questions in this talk. Firstly, the impact of compound extremes, i.e., co-occurrence of heat waves and atmospheric stagnation, on the ozone enhancement. Secondly, the synergic effect of anthropogenic emissions and biogenic emissions, particularly along the reduction of anthropogenic emissions, on ozone concentrations in typical ozone pollution prone regions such as North China. Lastly, the effect of temperature and water vapor on ozone. In particularly, their competing effects are interestingly delineated based on multi-year simulations. The messages delivered are believed to be useful in understanding the mechanism governing the ozone concentrations as well as providing information for policy markers in regard of ozone pollution control.

Impact of Eastern and Central Pacific El Niño on Lower Tropospheric Ozone in China

Zhongjing JIANG#+, Jing LI
Peking University, China

Tropospheric ozone is an essential atmospheric component as it plays a significant role in influencing radiation equilibrium and ecological health. It is affected not only by anthropogenic activities but also by natural climate variabilities. Here we examine the tropospheric ozone change in China associated with the Eastern Pacific (EP) and Central Pacific (CP) El Niño using satellite observations from 2007 to 2017 and GEOS-Chem simulations from 1980 to 2017. GEOS-Chem simulations reasonably reproduce the satellite-retrieved lower tropospheric ozone (LTO) changes despite a slight underestimation. Results show that El Niño generally exerts negative impacts on LTO concentration in China, except for southeastern China during the pre-CP El Niño autumn and post-EP El Niño summer. The budget analysis further indicates that for both events, LTO changes are dominated by the transport process controlled by circulation patterns and the chemical process influenced by local meteorological anomalies associated with El Niño, especially the solar radiation and relative humidity changes. The differences between EP and CP-induced LTO changes mostly lie in southern China. The different strengths, positions, and duration of western North Pacific anomalous anticyclone (WNPAC) induced by tropical warming are likely responsible for the different EP and CP LTO changes. During the post-EP El Niño summer, the Indian ocean capacitor also plays an important role in controlling LTO changes over southern China.

The Striking Effect of Vertical Mixing in the Planetary Boundary Layer on New Particle Formation in the Yangtze River Delta

Shangfei HAI1#+, Shiyi LAI2, Yang GAO1, Lifang SHENG1
1Ocean University of China, China, 2Nanjing University, China

New particle formation (NPF) induces a sharp increase in ultrafine particle number concentrations and potentially acts as an important source of cloud condensation nuclei (CCN). As the densely populated areas of China, the Yangtze River Delta region shows a high frequency of observed NPF events at the ground level, especially in spring. Although recent observational studies suggested a possible connection between NPF at the higher altitudes and the ground level, the role played by vertical mixing, particularly in the planetary boundary layer (PBL) is not fully understood. We integrate the measurements in Nanjing on 15-20 April 2018, and the NPF-explicit Weather Research and Forecast coupled with chemistry (WRF-Chem) model simulations to explore the effect of vertical mixing on NPF and CCN. Our results indicate that newly formed particles at the PBL top could be transported downward by vertical mixing as the PBL develops. A numerical sensitivity simulation by eliminating aerosol vertical mixing suppresses both the downward transport of particles formed at a higher altitude and the dilution of particles at the ground level. The resulting higher Fuchs surface area at the ground level, together with the lack of downward transport, yields a sharp weakening of NPF strength and delayed start of NPF therein. The vertical mixing, therefore, leads to a more than double increase of surface particle number concentration in the 10-40nm (CN10-40) and a one-third decrease of the PBL top CN10-40. The continuous growth of nucleated ultrafine particles at the PBL top is strongly steered by the upward transport of condensable gases, with close to half increase of particle number concentrations in Aitken mode and CCN at a supersaturation rate of 0.75%. The findings may bridge the gap in understanding the complex interaction between PBL dynamics and NPF events, reducing the uncertainty in assessing the climate impact of aerosols.

Sulfate and Nitrate Elevation in Reverse-transport Dust Plumes Over Coastal Areas of North China

Wenshuai LI1#+, Yuxuan QI1, Wen QU2, Wenjun QU1, Jinhui SHI1, Daizhou ZHANG3, Yingchen LIU1, Yuanyuan MA1, Yanjing ZHANG1, Danyang REN1, Xueqing DU1, Shishi YANG1, Xinfeng WANG4, Li YI1, Xiaomei GAO5, Lifang SHENG1, Yang ZHOU 1
1Ocean University of China, China, 2North China Sea Marine Forecasting Center of State Ocean Administration, China, 3Prefectural University of Kumamoto, Japan, 4Shandong University, China, 5University of Jinan, China

Sulfate and nitrate formed on dust aerosols can considerably affect particles’ physicochemical properties due to their high hygroscopicity. Dust reverse-transport (DRT) events may occur in eastern China when the trajectory of the dust plume undergoes a distinct turn caused by Asian highs or cyclones, resulting in the re-appearance of the dust plume in the same place but with the altered chemical composition caused by anthropogenic pollutants mixed in. In this study, three DRT events were identified in Qingdao, a coastal city of North China. The secondary sulfate and nitrate in PM2.5 collected during the DRT events were estimated according to the mass concentration of water-soluble ions and dust tracer metal. Several key factors, including heterogeneous reactions on aerosols, photochemical conversions in the air, and precursors’ abundance in dust plumes, affect the aging of dust plumes. In the presence of adequate ammonium, high-level precursors and oxidants in the air, sulfate and nitrate were efficiently produced under moderate/high humidity conditions during the DRT period. Compared with the first dust arrival stage, the concentration of sulfate and nitrate increased 0.7–3.4 and 6.7–13.2 fold, respectively, in 48 hours since the DRT occurrence. In contrast, when the relative humidity and the molar ratio of [NH4+]/[SO42−] were low, the growth of sulfate and nitrate was negligible in dust plumes. This study reveals that the efficiency of sulfate and nitrate formation in dust plumes is closely related to the atmospheric properties along the transport pathway.

The Development of a High-resolution Biogenic Emission Inventory From Urban Green Spaces in China

Mingchen MA#+, Yang GAO
Ocean University of China, China

Biogenic volatile organic compounds (BVOCs), the largest source of VOCs emissions globally, play vital roles in modulating atmospheric chemistry and the formation of ozone and secondary organic aerosol (SOA). A large number of studies have quantified BVOC emissions in the past. However, the source of BVOC emissions in the urban areas, urban green space BVOC (U-BVOC) emissions, is largely neglected due to relatively coarse landcover type data, but also because their important contribution to urban BVOCs was previously unrecognized. In this study, the first BVOC emission inventory emitted by urban green spaces in China was developed based on an ultra-fine landcover dataset at a spatial resolution of 10-m. This U-BVOC emission inventory has a spatial resolution of 27 km, while a high resolution of 1 km is applied in areas with dense U-BVOC emissions, such as the North China Plain, the Yangtze River Delta, and the Pearl River Delta. The new U-BVOC emission inventory shows that nationwide U-BVOC emissions account for only 0.1% of natural BVOC emissions, but they could account for a large fraction of total BVOC emissions in megacities. In particular, the interannual variability in developed regions such as the North China Plain fits well with recent ozone trend changes, emphasizing its potential key role in driving ozone formation. Considering that the U-BVOC emissions emit directly in the core urban area and their high emission intensity, the construction and continuous improvement of the U-BVOC emission inventory may support the understanding of ozone and SOA formation.

Mon-01 Aug | 13:00 - 14:30 | MR08
AS14 - Machine Learning in Weather, Climate and Hydrological Analysis and Predictions

Session Chair(s): Venkata Ratnam JAYANTHI, Japan Agency for Marine-Earth Science and Technology, Rajib MAITY, Indian Institute of Technology Kharagpur

Constraining Rainfall Bias in Thailand Using Partial Convolutions

Kiyoharu HASEGAWA#+, Shinjiro KANAE
Tokyo Institute of Technology, Japan

Thanks to their remarkable development, numerical models have shown high prediction accuracy in short-term rainfall forecasting. On the other hand, in regions where rainfall is closely related to complex meteorological phenomena such as monsoon including tropical regions, there is still a large uncertainty. Deep learning, a powerful statistical method, can learn spatial characteristics and supplement missing values from surrounding data. Applying this method, we propose a method to reproduce rainfall distribution in the tropics from surrounding rainfall information. Using the CMIP6 rainfall dataset, rainfall in regions other than the entire northern region of Thailand is learned from 65 ensembles of global rainfall data, and the model outputs rainfall within the entire northern region. The results showed that the deep learning model tended to overestimate the actual rainfall, but was able to accurately reproduce the rainfall distribution. This method is expected to be applied in practice because of its low computational cost and limited data requirements. It also has the potential to be applied to global regions.

Model-consistent Parameterisation With Deep Learning and Differentiable Physics

Yongquan QU#+, Xiaoming SHI
Hong Kong University of Science and Technology, China

Numerical simulations are the backbone of today's weather forecast and climate projections. Yet due to the ubiquitous turbulence in the atmospheric boundary layer and convective systems, directly resolving all meaningful dynamic scales is prohibiting with current computational capacity. Thus, numerical models run on relatively low-resolution grids and represent sub-grid scale (SGS) processes with parameterization. Traditional turbulence parameterization schemes are built on heuristic assumptions and sometimes tuned without coupling with the dynamic core or other physical parameterizations, therefore in some weather and climate regimes, they exhibit considerable uncertainties and low-fidelity. The development of machine learning (ML) techniques enables the feasibility of data-driven parameterizations, which has been investigated in a lot of studies. Some results suggested that a priori trained ML models perform poorly when they are coupled to dynamic cores and tested. Here we use the evolution of shear instability in a barotropic vorticity equation (BVE) model with a periodic forcing as a prototype problem to develop a model-consistent training strategy, which employs a numerical solver with automatic differentiation and includes it in the loss function. This approach enables the interaction between the dynamic core and the deep learning parameterization during the training phase. Our training set contains only a short period of coarsened high-resolution simulations, but the trained model, given an initial condition long after the training set time, is still able to significantly improve the prediction lead time compared to the low-resolution simulations with or without a Smagorinsky turbulence model. We also investigated the incorporation of attention mechanism and covariance matrix, in our deep learning model to extend the forecast lead time. By conducting transfer learning using a limited number of observations, our model’s performance is further improved. This study demonstrates a potential pathway to use machine learning for enhancing the prediction skills of our climate and weather models.

Predicting Surface Air Maximum Temperature Over India at Medium-range Time Scale Using Machine Learning Techniques

Venkata Ratnam JAYANTHI#+, Swadhin BEHERA, Masami NONAKA, Patrick MARTINEAU , Kalpesh PATIL
Japan Agency for Marine-Earth Science and Technology, Japan

Surface air maximum temperature over India in the months March to June, the season of heat waves, is predicted using machine learning techniques at a lead time of 10-days (medium-range time scale). Lag correlation between the observed surface air maximum temperature and sea surface temperature as well as soil moisture was used to derive the input attributes for the models. The results indicate the predictions of the Bagging regressor with Multi-layer Perceptron as the base estimator to have higher anomaly correlation skill score along with higher hit rates and lower false alarm rates compared to several other machine learning techniques. The results of the study would be helpful to the society as a whole.

Mon-01 Aug | 13:00 - 14:30 | MR04
AS06 - Mesoscale Meteorology and High-impact Weather

Session Chair(s): Chung-Chieh WANG, National Taiwan Normal University, Tieh-Yong KOH, Singapore University of Social Sciences

A Fast, Physically Based Model for Predicting Long-range Firebrand Transport in Bushfire Plumes

Jeff KEPERT1,2#+, Kevin TORY2, Will THURSTON3
1Bureau of Meteorology Research, Australia, 2Bureau of Meteorology, Australia, 3Met Office, United Kingdom

Recent years have seen a rapid increase in wildfire behaviour and damage in areas including Australia, the United States, Canada and Europe. Meteorology, on all scales, plays a major role in setting the conditions for, and modulating the short-term behaviour of, catastrophic wildfires. Spotfires are a one of many major problems in bushfire management, and in extreme circumstances have been observed to ignite new fires over 30 km ahead of the parent fire. Spotfires result from firebrands transported from the fire plume igniting fuel well ahead of the front. They greatly complicate suppression efforts, contribute to fires breaking control lines, and are implicated in structure loss. Existing forecast techniques provide insufficient guidance on the problem of long-range spotting, and the meteorological and fire conditions that lead to such events are not well understood. We present a computationally inexpensive, physically based model of firebrand transport within bushfire plumes, with four components: an integral plume model, a model of turbulence within the plume, a probabilistic model of firebrand transport within the plume, and a model of transport beneath the plume. The predicted firebrand landing distributions from this model compare satisfactorily to the explicit transport calculations of Thurston et al. (2017). We examine the sensitivity of the simple model to its input parameters. The 90th percentile of spotting distance increases with increasing fire power and decreases with increasing firebrand terminal fall velocity and fire radius. Where there is a meteorological inversion and the plume updraft is sufficiently strong to carry firebrands that high, the inversion substantially limits the transport distance, with increased inversion height favouring longer-range transport. The effect of wind speed is complex, due to the competing factors of faster horizontal transport but suppressed vertical plume development with stronger winds.

A Large-eddy Simulation Study of Deep-convection Initiation Through the Collision of Two Sea-breeze Fronts

Shizuo FU1#+, Richard ROTUNNO2, Jinghua CHEN3, Xin DENG4, Huiwen XUE4
1Fujian Normal University, China, 2National Center for Atmospheric Research, United States, 3Nanjing University of Information Science & Technology, China, 4Peking University, China

Deep convection plays important roles in producing severe weather and regulating the large-scale circulation. However, deep-convection initiation (DCI), which determines when and where deep convection develops, has not yet been fully understood. Here, large-eddy simulations are performed to investigate the detailed processes of DCI, which occurs through the collision of two sea-breeze fronts developing over a peninsula. In the simulation with a maximum total heat flux over land of 700 or 500 W m-2, DCI is accomplished through the development of three generations of convection. The first generation of convection is randomly produced along the colliding sea-breeze fronts. The second generation of convection only develops in regions where no strong downdrafts are produced by the first generation of convection and is also mainly produced through the collision of the sea-breeze fronts. The third generation of convection mainly develops from the intersection points of the cold pools produced by the second generation of convection and is produced through the collision between the gust fronts and the sea-breeze fronts. Decreasing the maximum total heat flux from 700 to 500 W m-2 weakens each generation of convection. Further decreasing the maximum total heat flux to 300 W m-2 leads to only one generation of shallow convection.

Generation of Multiple Gravity Wave Couplets by Latent Heating Forcing and Mechanical Oscillators During Convection

Hongpei YANG+, Yu DU#
Sun Yat-sen University, China

Convectively generated low-frequency gravity waves had been found to be greatly coupled with the initialization and development of convection. During convection, alternating wavy pattern of updrafts and downdrafts propagating in the troposphere were recorded. Idealized numerical simulations were performed to examine their generation and figure out how thermal and dynamical forcing may play the role. Moist experiments show that latent heating emerges as a nonnegligible contributor to the generation of gravity waves but cannot fully explain the appearance of multiple wave couplets even under a cyclical-like redevelopment. Spectral analyses of the vertical velocity fields identify gravity wave with similar horizontal phase speed varying from the speed of the second-order (19 m s-1) and the first-order (38 m s-1) gravity wave modes, but two different spectrum centers that approximately match latent heating and Brunt-Väisälä frequency at the level of neutral buoyancy (LNB), respectively. Dry experiments with prescribed latent heating further prove that the net buoyancy can force convective updrafts to oscillate around the LNB, and thus initiate wave couplets both in the troposphere and lower stratosphere. Sensitivity experiments show that a much higher model lid, or a strong and deep damping layer may exert influence on wave amplitudes through weakening the overshooting updrafts, which means a much weaker effect of the mechanical oscillator mechanism.

Mon-01 Aug | 13:00 - 14:30 | MR05
AS17 - Regional Climate Downscaling and Cordex: Challenges and Prospects

Session Chair(s): Jason EVANS, University of New South Wales

A Comparative Study of Various Downscaling and Bias Correction Methods for Future Changes of Precipitation Over the Indonesian Region

Motoki NISHIMORI1#+, Michihiko TONOUCHI2, Hiroshi SATODA2, Kadarsah 3, Agus SABANA HADI3, Dodo GUNAWAN3
1National Agriculture and Food Research Organization, Japan, 2Japan Meteorological Business Support Center, Japan, 3Agency for Meteorology, Climatology and Geophysics, Indonesia

The climate of Indonesia located under the equator is predominated by the monsoon of both northern and southern hemispheres. Climate changes in Indonesia would affect not only agricultural production but also the whole economy. The future climate changes were projected by GCM simulation, but the geographical features of Indonesia are very complicated. Therefore, various downscaling methods involving RCM simulations are necessary to find detailed changes in the monsoon climate over Indonesia. In this study, we aim to clarify the future climate change mainly of Java Island. Various types of bias correction (BC) methods combined with the statistical downscaling/spatial disaggregation (SD) method are applied to the output of CMIP5 GCMs. The seasonal change and amount of rainfall derived from CMIP5-GCMs were different from the observed one, but both GSA (Gaussian Scaling Analysis) and CDFDM (Cumulative Distribution. Function-based Downscaling Method) have well captured the seasonal characteristics of the observed climate. Though the future tendencies of precipitation changes (RCP8.5; 2041-2060) are different in each month, generally decreasing in the onset season and increasing in the dry season. There is a general coincidence that precipitation at the onset of the monsoon is likely to decrease in the future, but the trend of precipitation change may differ from that of the GCM itself depending on the BC method.

Dynamic Downscaling for River Basins in Philippines and Indonesia

Tomoki USHIYAMA1,2#+
1Public Works Research Institute, Japan, 2National Graduate Institute for Policy Studies, Japan

To assess the flood and drought risk change by global warming, dynamic downscaling was conducted for the Davao River basin, Philippines (7.5 N), and the Solo River basin, Indonesia (7.5S). The Meteorological Research Institute-Atmospheric General Circulation Model (MRI-AGCM) ver. 3.2S (super high resolution) and 3.2H (high resolution), with horizontal resolution of 20 km and 60 km, respectively, were downscaled into 5 km horizontal resolution by WRF model. We faced difficulty in reproducing realistic rainfall phenomena or appearance of rainfall frequency. Both of target regions with 7.5 degrees latitude, north and south, are close to the equator. Therefore, tropical cyclones have rarely generated in those regions. However, downscaling with adopting cumulus parameterization schemes, such as Kain & Fritsch scheme, generated too many tropical cyclones, even the GCM didn’t generate tropical cyclones. When we downscaled without cumulus parameterization schemes with a single frame of 5 km horizontal resolution, we got better representation of tropical cyclone generation as well as the frequency of rainfall appearances. In the Solo River basin, Indonesia, the MRI-AGCM and its downscaled rainfall in wet season is likely to increase in the end of 21st century in RCP8.5 scenario, while CORDEX-SEA downscaling showed decreasing trend. Our downscaled rainfall in the Davao River basin, Philippines, also showed increasing trend in the end of 21st century in RCP8.5 in wet season, whereas CORDEX-SEA downscaling showed decreasing trend. Careful discussion is required to handle this uncertainty and to plan for getting more robust results.

Models Performances and Projected Precipitations Based on the CMIP5 5 KM Regional Climate Downscaling Simulations Over Peninsular Malaysia

Jing Xiang CHUNG1, Fredolin TANGANG2,3#+, Jerasorn SANTISIRISOMBOON4, Liew JUNENG2, Ester SALIMUN2, Abdul Azim AMIRUDIN2, Mohd Syazwan Faisal MOHD5, Mohd Fadzil MOHD AKHIR1, Faye Abigail CRUZ6, Julie Mae DADO6, Thanh NGO-DUC7, Phan VAN-TAN8
1Universiti Malaysia Terengganu, Malaysia, 2National University of Malaysia, Malaysia, 3Ramkhamhaeng University, Thailand, 4Ramkhamhaeng University Center of Regional Climate Change and Renewable Energy (RU-CORE), Thailand, 5National Hydraulic Research Institute of Malaysia, Malaysia, 6Manila Observatory, Philippines, 7University of Science and Technology of Hanoi, Viet Nam, 8Vietnam National University, Viet Nam

Further downscaling into the 5 km resolution of the CORDEX Southeast Asia (CORDEX-SEA) 25 km resolution simulations has been implemented using the Regional Climate Model version 4.7 (RegCM4.7) over a subdomain covering the Peninsular Malaysia. There CORDEX-SEA simulations that were forced with EC-EARTH, MPI-ESM-MR and HadGEM2-ES from future emission scenarios of RCP4.5 and RCP8.5 were considered. We used the MIT Emanuel cumulus parameterization scheme (CPS) over the land and Kain-Fritsch over the ocean, and the CLM4.5 for land surface scheme were used in the 5 km simulations. Performance analysis indicated added values in the 5km simulations of precipitation. The 5km simulations were successfully able to simulate the detailed east-west contrast of the DJF rainfall, the north-south contrast of SON rainfall. The biases were much reduced in the 5km simulations. The annual cycles from the 5 km simulations were closer to the observations. The superior performances of the 5km simulations may not necessarily due to the resolution but can be contributed schemes. The projected precipitation showed that a drying tendency over the rest of the 21st century regardless of the seasons. For precipitation extreme indices such as Rx1day, an increase in DJF Rx1day is projected in the early century under RCP4.5 but to decrease gradually for the rest of the 21st century. For RCP8.5 scenario, the DJF Rx1day was projected to decrease except over the central part of Peninsular Malaysia. For JJA, under both scenarios, a decrease in Rx1day was projected throughout the 21st century. For consecutive dry days (CDD), both RCP scenarios are projected to increase for both JJA and DJF seasons. These overall drying trends appear consistent with the 25 km simulations. However, despite improvements in the 5km simulations, the projections have no uncertainty component estimation of different regional climate models.

Performance of the Convective Permitting Non-hydrostatic Regional Climate Model (NHRCM) in Simulating the Rainfall Over Peninsular Malaysia

Jing Xiang CHUNG1, Fredolin TANGANG2,3#+, Hidetaka SASAKI4, Akihiko MURATA4, Jerasorn SANTISIRISOMBOON5, Liew JUNENG2, Sheau Tieh NGAI2, Ester SALIMUN2, Mohd Fadzil MOHD AKHIR1
1Universiti Malaysia Terengganu, Malaysia, 2National University of Malaysia, Malaysia, 3Ramkhamhaeng University, Thailand, 4Japan Meteorological Agency, Japan, 5Ramkhamhaeng University Center of Regional Climate Change and Renewable Energy (RU-CORE), Thailand

This study used the Non-Hydrostatic Regional Climate Model (NHRCM) developed by the Japan Meteorological Research Institute (MRI) to simulate the rainfall over Malaysia. The resolution of the model was 2km and it was a convective-permitting model. A simulation from September 1979 until October 2003 was carried out to represent the historical period climate. The forcing data used to drive the NHRCM (NHRCM02) was the 5km × 5km downscaled MRI-AGCM3.2 output (NHRCM05). The simulated seasonal rainfall climatology showed that NHRCM02 had a greater success than NHRCM05 in reproducing the east-west and north-south rainfall contrast for DJF and SON season, respectively. The convective permitting NHRCM02 had the advantage over the cumulus parametrization scheme governed NHRCM05 during the seasons where rainfall was active, but not so much when the rainfall was less active, such as MAM and JJA. In addition, for NHRCM02 the rainfall seasonal biases were much smaller than that of NHRCM05, except for DJF over the east coast of PM, where the wet rainfall bias is much stronger than that of NHRCM05. The seasonal rainfall distribution produced by NHRCM02 matched better the observation than that of NHRCM05. This is due to NHRCM02 that has the tendency to produce more heavy rainfall which was greatly being underestimated by NHRCM05. In terms of rainfall annual cycle, both NHRCM simulations were able to capture the signature bimodal and unimodal pattern for both west and east coast of PM respectively. However, the simulations noticeably overestimated the first rainfall peak over the west coast during MAM. Over the east coast, NHRCM02 tended to overestimate the rainfall from December to May, but closely matched that of observation from June till November. For NHRCM05 on the other hand, the simulation generally underestimated the rainfall throughout the year except during January to April.

A High-resolution Climate Experiment Over Part of Vietnam and the Lower Mekong Basin: Performance Evaluation and Projection for Rainfall

Thanh NGO-DUC1#+, Huy HOANG-CONG2, Tuyet THI3, Long TRINH-TUAN4, Jing Xiang CHUNG5, Phan VAN-TAN6, Fredolin TANGANG7, Jerasorn SANTISIRISOMBOON8
1University of Science and Technology of Hanoi, Viet Nam, 2Ministry of Natural Resources and Environment, Viet Nam, 3Ministry of Planning and Investment, Viet Nam, 4Tokyo Metropolitan University, Japan, 5Universiti Malaysia Terengganu, Malaysia, 6Vietnam National University, Viet Nam, 7Universiti Kebangsaan Malaysia, Malaysia, 8Ramkhamhaeng University Center of Regional Climate Change and Renewable Energy (RU-CORE), Thailand

This study first evaluates the performance of three model experiments in representing rainfall over part of Vietnam and the Lower Mekong Basin for the historical period 1986–2005. The three experiments include the Coupled Model Intercomparison Project Phase 5 (CMIP5) EC-EARTH Global Climate Model (GCM) and two downscaling runs based on a regional climate model at 25km resolution with the GCM forcing (RCM-25km) and at 5km resolution with the RCM-25km forcing (RCM-5km). Verifications against observations show that the experiments generally capture the spatial distribution of climatological rainfall. While the GCM well represents the observed average rainfall cycles, its coarse resolution limits its capability in reproducing extreme rainfall values. The downscaling experiments do not clearly show their advantage in simulating average rainfall but exhibit significant added values when representing extreme rainfall in the study region. The RCM-5km does not outperform its driving 25km experiment in representing the mean and extreme rainfall values, suggesting that having a better resolution may not compensate for having a good model configuration with appropriate physical schemes. Analysis of climate projection for the far future period 2080–2099 under two representative concentration pathways (RCP) scenarios, RCP4.5 and RCP8.5, reveals that the downscaling experiments can modify the change direction of future rainfall obtained with the GCM. While the EC-EARTH GCM generally projects wetter tendencies of up to 50%, the downscaling experiments project a general decrease of down to -50% under both scenarios over the study domain. Regarding extreme rainfall, the annual maximum 1-day rainfall amount (RX1day) is projected to increase for the three experiments. The simple daily intensity index (SDII) future changes follow those of the annual rainfall values.

Variability Characteristics and Mechanism of Extreme Events in South Asian Monsoon Region Under Changing Climate

Jerasorn SANTISIRISOMBOON1#+, Jaruthat SANTISIRISOMBOON1, Waranyu WONGSEREE2, Damrongrit SETSIRICHOK2, Patama SINGHRUCK3, Ratchanan SRISAWADWONG1, Fredolin TANGANG4,5, Liew JUNENG4, Jing Xiang CHUNG6, Phan VAN-TAN7, Thanh NGO-DUC8, Faye Abigail CRUZ9, Julie Mae DADO9
1Ramkhamhaeng University Center of Regional Climate Change and Renewable Energy (RU-CORE), Thailand, 2King Mongkut's University of Technology North Bangkok, Thailand, 3Chulalongkorn University, Thailand, 4National University of Malaysia, Malaysia, 5Ramkhamhaeng University, Thailand, 6Universiti Malaysia Terengganu, Malaysia, 7Vietnam National University, Viet Nam, 8University of Science and Technology of Hanoi, Viet Nam, 9Manila Observatory, Philippines

The study of variability characteristic and mechanism of extreme events in the South Asian Monsoon region under changing climate comprises 3 major activities including i) the analyses of extreme events over the area of Thailand and Southeast Asia in the historical period or 1970 – 2005 as well as the future projection up to the end of the century under two climate change scenarios, RCP4.5 and RCP8.5, ii) the analyses of the standard precipitation index and iii) the analyses of the correlation between the monsoon onset and climate variables as well as the impacts of climate change on monsoon onset, monsoon withdrawal and extreme indices. The high-resolution climate dataset from the downscaling of 3 GCMs of the Coupled Model Intercomparison Project phase 5 (CMIP-5) of Southeast Asia Regional Climate Downscaling (SEACLID)/CORDEX Southeast Asia Project from the historical period to the future projection was applied for the analyses. The results show that the maximum 1-day and 5 days precipitation total tends to increase as well as heavy precipitation day. This reflects the tendency of flash flood from heavy and very heavy precipitation. However, the annual precipitation total tends to decrease reflecting the signal of drought under the future climate change. Under the future climate change scenarios, the northeastern and southern regions tend to have higher drought impacts than other regions of Thailand. The results also show the impacts of future climate change on the Southeast Asia in terms of drought. The area over the peninsula and islands of Southeast Asia will have higher impacts from drought while the flash flood will be lower. The future climate change tends to affect the delay of monsoon onset and early withdrawal. The annual precipitation total tends to decrease with the shorter period of monsoon season.

Impacts of Planetary Boundary Layer Parameterization in RegCM4.7 on the Intensity and Structure of Simulated Tropical Cyclones Over the Philippines

Rochelle CORONEL1#+, Ma. Cathrene LAGARE2, Faye Abigail CRUZ3, Gemma NARISMA3, Marcelino VILLAFUERTE II4, Jennifer TIBAY3
1Ateneo de Davao University, Philippines, 2Tohoku University, Japan, 3Manila Observatory, Philippines, 4Philippine Atmospheric Geophysical and Astronomical Services Administration, Philippines

The impacts of planetary boundary layer (PBL) parameterizations on tropical cyclone (TC) climatology over the Philippine region is investigated using the RegCM4.7. The findings suggest that the University of Washington (UW) scheme in RegCM4.7 reproduced better count and distribution of TC intensity, including more intense TCs, and stronger wind and thermodynamic structures than the Holtslag scheme. Results show that downscaling ERA-Interim to 25-km resolution has improved the number of detected TCs in the RegCM simulations. The UW scheme simulated a TC count (380 TCs) nearest to the observation (376 TCs) with an increased number of moderate (Category 2 and 3) and strong (≥ Category 4) TCs than the Holtslag scheme (343 TCs) and ERA-Interim reanalysis (96 TCs). A composite analysis on the radial cross-section of the simulated winds shows that the UW parameterization generates stronger wind circulations with narrower and elevated maximum tangential winds in comparison with the Holtslag scheme. UW also enhances low-level momentum convergence and heating inside the radius of the maximum wind (RMW). The radial positioning of the strong diabatic heating of UW simulation within the RMW also supports the needed conditions for warmer core formation, and hence higher intensity TCs.

Mon-01 Aug | 13:00 - 14:30 | MR06
AS01 - Passive and Active Sensing of the Chemistry and Dynamics of the Middle and Upper Atmosphere

Session Chair(s): Iain REID, ATRAD Pty. Ltd., Patrick ESPY, Norwegian University of Science and Technology

Climatology of Interhemispheric Mesopause Temperatures Using the High- and Middle-latitude Meteor Radars

Wen YI1#+, Xianghui XUE1, Iain REID2,3, Damian MURPHY4, Masaki TSUTSUMI5, Chris HALL6
1University of Science and Technology of China, China, 2ATRAD Pty. Ltd., Australia, 3University of Adelaide, Australia, 4Australian Antarctic Division, Australia, 5National Institute of Polar Research, Japan, 6University of Tromsø, Norway

We present the climatology of mesopause temperatures using high- and middle-latitude meteor radars. The daily mesopause temperatures are estimated using ambipolar diffusion coefficient data from the meteor radars at Davis Station (68.6°S, 77.9°E), in Antarctica, Svalbard (78.3°N, 16°E), Tromsø (69.6°N, 19.2°E) in the Arctic, and Mohe (53.5°N, 122.3°E) and Beijing (40.3°N, 116.2°E) in the northern middle latitudes. The seasonal variations in the meteor radar-derived temperatures are in good agreement with the temperatures from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the TIMED satellite. Interhemispheric observations indicate that the mesopause temperatures over the southern and northern polar regions show a clear seasonal asymmetry. The seasonal variations in the Davis Station meteor radar temperatures in the southern polar mesopause are dominated by an annual oscillation (AO) with a relatively weak semiannual oscillation (SAO), which shows a clear minimum during summer and a maximum during winter. The mesopause temperatures in the northern high and middle latitudes observed by the Svalbard, Tromsø, Mohe and Beijing meteor radars mainly show an AO, with a maximum during winter and a minimum during summer. The AO in the northern polar regions is stronger than that in the southern polar regions, while the SAO in the southern polar regions is relatively strong compared to that in the northern polar regions.

Comparison of Mesospheric Wind Observed by the Monostatic and Bistatic Meteor Radars

Jie ZENG#+, Wen YI, Xianghui XUE
University of Science and Technology of China, China

All-sky meteor radars have been a widely used technique to investigate the mesosphere and lower thermosphere (MLT) region. In this study, we present a comparison of simultaneous horizontal winds observed by multistatic meteor radar system using the forward scatter and backscatter models. The mesospheric wind using the forward scatter model was observed by a link consisting of a monostatic meteor radar in Mengcheng (116.49 °E, 33.36 °N) and bistatic Changfeng receiver (117.223 °E, 31.982°N), separated by approximately 167 km. The mesospheric wind using backscatter model was observed by two co-located (about 300 m apart) meteor radars in Kunming (25.6°N, 103.8°E), but with different operating frequency. In order to test the performance between the forward and back scatter meteor radars, the meteor echoes are selected according to the arrival time and the location region. Our results demonstrate highly consistency of both monostatic and multistatic meteor radars and the more accurate multistatic results.

Investigation of Direct Solar Proton Impact on Arctic Stratospheric Ozone

Jia JIA1#+, Antti KERO2, Niilo KALAKOSKI3, Monika SZELAG3, Pekka T. VERRONEN2,3
1Norwegian University of Science and Technology, Norway, 2University of Oulu, Finland, 3Finnish Meteorological Institute, Finland

Recent studies reported up to a 10 % average decrease of lower stratospheric ozone at ∼ 20 km altitude following solar proton events (SPEs), based on superposed epoch analysis (SEA) of ozonesonde anomalies. Our study uses 49 SPEs that occurred after the launch of Aura MLS (2004–now) and 177 SPEs that occurred in the WACCM-D (Whole Atmosphere Community Climate Model with D-region ion chemistry) simulation period (1989–2012) to evaluate Arctic polar atmospheric ozone changes following SPEs. At the mesospheric altitudes a statistically significant ozone depletion is present. At the lower stratosphere (<25 km), SEA of the satellite dataset provides no solid evidence of any average direct SPE impact on ozone. In the individual case studies, we find only one potential case (January 2005) in which the lower-stratospheric ozone level was significantly decreased after the SPE onset (in both model simulation and MLS observation data). However, similar decreases could not be identified in other SPEs of similar or larger magnitude. We find a very good overall consistency between WACCM-D simulations and MLS observations of SPE-driven ozone anomalies both on average and for the individual cases, including case in January 2005.

AS01-A024 | Invited
MATS Satellite Data: How Well Can We Determine Gravity Wave Parameters?

Björn LINDER1#+, Peter PREUSSE2, Qiuyu CHEN2, Manfred ERN2, Linda MEGNER1, Jörg GUMBEL1, Erich BECKER3
1Stockholm University, Sweden, 2Forschungszentrum Jülich, Germany, 3NorthWest Research Associates, United States

MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is an upcoming Swedish satellite mission designed to investigate atmospheric waves in the Mesosphere and lower Thermosphere by imaging variations in O2 atmospheric band airglow emission between 70 and 110 km, as well as structures in Noctilucent clouds (NLC, PMSE). Performing a tomographic analysis of these images, 3D reconstruction of waves can be done, allowing the MATS mission to provide global properties of atmospheric waves in all spatial dimensions. In this talk we study the capabilities of the MATS gravity wave parameter retrieval, by analysing synthetic satellite data composed from HIAMCM (The High Altitude Mechanistic general Circulation Model) output. 

Record-breaking Stratospheric Smoke Events in Canada 2017, Siberia 2019, and Australia 2019/2020! Any Influence of Smoke Occurrence on Ozone Depletion and Cirrus Clouds?

Kevin OHNEISER1#+, Albert ANSMANN1, Ronny ENGELMANN1, Boris BARJA2, Holger BAARS1, Patric SEIFERT1, Hannes GRIESCHE1, Martin RADENZ1, Julian HOFER1, Dietrich ALTHAUSEN1, Cristofer JIMENEZ1
1Leibniz Institute for Tropospheric Research, Germany, 2University of Magallanes, Chile

Since 2017 we monitored three major stratospheric smoke events: A record-breaking western Canadian wildfire smoke amount was observed over Europe for more than 5 months in 2017, strong smoke pollution originating from extreme Siberian forest fires in July and August 2019 was observed with lidar over the High Arctic for more than 7 months (aboard the German ice breaker Polarstern during the MOSAiC expedition 2019-2020), and, in 2020 and 2021, we monitored the stratospheric perturbation by smoke with lidar over Punta Arenas, in southern Chile, originating from record-breaking Australian bushfires, for two years. Large amounts of biomass-burning smoke were lifted into the stratosphere and formed 5-15 km thick aerosol layers from the tropopause up to around 20 km and partly even 30 km height. The smoke particles influenced the Earth’s radiative balance, the dynamics of the atmosphere, ozone depletion in the Arctic and Antarctica, and the evolution of cirrus clouds in the upper troposphere via heterogeneous ice nucleation in which aged smoke particles served as ice-nucleating particles. The fact that the Siberian smoke event and the Australian smoke event coincided with record-breaking ozone hole events in both hemispheres motivated us to discuss a potential impact of the smoke particles on the strong ozone depletion. The discussion is based on the overlapping height ranges of the smoke layers, polar stratospheric clouds, and the ozone hole regions. We will discuss our long-term lidar observations of the three major smoke events with focus on the High Arctic and Punta Arenas observations, we will further present ozone profiles measured during the hemispheric spring seasons in 2020 to illuminate the potential impact of smoke on ozone depletion, and finally we will show cases with clear signs of smoke-cirrus interaction in the High Arctic as well as over the southernmost tip of South America.

Mon-01 Aug | 13:00 - 14:30 | MR03
AS07 - Asian Paleo-monsoon: Reconstructions and Simulations

Session Chair(s): Weiyi SUN, Nanjing Normal University

AS07-A012 | Invited
A Synthesis of Regional Paleoclimate Variations in China During the Past ~21 Ka

Huayu LU1#+, Yan ZHAO2, Xiangdong YANG2, Haibin WU2, Cheng ZHAO1, Enlou ZHANG2, Feng SHI2, Xueyuan KUANG1, Jingjing WANG1, Jun CHENG3, Zhengtang GUO2
1Nanjing University, China, 2Chinese Academy of Sciences, China, 3Nanjing University of Information Science & Technology, China

We use multiple proxies, including pollen, diatom and phytolith assemblages from various archives such as lake sediments, peats and paleosols distributed in different parts of China, to quantitatively and semi-quantitatively reconstruct paleoclimate changes in monsoonal and arid areas over the past ~21 ka. Our data show a significant variability in both monsoonal and arid regions. Comparing with modern observational data between 1961 and 1990, the annual and seasonal temperatures were ~5 ℃ (3-8 ℃) lower during the last glacial maximum, and ~2 ℃ (1-3 ℃) higher during the Holocene optimum; while the annual and seasonal precipitation have 30-150 % variations, with greater seasonality during the middle Holocene at 8-5 ka. A distinct paleoclimate variability was found in transitional zone between the humid monsoon and the dry desert areas. These results generally agree with paleoclimate reconstructions by other independent methods, including temperatures inferred from lacustrine branched glycerol dialkyl glycerol tetraethers (brGDGTs), monsoon intensities based on leaf-wax hydrogen isotopes, as well as monsoon precipitation and paleoenvironment condition derived from carbonate and dolomite contents, stable carbon isotopic composition and environmental magnetism analyses from loess deposits with high-resolution absolute optically stimulated luminescence dating constraints. These quantitative and semi-quantitative paleoclimate reconstructions from different parts of China also show a heterogeneous and notable diversity in regional temperature and precipitation variability, for both annual and seasonal signals. Based on the novel data assimilation method of optimal information extraction (OIE), we find that summer temperature and precipitation during the Current Warm Period in China are not unprecedented over the past ~21 ka, in particular in the monsoonal China, and that changes in summer temperature and precipitation are mainly driven by boreal summer insolation. We do find a conspicuous regional diversity in paleoclimate variations during the past ~21 ka, regarding amplitude, frequency and forcing mechanism.

AS07-A009 | Invited
EASM-EAWM Relation From Decadal to Orbital Scales

Mi YAN#+
Nanjing Normal University, China

East Asian monsoon has two important components, East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM). Studies have found that EASM and EAWM are correlated and have interactions. The relationship between EASM and EAWM at different timescales reveals the corresponding controlling factors of regional climate variabilities in East Asia. At interannual scale, there is a biennial oscillation between the EASM and EAWM variation. A strong EAWM might be followed by a strong EASM, and then a weak winter monsoon which leads to a weak summer monsoon, and a strong winter monsoon, thus forms a quasi-biennial cycle. Such relationship illustrates the basic air-sea-land interactions. At scales from decadal to millennial, the EASM and EAWM are anti-correlated, mainly attributed to the internal variabilities, including e.g., PDO, AMO and AMOC at corresponding scales. These internal variabilities, which we call annual forcings, have prolonged influence from summer to winter climate. At orbital scales, the EASM and EAWM are positively correlated according to the enhanced/weakened seasonality induced by changes of precession and obliquity. The forcings introducing enhanced/weakened seasonality are defined as seasonal forcings. It is worth noting that the topography of icesheet can modify the EASM-EAWM variations at orbital scales, which change from in-phase to out-of-phase after large-scale development of major NH glaciation. We can conclude that EASM and EAWM are anti-correlated when the climate is dominated by annual forcings whereas positively correlated when the climate is dominated by seasonal forcings.

Characteristics and Mechanisms of Multi-scale EASM Weakening Events During the Holocene

Liang NING1,2#+, Jian LIU1, Zhengyu LIU3, Mi YAN1, Sun WEIYI1, Raymond BRADLEY2, Kefan CHEN1, Yanmin QIN1
1Nanjing Normal University, China, 2University of Massachusetts, United States, 3The Ohio State University, United States

The eastern Asian summer monsoon (EASM) showed obvious multi-scale variability with extreme weakening events during the Holocene, which are of great interests to the broad fields of climatology, geology, and geography.  Besides the recent abundant Holocene paleoclimate archives at relatively high temporal and spatial resolutions, there are also great improvements of the modeling on EASM weakening events during the Holocene. The spatio-temporal characteristics and mechanisms of the multi-scale EASM weakening events, e.g., 4.2ka BP event and decadal megadroughts, have been investigated through two groups of climate modeling (i.e., NNU-Holocene and NNU-2ka) and comparisons between reconstruction and simulations. The results show that, on millennial scale, proxy reconstructions and model simulations revealed significant increases of NHLMP due to the green Sahara during mid-Holocene. on centennial scale, one potential mechanism behind the 4.2ka BP event is the multi-century-scale fluctuations in SSTs across the North Atlantic and AMOC strength, superimposed on the steady decline in SSTs and AMOC led by long-term changes of orbital forcing. On decadal scale, the frequency of EASM weakening events is larger in LIA than MCA, because the EASM weakening are more sensitive to weak PDO phases during LIA. There is also a linear relationship between the SSI intensities and precipitation differences over eastern China between positive PDO and negative PDO phases, which is related to the changes of monsoon circulation and SLP gradient with the SSI intensities. Moreover, the aridification during recent decades over northern China associate with EASM weakening is triggered by phase shifts of PDO and AMO, which could be induced by anthropogenic forcings.

Synchronicity of East Asia and Global Temperature Changes Over the Last Millennium

YaWen LIU+, Mi YAN#
Nanjing Normal University, China

In this study, the data of the last millennium (850~2005) ensemble simulation experiment (CESM-LME) from the Community Earth System Model (CESM) were employed to analyze the synchronization of temperature changes between East Asia and the world over the past millennium on a centennial scale. CESM can provide a reasonable simulation of temperature variation in East Asia. The results from 7 climatic experiments have been analyzed, including all forcing experiment (AF), total solar irradiation experiment (TSI), volcanic eruption experiment (VOL), greenhouse gas experiment (GHG), land use and land cover change experiment (LUCC), orbital elements experiment (ORB), and ozone and aerosols experiment(Oz./Aer.). Moreover, the external reasons for the synchronous change of temperature in East Asia and the world were preliminarily discussed. The results indicate that the temperature change in East Asia during the Medieval Warm Period(MWP) and Little Ice Age(LIA) in the last millennium were approximately consistent with the whole world on the centennial scale, but some differences exist in some centuries. TSI, ORB, and VOL forcings are the main factors for the differences in temperature change between East Asia and the whole world, and some other external forces show a small impact. In the Current Warm Period(CWP), especially in the late 20th century, the temperature changes in East Asia and the world show great asynchrony. The temperature increase in East Asia is less intense than that in the world. Anthropogenic external forcing plays a controlling role in this period. Amplification in climate warming caused by greenhouse gas concentration is found to be obvious in the Earth’s poles, implying the main external reason for the differences in temperature change between East Asia and the world. Meanwhile, Oz./Aer. forcing also causes some impacts.

Mon-01 Aug | 13:00 - 14:30 | MR02
AS03 - The Asian Monsoon: Past, Present and the Future

Session Chair(s): Renguang WU, Zhejiang University

AS03-A024 | Invited
The Indian Summer Monsoon Under Future Warming in CMIP6 Models: Seasonal Rainfall, Variability and Extremes

1Potsdam Institute of Climate Impact Research, Germany, 2University of Potsdam, Germany, 3Ludwig Maximilian University Munich, Germany

The Indian summer monsoon plays a crucial role in India’s agriculture and shapes many other aspects of life affecting the livelihood of a fifth of the world’s population. It is therefore highly relevant to assess its change under potential future climate change. Here, we use 32 of the climate models within the Coupled Model Intercomparison Project Phase 6 (CMIP6) in order to analyze the model projections for the 21st century with particular focus on the seasonal summer monsoon rainfall, its interannual variability and the occurrence of extremes. All of the models show a substantial increase in June-to-September (JJAS) mean monsoon rainfall under unabated climate change (SSP5-8.5) and most do also for the other three Shared Socioeconomic Pathways analyzed (SSP1-2.6, SSP2-4.5, SSP3-7.0). Moreover, the simulation ensemble indicates a linear dependence of rainfall on global mean temperature with a high agreement between the models independent of the SSP. Most models project that the increase will contribute to the precipitation especially in the Himalaya region and to the northeast of the Bay of Bengal, as well as the west coast of India. Interannual variability is found to be increasing in the higher-warming scenarios by almost all models. Under the shared socioeconomic pathway SSP5-8.5, very wet monsoon seasons as observed in 1 out of 10 years in 1900-1950 are projected to occur in 8 out of 10 years in 2050-2100 on multi-model average. With only 6 out of 10 seasons found to be very wet in 2050-2100 under the SSP2-4.5 scenario, we show that even modest efforts to mitigate climate change can have a strong impact on the frequency of very strong rainfall seasons. The CMIP6 simulations largely confirm the findings from CMIP5 models, but show an increased robustness across models with reduced uncertainties and updated magnitudes towards a stronger increase in monsoon rainfall.

AS03-A004 | Invited
The Role of Tropical Volcanic Eruptions in Exacerbating Indian Droughts

Suvarna FADNAVIS1#+, Rolf MÜLLER2
1Indian Institute of Tropical Meteorology, India, 2Forschungszentrum Juelich, Germany

The Indian summer monsoon rainfall (ISMR) is vital for the livelihood of millions of people in the Indian region; droughts caused by monsoon failures often resulted in famines. Large volcanic eruptions have been linked with reductions in ISMR, but the responsible mechanisms remain unclear. Here, using 145-year (1871 – 2016) records of volcanic eruptions and ISMR, we show that ISMR deficits prevail for two years after moderate and large (VEI > 3) tropical volcanic eruptions; this is not the case for extra-tropical eruptions. Moreover, tropical volcanic eruptions strengthen El Niño and weaken La Niña conditions, further enhancing Indian droughts. Using climate-model simulations of the 2011 Nabro volcanic eruption, we show that eruption induced an El Niño like warming in the central Pacific for two consecutive years due to Kelvin wave dissipation triggered by the eruption. This El Niño like warming in the central Pacific led to a precipitation reduction in the Indian region. In addition, solar dimming caused by the volcanic plume in 2011 reduced Indian rainfall.

AS03-A017 | Invited
Aerosol Variations Over India by the Monsoon Intra-seasonal Oscillation

1Tokyo Metropolitan University, Japan, 2Japan Agency for Marine-Earth Science and Technology, Japan

The spatial and temporal modulation of aerosol species by the monsoon intraseasonal oscillation (MISO) were investigated using the Copernicus Atmosphere Monitoring Service reanalysis data and Moderate Resolution Imaging Spectroradiometer satellite (MODIS) observations from 2003 to 2020. The climatological spatial distribution of aerosol species showed that dust aerosols are dominant over the Arabian Peninsula, East African Himalayan foothills. The predominant aerosols in the Himalayan foothills were organic matter, black carbon, and sulfate. During the MISO, anomalous southwesterly or westerly flow variability was found to be responsible for the transport and spatial distribution of these species. During MISO phases 2 to 5 (the active phase of the Indian summer monsoon), strong southwest monsoon winds transported sea-salt aerosols from the Arabian Sea to the Indian region. In phases 5 to 7, which are associated with the transition from the active to the break phase of the Indian monsoon, dust transport from the Arabian Peninsula and East Africa strengthened. The total aerosols over the Indian subcontinent peaked in phases 6 and 7. Anomalous cyclonic circulation during MISO phases 2–4 over central India controlled the westward movement of organic matter, sulfate, and black carbon along the Himalayan foothills. These dynamic spatial changes in aerosols due to the MISO over the Indian region affected the shortwave and longwave radiation balances, and thus can alter the monsoon circulation.

Unraveling the Changes in Indian Summer Monsoon: A Global Climate Model Perspective

Amita KUMARI+, Pankaj KUMAR#
Indian Institute of Science Education and Research Bhopal, India

The Indian Summer Monsoon (ISM) plays an intrinsic role in the global climate system. It is the backbone of India’s economy as it supports the livelihood of the world's one-fifth population. ISM is considered as a giant hydrological cycle associated with several complexities and variabilities of a wide spectrum. Therefore, future changes in ISM are highly relevant for regional socioeconomic assessments. This study highlights the changes in ISM using a suite of the Global Climate Models (CMIP6) by the end of the century. The study also examines the major drivers in controlling these changes, such as mean sea level pressure, low-level jet, and low-level moisture transport. In this regard, the performance of 15 GCMs were analyzed beforehand to get reliability into the future projection, i.e. mid (2041-2070) and far (2071-2100) future under unabated climate change (Share Socioeconomic Pathways; SSP585), respectively. CESM2-WACCM, MIROC6, MPI-ESM1-2HR and NorESM2-MM were found to be the best GCMs that have the ability to capture the mean rainfall over India. All models except CESM2-WACCM shows a substantial increase in mean rainfall over most of the Indian landmass in the mid and far future. The projected strong low-level jet along with enhanced low-level moisture transport towards the region leads to enhanced rainfall over the region. Since ISM plays a vital role in modulating the global climate, it is imperative to analyze the projected changes that can help in better planning and strategies to mitigate the incurred losses.

Examination of the Relation Between Climate and Precipitation-δ18O Over Eastern Asia

Nitesh SINHA#+, Axel TIMMERMANN, Sun-Seon LEE
Pusan National University, Korea, South

The interpretation of East Asian monsoon speleothem δ18O records is heavily debated in the paleoclimate community. Besides developing new speleothem proxies, the use of isotope-enabled climate simulations is one of the key tools to enhance our understanding of speleothem δ18O records. Here we present results from novel climate simulations performed with the fully coupled isotope-enabled Community Earth System Model (iCESM1.2), which simulates global variations in water isotopes in the atmosphere, land, ocean, and sea ice. The model closely captures the major observed features of the isotopic compositions in precipitation over East Asia for the present-day conditions. To better understand the physical mechanisms causing interannual to orbital timescale variations in δ18O in East Asian speleothems, we ran a series of experiments with iCESM. We perturbed solar, orbital, bathymetry, ice-sheet. The simulations supporting of observations/reconstructed records from East Asia, help understand the controls on the isotope composition of East Asian monsoon rainfall and how speleothem δ18O records may be interpreted in terms of climate. The study provides new insights into the mechanisms of East Asian monsoon changes on different timescales.

Investigating the Atlantic-Indian Summer Monsoon Multidecadal Teleconnections in the PMIP3 Last Millennial Simulations

Arijeet DUTTA1#+, Rahul SIVANKUTTY2, Neena Joseph MANI3
1Indian Institute of Science Education and Research, India, 2British Antarctic Survey, United Kingdom, 3Indian Institute of Science Education and Research, Pune, India

Understanding the natural variability of Indian summer monsoon (ISM) is a crucial aspect relevant for decadal climate predictions and climate change studies. The multidecadal variability of ISM is known to have a close association with the Atlantic multidecadal oscillations (AMO). Several teleconnection pathways have been suggested to explain the co-variability of the AMO and ISM in multidecadal timescales. One hypothesis is that the AMO modulates the interannual North Atlantic Oscillation (NAO) mode and there by influences the monsoon via Eurasian temperature modulations. Another possibility is the AMO modulating the monsoon via the Pacific pathway through the atmospheric bridge mechanism and associated modulations of the Hadley-Walker circulations. The Last millennial (850-1850) climate simulations part of the PMIP3 gives an opportunity to better understand the fidelity of climate models in capturing the AMO-ISM teleconnection mechanisms. In this study we explore how well the proposed mechanisms are represented in eight global climate models (GCM) LM simulations. Such a study, assessing the validity of different AMO-monsoon teleconnection mechanisms in different model climates provides crucial information about how reliable the respective GCMs may be in making decadal climate predictions.

Mon-01 Aug | 15:00 - 16:30 | MR01
AS30 - Climate Changes and Land-air Interactions in Cold Regions

Session Chair(s): Xianhong MENG, Cold and Arid Regions Environmental and Engneering Institute,Chinese Academy of Sciences

Genesis of Tibetan Plateau Vortex: Roles of Surface Diabatic and Atmospheric Condensational Latent Heating

Feimin ZHANG#+, Chenghai WANG
Lanzhou University, China

Numerical simulations of a nighttime-generated Tibetan Plateau Vortex (TPV) are conducted using the advanced Weather Research and Forecasting (WRF) model. It is found that the nighttime TPV forms as a result of the merging of convections. Although the WRF model can reproduce the genesis of the nighttime TPV well, colder and drier biases in the lower atmosphere and drier biases in the upper atmosphere are still presented, thus degrading the simulation performance. Inter-comparisons among the experiments indicate that the simulations are more sensitive to land surface schemes than to cloud microphysics schemes. The development of convection is more favorable when daytime surface diabatic heating is vigorous. Surface diabatic heating during daytime plays a dominant role in the development of daytime convection and the genesis of nighttime TPV. Further diagnosis of the PV budget reveals that the obvious increase in PV in the lower atmosphere is associated with the evidently strengthened cyclonic vorticity during TPV genesis. This could be attributed to the increased vertical component of net across-boundary PV fluxes during the merging of convections, as well as the significant positive contribution of diabatic heating effects in the lower atmosphere. Therefore, strong daytime surface diabatic heating, which is essential to convection development, could provide a favorable condition for nighttime TPV genesis. Overall results illuminate the complicated process of TPV genesis. 

Comparative Analysis of Water-energy Cycle Processes Based on a High-resolution Assimilation Dataset of the Water-energy Cycle Over Different Underlying Surfaces in Qinghai-Tibet Plateau

Xiaohang WEN1#+, Siqiong LUO2
1Chengdu University of Information Technology, China, 2Chinese Academy of Sciences, China

We used a High-Resolution Assimilation Dataset of the water-energy cycle in China (HRADC) to study the land-atmosphere interactions and meteorological characteristics in inhomogeneous underlying surface of the Qinghai-Tibet Plateau (QTP). Three different underlying surfaces (i.e., grassland, open shrubland, and barren or sparsely vegetated) of the QTP are selected and the meteorological elements on each underlying surface grid are averaged. We compared and analyzed the Green Vegetation Fraction (GVF), precipitation, soil moisture and soil temperature, and energy fluxes for three different land-use types in QTP. The results showed that the vegetation coverage of HRADC showed a gradual decrease trend from southeast to northwest throughout the Qinghai-Tibet Plateau. The GVF of the grassland in the southeast can reach more than 60% in summer, and only about 20% in sparse vegetation areas. HRADC can well reproduce the seasonal change trend of soil temperature and soil moisture in different underlying surfaces. The annual variation trend of soil temperature shows that the time of the deep soil temperature reaching the peak value lags behind the shallow layer. The annual averaged soil moisture over grassland is higher than that of open shrubland and barren land, which is consistent with the plateau precipitation distribution. The peak value of sensible heat flux over grassland is only 80 W·m-2 in April, and the latent heat flux can reach 90 W·m-2, and the net radiation of the barren land can reach 210 W·m-2 in July. This study is important to discover the water-energy cycle characteristics of QTP.

Simulation of the Dipole Pattern of Summer Precipitation Over the Tibetan Plateau by CMIP6 Models

Wei SHANG1#+, Keqin DUAN1, Xuejuan REN2, Bo HUANG3
1Shaanxi Normal University, China, 2Nanjing University, China, 3Norwegian University of Science and Technology, Norway

The dipole pattern of summer precipitation over the Tibetan Plateau (TP) during 1961–2014 is evaluated based on observations and 18 models provided by the Coupled Model Intercomparison Project Phase 6. Of the 18 models, 10 can capture the opposite variation characteristics in the south and north TP. Observational data reveals that the south–north seasaw of TP summer precipitation is essentially driven by a Rossby wave propagating from the Western Europe to East Asia, which is associated with North Atlantic oscillation (NAO). The models successfully simulated the dipole pattern that is closely related to the reproduction of the NAO–TP relationship. Further analysis demonstrates that the reliable simulations of horizontal dynamic processes of moisture transport, which is linked to the NAO–TP relationship, highly contributes to their success in reproducing the dipolar pattern of TP summer precipitation. While unrealistic local vertical circulation and evaporation simulation lead to the failed reproductions. These findings provide significant information for model development and future climate change projections.

Impact of Transient Eddy Fluxes on the Dust Storm Event: Cases Study in South Xinjiang, China

Yan LI#+
Lanzhou University, China

Although the frequency and intensity of dust storm event (DSE) have decreased in northern China in recent years, its occurrence and impacts continue, with a more complex formation mechanism under climate change background. Focusing on 7 spring DSEs occurred during 1980-2018 in South Xinjiang, China, this study tries to explain the formation of abnormal atmospheric circulation during the DSE from the perspective of transient eddy fluxes by using the physical decomposition method. The results suggest that 2 days prior to the outbreak of the DSE (“Day -2”), the convergence of transient-momentum transport is beneficial for increasing wind speed to become a jet stream (JS) in the upper level above South Xinjiang. Then, until “Day 0”, wind speed in the mid-high troposphere remains as a JS, with the largest value on “Day -1”. Through downward upper-level momentum, the lower-level wind increases to a maximum value on “Day 0”. Additionally, the direct influence of transient-heat transport convergence and the indirect influence of transient-momentum transport divergence are helpful for the establishment of the Ural ridge under the negative phase of Eurasian (EU) teleconnection pattern, reinforcing the Siberian Highs (SH) and leading to low-level gales. Consistent high winds at the low-high levels and obvious vertical motion (descending from “Day -3” to “Day -1” and ascending from “Day 0” to “Day +2”) result in dust emissions and transport. Thus, the dust column mass density (CMD) begins to concentrate in South Xinjiang on “Day -2” and achieves the strongest on “Day 0”. Although the influence of the transient eddy and the wind speed decrease after the DSE outbreak, atmospheric circulation is also helpful for dust to expand to adjust and downstream regions over the following 4 days.

Mon-01 Aug | 15:00 - 16:30 | MR07
AS18 - Carbon Neutrality, Clean Air and Regional Interactions

Session Chair(s): Jingxu WANG, Ocean University of China, Yingying YAN, China University of Geosciences

AS18-A016 | Invited
Mass-conserving and Measurement Constrained Method for Quantifying Emissions and Impacts of Short-lived Climate Forcers

Jason COHEN#+
China University of Mining and Technology, China

This work introduces a new framework for identifying the spatial and temporal distribution and magnitude of short-lived climate forcers, and their impacts on air pollution and climate. The approach uses remotely sensed measurements at daily time step and resolutions ranging from kms to tens of kms in connection with a simple mass-conserving first order model of physics and chemistry to quantitatively estimate emissions, in-situ processing, and transport. The approach is self-consistent and has been applied successfully to a few such species. In this work, results from BC, Ozone and Methane will be highlighted. Three important scientific findings include: day-to-day emissions estimates of both means and a robust error quantification, allowing analysis of both source attribution and natural sink potential; overall underestimations of emissions of these species lead to an overevaluation of climate costs associated with CO2 and air pollution costs associated with PM2.5; differentiated severe underestimation in some geographic areas at all times and in other geographic areas certain times of the years, coupled with moderate overestimation in some areas all times of the year and other areas during certain times of the years allows for a more nuanced approach to attribution and mitigation. Specific examples demonstrated include vast improvements from coal-fired power plants and steel producing regions, and hidden emissions associated with large-scale biomass plantations. Overall, the idea of simple scaling of existing emissions inventories is shown to not be sufficient to attribution and emissions magnitude quantification, requiring further new collaboration opportunities with both the emissions and mitigation communities. 

Numerical Study of the Regional Transport of PM2.5 Over the North China Plain Under Two Typical Wintertime Synoptic Patterns

Weihang ZHANG#+, Lifang SHENG, Yuanhong ZHAO, Yang ZHOU , Wencai WANG, Shangfei HAI
Ocean University of China, China

Regional transport is one of the major causes of severe haze pollution in the North China Plain (NCP), whereas little is known about its detailed process and its influencing mechanisms. In our study, two regional transport episodes under the two typical synoptic patterns, eastern high-pressure system and cold frontal passage, are investigated by using the WRF-Chem model. Under the eastern high-pressure system, regional transport of pollutants from the south-central area of the NCP could contribute up to 70% of the PM2.5 concentration to the northern NCP (Beijing-Tianjin-Hebei region). Simultaneously, the pollutants derived from regional transport were located mainly at an altitude of 0.5–1.5 km during the accumulating stage and at 0–3 km during the severely polluted stage, which caused mainly by the height of the inversion layer and the strength of the wind. When cold fronts swept over the NCP region, pollutants led by the regional transport could be lifted to ~3 km along the frontal surface and influence downstream areas. PM2.5 concentrations near-surface increased temporarily at up to 15 μg·m−3·h−1 behind the surface frontal line, owing to the inversion layer triggered by the oblique frontal surface. Cold fronts may also indirectly exacerbate near-surface pollutant diffusion conditions by affecting solar radiation incidence, with a reduction of the 2-m temperature by as much as 1°C, increasing near-surface PM2.5 concentrations by up to 40 μg·m−3. This study emphasizes that the inter-regional cooperation would be essential in improving air quality in the NCP region.

The Combined Effect of Two Westerly Jet Waveguides and Its Corresponding Rainfall-induced Diabatic Heating on Haze in the North China Plain in Winter

Xiadong AN1+, Lifang SHENG1#, Wen CHEN2, Chun LI1, Yang GAO1, Jianping LI1, Qian LIU3, Yulian TANG2, Jingliang HUANGFU2
1Ocean University of China, China, 2Chinese Academy of Sciences, China, 3Sun Yat-sen University, China

Severe haze occurred in the North China Plain (NCP) from November to December 2015, with a wide spatial range and long duration. In this paper, the combined effect of the anomalous stationary Rossby waves within two westerly jet waveguides on this haze event is investigated based on observational visibility data and NCEP/NCAR reanalysis data. The results show that circulation anomalies in Eurasia caused by the propagation of anomalous stationary Rossby wave energy along two waveguides within the westerly jet originating from the Mediterranean were responsible for haze formation in the NCP. The Rossby waves propagated eastward along the subtropical westerly jet and the polar front jet, causing an anomalous anticyclone over the Sea of Japan and anticyclonic wind shear at 850 hPa over the NCP, which enhanced the anomalous descent in the middle and lower troposphere and subsequently resulted in a stable state of the lower atmosphere. Furthermore, the anomalous stationary Rossby waves propagating along the polar front jet weakened the East Asia trough and Ural ridge and strengthened the anomalous southerly wind at 850 hPa over the coastal areas of eastern China, decelerating the East Asia winter monsoon. The above meteorological conditions modulated haze accumulation in November and December 2015. Meanwhile, continuous rainfall related to ascending motion due to Rossby wave propagation along the waveguide provided by the subtropical westerly jet occurred in southern China. The associated latent heat release acted as a heat source, intensifying the ascending motion over southern China so that the descending motion over the NCP was strengthened, favoring the maintenance of severe haze. This study elucidates the formation and maintenance mechanism of widespread haze in the NCP in late fall and boreal winter.

Source Apportionment of PM2.5 Using PMF Combined Online Bulk and Single-particle Measurements: Contributions of Biomass Burning and Fireworks During the Chinese New Year in Hong Kong

Yanjing ZHANG1+, Wenshuai LI1, Yang ZHOU 1#, Lei LI2, Mei LI2, Zhen ZHOU2, Jianzhen YU3
1Ocean University of China, China, 2Jinan University, China, 3Hong Kong University of Science and Technology, China

Online measurements with high time resolution are beneficial to study the atmospheric process of transient pollution events. This study combined the online bulk and single-particle measurements to investigate the biomass burning and firework transition process during the Chinese New Year in Hong Kong from 8th to 14th Feb 2013. Single particle aerosol mass spectrometer (SPAMS), a monitor for aerosols in ambient air (MARGA), and sunset OCEC instruments were concurrently deployed to obtain the single-particle and bulk aerosol information. We conducted positive matrix factorization (PMF) to resolve the pollution sources using two different input schemes. Four sources were identified, including Biomass Burning + Fireworks, Secondary Aerosols, Vehicles + Road Dust, and Sea Salt when the input data only contains bulk measurements data. While the PMF result with combined bulk and single-particle datasets can extract the fireworks from the biomass burning and an industry source was additionally obtained. Combustion source (fireworks and biomass burning) is the primary source of particulate matter during the sampling period in this study. We identified two fireworks discharge processes in this study. EP1 (from midnight on the 9th to 10:00 on the 11th) was mainly contributed by fresh fireworks, and EP2 (from 21:00 on the 11th to 00:00 on the 13th) was contributed primarily by aged fireworks. Overall, the combination of online bulk and single-particle measurement data provides a new perspective for applying source apportionment of aerosols using PMF.

Towards Reducing Inter-provincial and Inter-city Economic Inequality Embedded in China's Environmental Protection Tax Law

Jingxu WANG1+, Jintai LIN2#, Kuishuang FENG3, Klaus HUBACEK4
1Ocean University of China, China, 2Peking University, China, 3University of Maryland, United States, 4University of Groningen, Netherlands

In response to the severe environmental problems, China implemented the Environmental Protection Tax Law in early 2018. Although the tax is levied based on producers, the taxation burden can be transferred to consumers through products’ increasing price. Based on the MRIO model and the official calculation method of environmental tax, our study quantifies the taxation induced by household consumption and the tax intensity of residents from both provincial and city-based perspectives. The national tax revenue due to household consumption is estimated to be 32 billion Yuan in 2012, only one seventh of the related economic loss from premature mortality. Due to China’s regional imbalanced economic development and pollution transfer caused by inter-regional trade, our study reveals that tax intensities in different regions are unmatched with their affluence levels under current environmental tax, which aggravates regional inequalities. We further analyze some scenarios of alternative levy mechanisms. If each province or city imposes taxes to products it consumes (rather than produces, as in the current mechanism), with the tax rate linearly dependent on its per capita consumption expenditure, this would effectively reduce inter-provincial and inter-city inequality. Moreover, if tax revenues could be used to support emission control, such as installing suites of ULE technology in the power and industrial sectors nationally, regional economic inequality would be further alleviated while improving the environment and reducing tax payers’ economic burden.

Mon-01 Aug | 15:00 - 16:30 | MR03
AS07 - Asian Paleo-monsoon: Reconstructions and Simulations

Session Chair(s): Liang NING, Nanjing Normal University, Qin WEN, Nanjing Normal University

Local Insolation Drives Afro-Asian Monsoon at Orbital-scale in Holocene

Qin WEN#+
Nanjing Normal University, China

Insolation changes play an important role in driving monsoon changes at orbital time scales. One key issue that has remained outstanding is whether the Asian monsoon is driven by local insolation from the Northern Hemisphere (NH) or remote insolation from the Southern Hemisphere (SH) at orbital band. Here, we perform a set of sensitivity experiments to quantify the impacts of local and remote insolation changes on the Afro-Asian summer monsoon at 11ka B.P relative to the present. We show that the Afro-Asian summer monsoon is overwhelmingly driven by the precession induced local insolation change in the tropical-subtropical NH. The insolation from NH high latitudes also affects the Afro-Asian summer monsoon. In contrast, the insolation from SH plays a negligible role. Our model experiments support the idea that the Afro-Asian summer monsoons are driven predominantly by the direct forcing of NH low latitudes summer insolation for the Holocene.

Characteristics and Attributions of Centennial Summer Extreme High Temperature Events in Asia During the Holocene

Lu LIU#+
Nanjing Normal University, China

With the expansion of the impact of extreme climate on the economy, environment and human life, extreme climate has received increasing attention in current climate change research. Based on the Holocene (NNU_Holocene) temperature data and atmospheric circulation data from Nanjing Normal University, the spatiotemporal characteristics and attributions of the extreme high temperatures in summer in Asia are analyzed, and the physical mechanism of the spatiotemporal characteristics is further discussed. The results of the characteristics of temporal and spatial variation show that the extreme high temperature in Asia in summer during the Holocene has consistent spatial characteristics and 600-year periodic oscillations. The attribution results show that volcanic forcing has a significant impact on the temporal and spatial characteristics of the extreme high temperature in Asian summer during the Holocene. Analyses of these physical mechanisms show the high pressure of the Asian summer geopotential height field and the sinking motion of the vertical velocity field are conducive to the increase of temperature. At the same time, we found that the decrease in water vapor transport caused by the weakening of the Asian summer monsoon will cause a decrease in cloud cover and an increase in the downward solar radiation flux, thus leading to an increase in temperature. In addition, we found that the 600-year cyclical oscillation of the extreme summer heat in Asia is related to the 600-year cyclical oscillation of AMO.

Holocene Multi-centennial Variations of the Asian Summer Monsoon Driven by Solar Activity

Weiyi SUN1#+, Jian LIU1, Bin WANG2, Deliang CHEN3
1Nanjing Normal University, China, 2University of Hawaii, United States, 3University of Gothenburg, Sweden

Solar activity has been suggested to affect Asian summer monsoon (ASM) at various time scales. However, it remains unknown if and how solar activity can influence ASM on a multi-centennial time scale. Using a solar-forced Holocene transient simulation with the Community Earth System Model (CESM), we show that during the middle‒late Holocene ASM precipitation exhibits a significant 300‒600-year periodicity under solar forcing. This model-produced multi-centennial variation is also suggested by high-resolution proxy data. The leading mode of the multi-centennial ASM variation shows a “wet tropics–dry subtropics” pattern, which lags the corresponding solar activity by about a quarter cycle. We find that the key circulation system responsible for the multi-centennial ASM variation is an anomalous western North Pacific (WNP) cyclone, which enhances the climatological south Asia‒WNP monsoon trough. We suggest that solar activity modulates the zonal SST gradients of the tropical Pacific, inducing the anomalous WNP cyclone and enhancing ASM precipitation in a delayed mode. These findings have implications for predicting the influence of the anticipated future solar activity on the Asian monsoon system.

Mon-01 Aug | 15:00 - 16:30 | MR02
AS03 - The Asian Monsoon: Past, Present and the Future

Session Chair(s): Kyung-Ja HA, Pusan National University

Spatial Synchronization Patterns of Extreme Rainfall Events in the Asian Summer Monsoon Region

Shraddha GUPTA1#+, Zhen SU1, Niklas BOERS2, Jürgen KURTHS1, Norbert MARWAN1, Florian PAPPENBERGER3
1Potsdam Institute for Climate Impact Research, Germany, 2Technical University of Munich, Germany, 3European Centre for Medium-Range Weather Forecasts, United Kingdom

A deeper knowledge about the spatially coherent patterns of extreme rainfall events in the South and East Asian regions is of utmost importance for substantially improving the forecasts of extreme rainfall as their agro-based economies predominantly rely on the monsoon. In our work, we use a combination of a nonlinear synchronization measure and complex networks to investigate the spatial characteristics of extreme rainfall synchronicity in the Asian Summer Monsoon (ASM) region and gain a comprehensive understanding of the intricate relationship between its Indian and East Asian counterparts. We identify two modes of synchronization between the Indian Summer Monsoon (ISM) and the East Asian Summer Monsoon (EASM) – a southern mode between the Arabian Sea and south-eastern China in June which relates the onset of monsoon in the two locations, and a northern mode between the core ISM zone and northern China which occurs in July. Thereafter, we determine the specific times of high extreme rainfall synchronization, and identify the distinctively different large-scale atmospheric circulation, convection and moisture transport patterns associated with each mode. Furthermore, we discover that the intraseasonal variability of the ISM-EASM interconnection may be influenced by the different modes of the tropical intraseasonal oscillation (ISO). Our findings show that certain phases of the Madden-Julian oscillation and the boreal summer ISO favour the synchronization of extreme rainfall events in the June-July-August season between ISM and EASM. This work is funded by the CAFE project which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 813844.

Quantification of Physical Factors of EAWM Surface Circulation Formation

Hae-Li PARK#+, Kyong-Hwan SEO
Pusan National University, Korea, South

The East Asian Winter Monsoon (EAWM) is the strongest in its intensity among global winter monsoon system. Many studies have recognized the thermal and mechanical forcing of Tibetan Plateau (TP) can be one on the most important forcing for that. However, quantification of physical mechanism generating climatological circulation pattern of the EAWM has not been fully understood. In this study, based on the general circulation model simulations, the relative contributions of thermal and mechanical effect of orography, and land-sea thermal contrast in generating the zonal asymmetric sea level pressure pattern of EAWM are examined. The experiment with idealized Eurasian continent (EU), TP, Mongolian Plateau (MP) and North American continent and Rocky Mountain provides a decent simulation of the sea level pressure pattern. Sensitivity experiments are designed by applying and withdrawing factors of the possible total forcings. As a results, Land-sea thermal contrast explain most (responsible for ~70%) of the Siberian High (SH) intensity and its center location, with mechanical effect of orographic forcings (accounts for ~29%) playing a secondary role, and thermal effect of orographic forcing (~1%) play only minor role. On the other hand, mechanical effect of orographic forcings (~47%) play major role on the Aleutian Low (AL) intensity and its center location, land-sea thermal contrast (~18%) do not have high influence as for SH, and thermal effect of orographic forcing (~1%) playing minor role as SH. Results of this study suggest that EU with TP and MP is important in forming SH and AL coincide with its climatological intensity and center location. It appears that the mechanical effect (mountain drag effect, mountain uplift effect, and mountain horizontal deflection effect) of TP and MP located in the EU can be the reason why the EAWM is strongest among global winter monsoon system.

Addressing Abrupt Global Warming, Warming Trend Slowdown and Related Indian Summer Monsoon Features in Recent Decades

Indrani ROY#+
University College London, United Kingdom

The puzzle of recent global warming trend slowdown has captured enough attention, though the underlying cause is still unexplained. This study addresses that area segregating the role of natural factors (the sun and volcano) to that from CO2 led linear anthropogenic contributions. It separates out a period 1976–1996 that covers two full solar cycles, where two explosive volcanos erupted during active phases of strong solar cycles. The similar period also matched the duration of abrupt global warming. It identifies that dominance of Central Pacific (CP) ENSO and associated water vapor feedback during that period play an important role. The possible mechanism could be initiated via a preferential alignment of NAO phase, generated by explosive volcanos. Inciting extratropical Rossby wave to influence the Aleutian Low, it has a modulating effect on CP ENSO. Disruption of Indian Summer Monsoon and ENSO during the abrupt warming period and a subsequent recovery thereafter can be explained from that angle. Interestingly, CMIP5 model ensemble, and also individual models, fails to comply with such observation. It also explores possible areas where models miss important contributions due to natural drivers.

A Climatological Study on Precipitation Microphysical Characteristics Over Asian Monsoon Region Using GPM/DPR

Moeka YAMAJI1#+, Hiroshi TAKAHASHI2
1Japan Aerospace Exploration Agency, Japan, 2Tokyo Metropolitan University, Japan

Precipitation is one of the most essential parameters in the Earth system. Especially, the Asian monsoon brings abundant precipitation to densely inhabited regions, and can be a significant water resource for daily human activities. The seasonal precipitation variations over the Asian monsoon region can be the most characteristic worldwide. Not only variations in the amount of precipitation but also changes in precipitation characteristics can be of great concern in terms of intensifying floods and droughts under climate change. This study focuses on the microphysical properties of precipitation which has not yet been addressed in terms of statistical aspects and aims to investigate the climatological characteristics of precipitation microphysical structures over the Asian monsoon region by using eight years of Dual-frequency Precipitation Radar abord Global Precipitation Measurement Mission Core Observatory (GPM/DPR). Precipitation rate, mass-weighted mean diameter (Dm), precipitation top height, frequency of heavy ice precipitation etc. were statistically analyzed in this study. It was confirmed that eight years of accumulated precipitation dataset by GPM/DPR can be used to detect differences in precipitation characteristics between pre-monsoon and monsoon seasons. We found that Dm was larger, and the land-ocean contrast was clearer in the pre-monsoon than in the monsoon season. The region and season with large Dm were consistent with the regions where deep convective core was dominant as explained in previous studies. The results were consistent with that precipitation top height was higher in the region and season with large Dm. It is known that precipitation amount is less but there are more active lightning and deep convections in pre-monsoon season. We investigated frequency of the existence of heavy ice precipitation by GPM/DPR. The results showed that frequency of heavy ice precipitation was larger over land in pre-monsoon season, which can be related to the results of large Dm. 

Impact of the South China Sea Summer Monsoon on the Indian Ocean Dipole in CMIP5 Models

Yazhou ZHANG+, Jianping LI#
Ocean University of China, China

The impact of the South China Sea summer monsoon (SCSSM) on the Indian Ocean dipole (IOD) has been systematically investigated in observations. This study focuses on the ability of climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) to reproduce the observed relationship between the SCSSM and IOD, and the relevant physical mechanisms. All 23 models reproduce significant correlations between the SCSSM and IOD during boreal summer (June–July–August, JJA), whereas the influence of the SCSSM on the IOD varies considerably across the CMIP5 models. To explore the causes, all models are divided into two groups. Models that successfully simulated both the correlations between the SCSSM and JJA IOD and of the SCSSM and JJA IOD with precipitation over the western North Pacific and Maritime Continent are classified as Type-I, and these produce stronger low-level wind anomalies over the tropical southeastern Indian Ocean. The stronger low-level wind anomalies enhance local sea surface temperature (SST) anomalies via positive wind–evaporation–SST (WES) and wind–thermocline–SST (Bjerknes) feedbacks. This corresponds to a strengthening of IOD events due to the increased zonal gradient of SST anomalies over the tropical Indian Ocean. In contrast, Type-II models perform poorly in representing the relationship between the SCSSM and JJA IOD or relevant atmospheric bridges, corresponding to weaker WES and Bjerknes feedbacks, and produce weaker IOD events. These results demonstrate that the better the model simulation of the atmospheric bridge, the larger contribution of the SCSSM to the IOD.

Tele-connections Among South and East Asian Monsoons

Ramesh KRIPALANI1,2#+, Preethi BHASKAR1, Milind MUJUMDAR1, Amita PRABHU1, Kyung-Ja HA3, Jai-Ho OH4, Renguang WU5
1Indian Institute of Tropical Meteorology, India, 2Pukyong and Pusan National Universities, Korea, South, 3Pusan National University, Korea, South, 4Nano C&W, Korea, South, 5Zhejiang University, China

Trends and tele-connections in the summer monsoon rainfall over South and East Asia are examined. Trend analysis indicates that over South Asia one contiguous region over northern part India exhibits a significant decreasing trend and another region over the southern part of India exhibits a significant increasing trend during summer (June through September). However over East Asia two regions one over the Korea-Japan peninsula and another over South China indicate a significant increasing trend. These trends are evident post 1970s. Outputs from the Coupled Model Inter-comparison Project are investigated using historical simulations and future projections. In spite of large spread among the models, future projections in the summer monsoon rainfall over South as well as East Asia indicate a multi-decadal variability, displaying certain epochs of more rainfall over South Asia than over East Asia and vice versa. Tele-connections between the South and East Asian monsoon rainfall also exhibits a multi-decadal variability with alternate epochs of strengthening and weakening relationship. Thus, in general an out-of-phase relation between these two large monsoon systems is indicated, however the recent Monsoon 2020 witnessed heavy rains over South Asia and devastating heavy rains over East Asia. Possible reasons for such an in-phase relation during Monsoon 2020 will be suggested.

Mon-01 Aug | 17:00 - 18:30 | MR03
AS07 - Asian Paleo-monsoon: Reconstructions and Simulations

Session Chair(s): Weiyi SUN, Nanjing Normal University, Qin WEN, Nanjing Normal University

Understanding Global Monsoon Precipitation Changes During the 8.2 ka Event and the Current Warm Period

Peng HE1,2+, Jian LIU2#, Bin WANG3, Sun WEIYI2
1Beijing Meteorological Bureau, China, 2Nanjing Normal University, China, 3University of Hawaii, United States

Global monsoon (GM) precipitation has profound impacts on water resources, food security, and the livelihood of about two-thirds of the world's population. Understanding the contrasting changes of GM precipitation (GMP) during the 8.2 ka cold event and the present-day warm event helps better comprehend the common origin of the GMP change and its future projection. We analyzed a suite of transient climate evolutions (TraCE-21 ka simulation). We show that the simulated monsoon rainfall changes during the 8.2 ka abrupt cooling event are qualitatively consistent with the paleoclimate archive collected worldwide. The simulated Northern Hemisphere monsoon (NHM) precipitation significantly decreased by 12.4% per one degree of global mean temperature change (12.4%/°C) while the Southern Hemisphere monsoon (SHM) precipitation increased by 4.2%/°C. The cooling-induced suppressed upward motion plays a dominant role in reducing NHM precipitation, and the reduced moisture adds to the circulation effect, whereas the enhanced SHM precipitation is mainly due to the moisture increase. In the 8.2 ka event, the circulation response reinforces the moisture-induced drought over the NHM region, resulting in an excessive precipitation sensitivity to temperature change (12.4%/°C). In contrast, during the present warm period, the greenhouse warming-induced moisture and circulation effects cancel each other, resulting in a moderate sensitivity (1.8%/°C). Although meltwater and greenhouse gas forcings induce contrasting global temperature change patterns, the GMP changes are governed by common root causes: forced NH-SH thermal contrast, land-ocean thermal contrast, and the tropical SST gradients. The moisture change plays a crucial role in altering precipitation amount but not spatial distribution. We suggest that the external forcing-induced warming (cooling) pattern drives the circulation changes (dynamic effects), determining the spatial structure of the monsoon rainfall change in the past, present, and future.

Effects of Consecutive Volcanic Eruptions on AMOC Over Past Millennium and Their Contributions to the LIA

Kefan CHEN1#+, Liang NING1, Zhengyu LIU2, Jian LIU1, Mi YAN1
1Nanjing Normal University, China, 2The Ohio State University, United States

AMOC is one of the most important poleward heat conveyor belt in the ocean, which has profound impacts on regional climate as well as marine ecosystems. Volcanic eruption, as one of the strongest external forcings, have different impacts on AMOC at different time scales. Previous studies pointed out that the cooling of LIA is associated with weakening of AMOC on centennial time scale, which may be caused by successive volcanic eruptions. However, the timing of the onset and termination of LIA is still under debate. What is the attribution of consecutive volcanic eruption on LIA? Does the volcanic eruption play a role in triggering, maintaining or terminating LIA through AMOC? And what are the mechanisms behind the phase transition of AMOC at decadal and centennial timescales is still unclear.     In this work, based on simulations of CESM-LME as well as an energy balanced model, we explored the impacts of 4 consecutive volcanic eruptions in the past millennium on AMOC at different time scales, and studied their contributions to the onset, maintaining and ending of the LIA. The mechanisms behind the phase transitions of AMOC at different time scales after volcanism are also investigated. Our findings show that the 4 successive volcanic eruptions enhanced AMOC firstly on decadal time scales, and then weakened it centennially. The durations of positive and negative AMOC phases induced by volcanism overwhelm that originating from internal variability. We also found out that the four consecutive volcanic eruptions led to a stepped decline of temperature during the LIA through the long time weakening of the AMOC. This also explained the onset and maintaining of the LIA. Finally, the recovery of AMOC at the end of the LIA is related to the increases of Green House Gases, which plays a pivotal role in the ending of the LIA.

Decadal Precipitation Projections Over Eastern China Constrained by the Interdecadal Pacific Oscillation

Yanmin QIN1+, Liang NING1,2#, Longhui LI1, Zhengyu LIU3, Jian LIU1, Mi YAN1, Kefan CHEN1
1Nanjing Normal University, China, 2University of Massachusetts, United States, 3The Ohio State University, United States

A reliable projection of future decadal precipitation is crucial for large population and social development in eastern China. However, large uncertainties (e.g., model bias, and internal variability) in now available model simulations cause unreliable future projection of decadal precipitation. Using a 90-member ensemble of simulations from Community Earth System Model Large Ensemble Project (CESM2-LE), we find that internal variability contributes most of decadal precipitation variability with 70% to 80% contribution of uncertainties, leads to large uncertainties in future projection of simulations. We further confirm that the interdecadal Pacific oscillation (IPO) can constrain the 30% to 40% internal variability of uncertainties effectively in projections. The length and magnitude of a future megadrought over the eastern China can be accurate estimated by fixing a certain IPO phase. Our results demonstrate that the uncertainties in projections of the decadal precipitation over eastern China can be reduced by improving prediction of IPO and other internal modes of climate variability.

Decadal Variability of Land Monsoon Precipitation Over Northern Hemisphere Over the Past Millennium

Tianyin SHEN#+, Jian LIU, Weiyi SUN
Nanjing Normal University, China

Understanding the decadal variability of land monsoon rainfall in the northern hemisphere (NHLMR) over the past millennium is crucial to the global water cycle and economic development of monsoon countries. However, due to the limitation of time and space scale of observation and reconstruction data, previous studies on the decadal variability of NHLMR over the past millennium are relatively few. In this paper, based on the Community Earth System Model (CESM) climate simulation experiment for the past millennium and the validation of the CCSM4 and FGOALS-s2 experiment and reconstruction data of Paleoclimate Modelling Intercomparison Project Phase III(PMIP3), the characteristics and mechanism of the decadal variability of NHLMR in the past millennium are investigated. The results show that the extended El Niño–Southern Oscillation (XEN) sea surface temperature (SST) index has remained stable in the past millennium, which is mainly controlled by the internal variability of the climate system. The North Atlantic–south Indian Ocean dipole (NAID) sea surface temperature (SST) index shows an unstable state, with an obvious trend of fluctuation near 1212 and 1740. By comparing the single factor sensitivity experiments, it is found that the NAID index in the volcanic experiment shows the same characteristics around 1212 and 1740, which is consistent with the volcanic reconstruction records. Therefore, it is believed that the volcano is an important factor causing the change of NAID and controlling the decadal variation of NHLMR.

Tue-02 Aug | 08:00 - 09:30 | MR01
AS08 - Future of Cities within the Context of Climate Change

Session Chair(s): Fei CHEN, National Center for Atmospheric Research

AS08-A001 | Invited
The Impact of Increasing Greenhouse Gas Concentration and Urban Expansion on Extreme Precipitation Across US Cities

1Arizona State University, United States, 2National Institute of Water and Atmospheric Research, New Zealand, 3University of Guelph, Canada

Projections of future regional-scale extreme precipitation require assessments accounting for the interacting effect of greenhouse-gas (GHG) induced climate change and urban development. In this work, I discuss decadal scale numerical modelling results conducted with the Weather Research and Forecasting (WRF) model that include the twin forcing agents of urban climate change - impacts arising from increasing concentration of GHGs and effects arising from continued urban expansion - on continental US (CONUS) cities. The results presented highlight, in agreement with prior work, that urban areas can exacerbate or diminish extreme precipitation across CONUS cities. However, when accounting for the twin forcing agents of urban climate change, results indicate a systematic shift toward increased extreme precipitation that is correspondingly greater as the thresholds of extreme precipitation become greater. The robustness of the presented results is examined by noting the similarity in simulated extreme precipitation from WRF dynamical downscaling of a pair of distinct GCMs. I conclude with a community call-to-action of next steps that are required to more appropriately characterize future extreme precipitation across global urban watersheds using a coordinated and systematically designed set of convection-resolving simulations. Such systematically designed experiments are necessary to better inform the ever-important dialogue on adapting to a future climate that is both warmer and flashier.

Impact of Urban Roughness Representation on Regional Hydrometeorology Simulation

Jiachuan YANG1#+, Qi LI2, Long YANG3
1The Hong Kong University of Science and Technology, Hong Kong SAR, 2Cornell University, United States, 3Nanjing University, China

Previous studies have shown that the widely-used Weather Research and Forecasting model (WRF) tend to overestimate near-surface wind speeds in urban areas. Recently, studies have established high-resolution urban canopy parameter (UCP) database and incorporated it with WRF to improve the simulation accuracy. In this study, we conducted high-resolution urban climate simulations to evaluate the impact of implementing UCP with the latest versions of the single-layer (UCM) and multi-layer (BEP) urban canopy models. Results show that UCP has a limited impact on the simulation accuracy of urban air temperature. In terms of wind speed simulation, UCP can significantly reduce the error of the BEP model, especially on windy days in winter. The wind speed simulation accuracy of UCM decreases after adding UCP. We found a systematic error in both urban canopy models: the simulation accuracy of urban wind speeds is significantly positively correlated with the impervious surface ratio and the building surface ratio. This suggests that existing models have poor performance in low-density urban areas, and an improved aerodynamic parameterization scheme is needed to better utilize UCP. Based on this finding, we explored how to improve the aerodynamic parameterization scheme in UCM by combining large eddy simulation (LES) and WRF. Results show that the UCM model will underestimate the frontal area index when using 3D UCP data, leading to an underestimation of urban surface roughness and a further overestimation of near-surface wind speed. Replacing the drag parameterization scheme in UCM with LES-based aerodynamic parameters has a significant impact on near-surface wind speed simulations, especially during rainfall. Our study uncovers some of the limitations of current urban weather simulations and provides guidance for future model development.

Urbanization Effects on Rainfall Processes Induced by Landfalling Typhoon Lekima (2019) Over the Shanghai Metropolitan Area

Xiangyu AO1#+, Caijun YUE2, Xuchao YANG3, Lin DENG1, Wei HUANG1
1China Meteorological Administration, China, 2Shanghai Marine Meteorological Center, China, 3Zhejiang University, China

Urbanization effects on rainfall induced by landfalling tropical cyclones have rarely been studied. Here high-resolution numerical simulations with the Weather Research and Forecasting/Noah/Single-layer urban canopy model system (WRF/SLUCM) are conducted to investigate impacts of urban land cover and building heights on heavy rainfall induced by landfalling Typhoon Lekima (2019) over the Megacity Shanghai. The default single urban category in WRF was updated to a new land cover data with three urban categories. Results indicate that WRF/SLUCM captures the typhoon intensity, track and total rainfall amount quite well. Urbanization has a small positive effect on rainfall amount for this event. However, urbanization has a significant impact on the spatial distribution of the accumulated rainfall with enhancement not confined over the urban area but mainly to the southwest of Shanghai possibly due to the changes of the typhoon tracks. With the impact of typhoon Lekima, the urban heat island disappears, indicating that the thermal effect of urbanization has limited influence on the rainfall processes. The model performance is very sensitive to the building height. More realistic building height values can noticeably improve simulations of the diurnal patterns of rainfall, urban heat island and the urban wind speed stilling effect. With the rising of building heights, the surface frictional dynamic effect and vertical uplift is enhanced, but seems not enough to intensify the rainfall. The simulated lower level large moisture flux convergence corresponds well to rainfall peaks. This study has important scientific significance for the accuracy of rainfall forecast of landfalling typhoons and disaster mitigation of cities.

On the Influences of Urbanization on the Extreme Rainfall Over Zhengzhou on 20 July 2021: A Convection-permitting Ensemble Modeling Study

Yali LUO1#+, Jiahua ZHANG2, Miao YU1, Xudong LIANG1, Rudi XIA1, Yanyu GAO1, Xiaoyu GAO1, Jinfang YIN1
1Chinese Academy of Meteorological Sciences, China, 2Chengdu University of Information Technology, China

This study investigates the influences of urban land cover on the extreme rainfall event over the Zhengzhou city in central China on 20 July 2021 using the Weather Research and Forecasting Model at a convection-permitting scale (1-km resolution in the innermost domain (d3)). Two ensembles of simulation (CTRL, NURB), each consisting of 11 members with a multi-layer urban canopy model and various combinations of physics schemes, were conducted using different land cover settings: (i) the “real” urban land cover, (ii) all cities in d3 being replaced with natural land cover. The results suggest that CTRL reasonably reproduces the spatiotemporal evolution of rainstorms and the 24-h rainfall accumulation over the key region, although the maximum hourly rainfall is underestimated and displaced to the west or southwest by most members. The ensemble mean 24-h rainfall accumulation over the key region of heavy rainfall is reduced by 13%, and the maximum hourly rainfall simulated by each member is reduced by 15–70 mm in CTRL relative to NURB. The reduction in the simulated rainfall by urbanization is closely associated with numerous cities/towns to the south, southeast and east of Zhengzhou. Their heating effects jointly lead to formation of anomalous upward motions in and above the planetary boundary layer (PBL), which exaggerates the PBL drying effect due to reduced surface moisture flux and also enhances the wind stilling effect due to increased surface friction. As a result, the lateral (from the south and east boundaries) inflow of moisture to Zhengzhou is reduced.

Assessing the Impacts of Urbanization on the Urban Hydro-climate Using High-resolution Coupling of Land Surface and Hydrological Models in WRF-Hydro

Ulysse PASQUIER#+, Pouya VAHMANI, Andrew JONES
Lawrence Berkeley National Laboratory, United States

Urban flooding is a rising source of economic loss and social disruption throughout the world and much of the United States. In California – where 95% of the population resides within urban areas – flood risk is growing and threatening key systems and infrastructure. At the same time, cities are facing water shortages due to increasing demand across sectors, severe drought and uncertainty in the future of water resources. The resilience of cities is further challenged by climatic changes and varying patterns of extreme weather events. In this context, the management of floods and droughts requires an advanced understanding of urban hydrology to implement appropriate adaptive strategies. Current modeling practices lack or under-represent dynamics of the land surface, hydrologic and atmospheric processes at a city or regional scale. In this study, the WRF-Hydro modeling system was adapted to represent urban imperviousness in a multi-scale, physics-based, approach. The modeling framework was used to analyze surface runoff and groundwater recharge during extreme precipitation events under different scenarios of urban development. The coupling of atmospheric, land surface and hydrological models within WRF-Hydro moreover provides insights into the local impacts of urbanization on the urban climate. While the focus of this study was the LA metropolitan area, the presented modular and reproducible approach offers opportunities for other sprawling cities of the world to better understand the impacts of urban development.

Uncertainties in Urban Climate Downscaling Associated with Future Urbanization

Quang-Van DOAN1#+, Hiroyuki KUSAKA1, Lidia VITANOVA2, Ronald ESTOQUE3, Thanh Hung NGUYEN1, Fei CHEN4
1University of Tsukuba, Japan, 2Nikken Sekkei Research Institute, Japan, 3National Institute for Environmental Studies, Japan, 4National Center for Atmospheric Research, United States

Understanding uncertainties in future dynamical downscaling (DDS) is essential to effectively developing climate-change adaptation and mitigation strategies. There are well-known DDS uncertainties associated with future greenhouse-gas emission scenarios and the fidelity of global and regional climate models. However, the impact of future urbanization scenarios, especially over fast-urbanizing regions, on the DDS simulations has not been investigated. This paper assesses this uncertainty using Hanoi (a rapidly-growing megacity in Southeast Asia) as a case study. Outputs from a global climate model with scenario RCP8.5 are used for DDS, forced by different urbanization scenarios: status-quo, master-plan, and objectively-derived. Results showed that the different levels of urbanization can produce significant discrepancy in projected temperature. In the case of Hanoi, this discrepancy could reach a maximum of 0.6 - 0.8 ˚C, which is comparable to the global warming signal in the 2050s under the higher greenhouse-gas emission scenario RCP 8.5. This underlines the daunting challenge in employing a single future urbanization scenario for DDS, especially for rapidly-growing cities, which may lead to unrealistic and even wrong projection of consequences of future warming effects in densely populated regions.

Tue-02 Aug | 08:00 - 09:30 | MR07
AS09 - Observations, Remote Sensing, and Modeling of Tropospheric Composition and Air Quality in Asia and the Transpacific Region

Session Chair(s): Richard ECKMAN, National Aeronautics and Space Administration, Jun WANG, The University of Iowa

AS09-A002 | Invited
The Salt Rain from the Disappearing Aral Sea: An Analysis of the 2018 Summertime Dust Outbreak in Central Asia

Xi XIN#+
Michigan Technological University, United States

In the evening of 26 May 2018, an extreme dust storm was triggered by storm-force winds from the dry exposed seabed of the former Aral Sea (Aralkum), and produced a fast-moving dust cloud sweeping across the Turan Lowland and reaching the northern borders of Iran and Afghanistan. The storm was considered the worst in recent decades and described as “salt rain from the sky'' due to the high salt content in the lofted dust. Geostationary satellite observations reveal widespread dust emissions from a number of ground sources, including the dried-up Aral Sea, as Central Asia experienced frequent cold intrusion and a dry anomaly during the early summer of 2018. Based on satellite observations, surface synoptic reports, upper-air soundings, and atmospheric reanalysis, this presentation will present a detailed analysis of the dust aerosol trajectory and distribution, source location and geomorphology, synoptic-scale forcing, and large-scale climate drivers associated with the 2018 summertime dust outbreak in Central Asia.

AS09-A037 | Invited
Measuring Aerosol Optical Depth From Aircraft During KORUS-AQ Reveals Higher Consistency Than Aerosol Size

Samuel LEBLANC1,2#+, Michal SEGAL-ROZENHAIMER1, Jens REDEMANN3, Connor FLYNN3, Roy JOHNSON2, Stephen DUNAGAN2, Robert DAHLGREN4, Myungje CHOI5, Arlindo DA SILVA5, Patricia CASTELLANOS5, Qian TAN1, Luke ZIEMBA6, K. Lee THORNHILL7,6, Meloë KACENELENBOGEN2, Jhoon KIM8
1Bay Area Environmental Research Institute, United States, 2NASA Ames Research Center, United States, 3University of Oklahoma, United States, 4University of Minnesota, United States, 5NASA Goddard Space Flight Center, United States, 6NASA Langley Research Center, United States, 7Science Systems & Applications, Inc., United States, 8Yonsei University, Korea, South

The airborne sunphotometer – 4STAR (Spectrometers for Sky-Scanning Sun Tracking Atmospheric Research) – measured the aerosol optical depth (AOD) spectra and trace gases from the NASA DC-8 during the KORUS-AQ (KORean-US Air Quality) experiment in May-June 2016. These measurements over Korea and the surrounding waters are obtained at high spatial and temporal resolution. We show the consistency over spatial scales of the AOD and the aerosol intensive properties, Angstrom exponent (AE) and fine mode fraction (FMF), observed by 4STAR, GOCI (Geostationary Ocean Color Imager Yonsei aerosol retrieval v2), MERRA-2 reanalysis (Modern-Era Retrospective Analysis for Research and Applications, v2), and from airborne in situ aerosol optical measurements by LARGE (NASA Langley Aerosol Research Group Experiment). The majority of AODs due to fine mode aerosol is observed at altitudes lower than 2 km and is dependent on the prevailing meteorological conditions. AE and FMF are found to be more spatially variable than AOD during all of KORUS-AQ, even when accounting for potential sampling biases. This may indicate that microphysical processes like aerosol particle formation, growth, and coagulation impact the dominant aerosol size at shorter scales than their combined effect on the aerosol optical depth by the aerosol emission, transport, and removal. Averaging between measurements and model, the distance at which the correlation to itself is reduced by 15% is 65 km for AOD, and 22.7 km for AE. While there are observational and model differences (MERRA-2 consistently shows high autocorrelation for longer distances, compared to GOCI, LARGE in situ, and 4STAR observations), the predominant factor influencing AOD and AE consistency is the meteorological period. The shortest AOD and AE consistency occur during extreme pollution period (25–31 May), and the longest consistency during the blocking (1–7 June) and stagnation (17–22 May) periods.

Estimation of Secondary PM2.5 in China and the United States Using a Multi-Tracer Approach

Haoran ZHANG#+, Nan LI, Tang KEQIN
Nanjing University of Information Science & Technology, China

PM2.5, generated via both direct emissions and secondary formations, can have varying environmental impacts due to different physical and chemical properties of its components. However, traditional methods to quantify different PM2.5 components are often based on online observations or lab analyses, which are generally high economic cost and labor-intensive. In this study, we develop a new method, named multi-tracer estimation algorithm (MTEA), to identify the primary and secondary components from routine observation of PM2.5. By comparing with the long-term and short-term measurements of aerosol chemical components in China, as well as aerosol composition network in the United States, MTEA is proved to be able to successfully capture the magnitude and variation of the primary PM2.5 (PPM) and secondary PM2.5 (SPM). Applying MTEA to China national air quality network, we find that 1) SPM accounts for 63.5% of PM2.5 in southern cities of China averaged for 2014-2018, while in the North the proportion drops to 57.1%, and at the same time the secondary proportion in regional background regions is ~19% higher than that in populous regions; 2) the summertime secondary PM2.5 proportion presents a slight but consistent increasing trend (from 58.5% to 59.2%) in most populous cities, mainly because of the recent increase in O3 pollution in China; 3) the secondary PM2.5 proportion in Beijing significantly increases by 34% during the COVID-19 lockdown, which might be the main reason of the observed unexpected PM pollution in this special period; and at least, 4) SPM and O3 show similar positive correlations in the BTH and YRD regions, but the correlations between total PM2.5 and O3 in these two regions are quite different as PPM levels determines. In general, MTEA is a promising tool for efficiently estimating PPM and SPM, and has huge potential for the future PM mitigation.

Impact of Lidar Data Assimilation on Planetary Boundary Layer Wind and PM2.5 Prediction in Taiwan

Fang-Yi CHENG#+, Shu-Chih YANG, Sheng-Hsiang WANG, Chia-Hua HSU, Lian-Jie WANG
National Central University, Taiwan

Advanced remote sensing techniques, such as lidar detection and ranging (lidar), can provide aerosol information with high temporal and vertical resolutions in the PBL. In this study, a lidar data assimilation system was developed based on the Weather Research and Forecasting-Local Ensemble Transform Kalman Filter (WRF-LETKF) framework coupled with the Community Multiscale Air Quality (CMAQ) model. The objective was to investigate the impact of lidar data assimilation on PBL prediction and the subsequent influence on PM2.5 prediction for a high-air-pollution event. The fine particulate matter (PM2.5) profiles retrieved from two micropulse lidar observations were assimilated in the WRF-LETKF system. Three numerical experiments, BASE (with a nudging strategy), CTRL (with an ensemble framework), and LDA (with assimilation of lidar-retrieved PM2.5 profiles), were conducted for a high-air-pollution episode. The BASE simulation overestimates the wind speed, which also leads to PM2.5 underestimation. The CTRL and LDA simulations are able to improve the wind fields and enhance the PM2.5 accumulation. With a strong error correlation between the lidar-retrieved PM2.5 concentration and the wind fields, the LDA simulation effectively corrects the wind flow from the surface to the PBL top, which further adjusts the PM2.5 transport processes.

Development of UI-WRF-Chem for MAIA Satellite Mission: Case Demonstration

Huanxin ZHANG1#+, Jun WANG1, Nathan JANECHEK1, Meng ZHOU1, Cui GE1, Lorena Castro GARCIA1, Tong SHA2, Yanyu WANG3, Sebastian VAL4, Yuan WANG5, James MCDUFFIE4, David DINER4
1The University of Iowa, United States, 2Nanjing University of Information Science & Technology, China, 3Fudan University, China, 4Jet Propulsion Laboratory, California Institute of Technology, United States, 5California Institute of Technology, United States

The Multi-Angle Imager for Aerosols (MAIA) satellite mission seeks to understand how different types of particulate matter (PM) pollution affect human health with a focus on a discrete set of globally distributed Primary Target Areas (PTAs) containing major metropolitan cities. The MAIA investigation will integrate satellite observations, chemical transport models, and ground observations to generate maps of surface total and speciated PM for the PTAs, which will be used for epidemiological health studies. For the chemical transport model, we have developed a unified inputs (initial and boundary condition) framework for WRF-Chem (UI-WRF-Chem). These developments include: (a) application of NASA GEOS-5 (both GEOS FP and MERRA-2) data to provide both meteorological and chemical initial and boundary conditions for performing WRF-Chem forecasts at fine spatial resolution, (b) a stand-alone emission preprocessor that ingests both global and regional anthropogenic emission inventories as well as fire emissions, (c) application of MODIS land cover data to update surface properties, (d) application of GLDAS and NLDAS data to constrain surface soil conditions, and (e) a new soil NO emission scheme based on the Berkeley Dalhousie Iowa Soil NO (BDISNP) parameterization.   We first present the development of UI-WRF-Chem. Then, we demonstrate case studies over MAIA PTAs to illustrate model improvements. First, a strong dust storm originated from Taklamakan and Gobi deserts impacted the Beijing PTA during March 26 – 28, 2018. Preliminary results show that the 4 km UI-WRF-Chem runs with MERRA-2 providing chemical boundary condition, capture more finely resolved spatial signals associated with surface PM2.5 concentrations compared with MERRA-2 simulations. The second case study focuses on the air quality over the Los Angeles PTA and rural area in California. Our results show that UI-WRF-Chem run with the BDISNP scheme shows better agreement with TROPOMI NO2 columns, than the default soil NOx emission scheme.

Tue-02 Aug | 08:00 - 09:30 | MR08
AS45 - Aviation Meteorology

Session Chair(s): Jung-Hoon KIM, Seoul National University

AS45-A002 | Invited
Does ENSO Affect Global Clear-Air Turbulence?

University of Reading, United Kingdom

The El Niño Southern Oscillation (ENSO) affects the global atmospheric circulation, including the mid-latitude jet streams. Vertical wind shear instabilities in the jet streams generate clear-air turbulence (CAT), which is a major hazard to flying aircraft. Therefore, ENSO has the potential to influence global CAT, both locally in the tropics and remotely in the extra-tropics via teleconnections. Anecdotal evidence supports such an association: there was a large increase in aircraft pilots reporting turbulence over the USA during the winter of 1997–98, coinciding with one of the strongest El Niño events on record. Here we use reanalysis data to investigate linkages between ENSO and global vertical wind shear (and hence CAT) in northern hemisphere winter. Global maps of the anomalous vertical wind shear at 250 hPa are produced from composites of the five strongest El Niño and La Niña events since 1979. These maps indicate that the shear is significantly modified throughout the ENSO cycle across large parts of the globe. The changes are quantified by regressing wind shear in various regions against sea-surface temperature anomalies in the Niño 3.4 region. In the USA and Mexico, for example, we find a sensitivity of around 0.5 m s−1 (100 hPa)1 °C1, such that the shear increases by around 50% from 4 m s1 (100 hPa)1 during a strong La Niña event to 6 m s1 (100 hPa)1 during a strong El Niño event. Significant ENSO–shear relationships are also found in South America, the North Atlantic Ocean, East Asia, South-East Asia, Australia, and Africa. We conclude that ENSO has the potential to influence CAT globally. ENSO’s predictability could be exploited to produce seasonal CAT forecasts globally several months ahead, which may have practical benefits for the aviation sector, not least because turbulence increases aircraft fuel consumption.

Analysis of Recent Trends of Clear-Air Turbulence (CAT) in Wintertime Over the Northern Hemisphere

Université de Toulouse, France

Airplanes spend about 1% of cruise time in Moderate-Or-Greater (MOG) CAT, which is defined as any turbulence occurring in the atmosphere away from a visible convective activity. Recent studies have shown that under climate change, jet streams could be strengthened, and MOG CAT frequency could significantly increase. Assessing future CAT changes is a relatively new research topic and there are a lot of open questions. In particular, there is a need to understand the CAT trends in the present climate using atmospheric reanalysis and climate models and the mechanisms at play. In this study, we characterize present climate CAT trends in the northern hemisphere. For this purpose, we rely on a set of CAT indices computed with different reanalysis datasets (among whom ERA5) and experiments performed by CMIP6 climate models. The analysis of the CAT indices over the last four decades shows that CAT is more frequent over the North Atlantic, the Pacific Northwest, the Himalayas and the Rocky Mountains. We find that the spatial distribution of CAT over the North Atlantic is strongly related to the variability of large-scale circulation patterns. In particular, the occurrence of CAT is clearly associated with the positive phase of the North Atlantic Oscillation (NAO+) and the Atlantic Ridge weather regimes. It would be interesting to extend this analysis over the North Pacific, where the jet stream is the strongest. A significant positive trend of CAT frequency is found using reanalysis in different regions of the northern hemisphere. The signal-to-noise ratio estimated from the climate models still remains very weak in the present climate except over Northeast Asia, but it could be significantly enhanced in response to the anthropogenic forcing.

Estimation of Eddy Dissipation Rate (EDR) Using Radiosonde Data and Comparison With In-situ Flight EDR

Han-Chang KO+, Hye-Yeong CHUN#
Yonsei University, Korea, South

One third power of the eddy dissipation rate (EDR), which is a primary aviation turbulence metric, is calculated based on the Thorpe method using high vertical-resolution radiosonde data (HVRRD) observed at 68 operational stations in USA for 6 years (2012–2017), and the spatiotemporal distributions of the HVRRD-derived EDR (HVRRD-EDR) are compared with those of in-situ flight EDR observed from commercial airlines. To compare two datasets in a reasonable way, comparisons are made in main flight routes and at z = 20–50 kft. In addition, considering the radiosonde is launched at 00 and 12 UTC, the in-situ flight EDR observed within ±1 hour centered at 00 and 12 UTC are used exclusively. The maximum value of HVRRD-EDR is about 0.3–0.4, which is smaller than that of in-situ flight EDR (0.6–0.8). However, both datasets show a similar seasonal variation with the largest total occurrences in JJA and the smallest total occurrences in DJF. The ratio of moderate-or-greater (MOG) intensity turbulence events to the total turbulence events shows similar characteristics between the two datasets: vertically decreasing distribution in DJF and “left angle bracket” shape in other seasons. The horizontal distributions of the MOG ratio of HVRRD-EDR show large values primarily in the Rocky Mountains, and this feature is generally consistent with that of in-situ flight EDR. Especially, the pattern correlation coefficient (r) for MOG ratio is significant at z = 20–30 kft in JJA and SON.

Estimating the Impact of Global Warming on Aircraft Takeoff Performance in China

Panxi DAI1#+, Wei YUAN2, Mengxiang XU2, Wei SONG2, Peng ZHANG3
1Zhejiang University, China, 2Aviation Meteorological Center, China, 3Hebei Airlines, China

Aviation operations are significantly affected by weather conditions, such as high temperature days. Under global warming, the rising temperature decreases the air density and thus, reduces the maximum takeoff weight of an aircraft. In this study, we investigate the impact of global warming on the aircraft takeoff performance in 53 airports in China by combining observational data and CMIP6 climate projections. There is a distinct geographic inhomogeneity of critical temperature, above which the takeoff weight decreases significantly with the increasing air temperature, mostly due to differences in airport elevations. By the end of the century, under the SSP5-8.5 scenario (with average warming of 5.2 in China), the daily maximum temperature for nearly all summer days in West China and for about half of summer days in East China exceeds critical temperature, indicating frequent weight restriction will be necessary. We further examine the reduction of carrying capacity due to climate change. By the end of the century under the SSP5-8.5 scenario, the summer total carrying capacity will be reduced by about 2.8% averaged over all 53 airports. The impacts on airports in West China are nearly four times greater than those in East China, due to the higher vulnerability and stronger warming in West China.

Multi-Index Consensus (MIC) En-route Turbulence Prediction for Asia-Pacific Region

Hong Kong Observatory, Hong Kong SAR

The Multi-Index Consensus (MIC) methodology leverages machine learning techniques to optimally combine a rescaled suite of conventional turbulence indices based on numerical weather prediction (NWP) model output to generate skilful forecasts of en-route aviation turbulence. This paper introduces the formulation and validation results of MIC as implemented on the Hong Kong Observatory’s (HKO) AAMC-WRF, a large-area 10-km prediction system spanning the Indo-Pacific region, as well as more recent comparison results against a new in-house implementation of the MIC on HKO’s experimental GPU-based MPAS configuration.

Development of Aviation Turbulence Forecast System for the Republic of Korea Air Force

Dan-Bi LEE1+, Jung-Hoon KIM1#, Eun-Jae JO2, Yo-Hwan CHOI2, Sang-Hwan PARK2, Hyeon-Sung KIM2, Jae-Ik SONG2, Ki-Nam KIM2, Shin-Woung BYUN2, Jae-Don HWANG2
1Seoul National University, Korea, South, 2Republic of Korea Air Force Weather Group, Korea, South

Atmospheric turbulence that affects aircraft operations is largely divided into four categories: Clear-Air Turbulence (CAT) due to various atmospheric instabilities near jet streams, mountain wave turbulence due to wave activities caused by airflow across mountainous regions, convectively induced turbulence, and low-level turbulence in the atmospheric boundary layer. In this study, we developed an integrated turbulence forecasting system considering various turbulence generation mechanisms based on the Korea Air Force-Weather and Research Forecasting (KAF-WRF) model currently in operation by the weather group of the Republic Of Korea Air Force (ROKAF), and verified against available aircraft observation data for one year (2019.01–2019.12). The KAF-WRF model has three nested grid domains centered on the Korean Peninsula, and their model horizontal grid spacings are 12, 4, and 1.3 km, respectively. In the KAF-WRF-based turbulence forecast system, a suite of individual turbulence diagnostics was calculated using the KAF-WRF model outputs, and the individual diagnostics converted to an Eddy Dissipation Rate, which is an objective intensity of turbulence in the atmosphere, were combined by the ensemble mean method with their performance-based weights. The optimal suite of individual diagnostics was composed of the top individual diagnostics for domain 1, which show the best performance for turbulence forecasting over East Asia when combined. The performance skills of the KAF-WRF-based 12-h turbulence forecast showed that the turbulence forecasts for domains 1 and 2 have a good performance with an area under the relative operating characteristic curve (AUC) of ~0.8 although the turbulence forecast for domain 3 relatively has a bad performance with an AUC value of ~0.76. The new system developed in this study was found to be superior to the currently operational system with a single diagnostic of turbulence index 2, which will eventually provide better turbulence guidance in the ROKAF. 

Tue-02 Aug | 08:00 - 09:30 | MR09
AS60 - Atmospheric Rivers: Toward Global Understanding and Applications

Session Chair(s): Elias MASSOUD, University of California, Berkeley, Agniv SENGUPTA, University of California, San Diego

Atmospheric River Reconnaissance – A Research and Operations Partnership

Anna WILSON1#+, Marty RALPH1, Vijay TALLAPRAGADA2, Chris DAVIS3, Luca DELLE MONACHE1, James DOYLE4, Florian PAPPENBERGER5, Carolyn REYNOLDS4, Aneesh SUBRAMANIAN6, David LAVERS5, Luca CENTURIONI1, Alison COBB1, Jason CORDEIRA7, Jennifer HAASE1, Chad HECHT1, Brian KAWZENUK1, Jonathan RUTZ2, Ryan TORN8, Xingren WU2, Minghua ZHENG1
1University of California San Diego, United States, 2National Oceanic and Atmospheric Administration, United States, 3National Center For Atmospheric Research, United States, 4U.S. Naval Research Laboratory, United States, 5European Centre for Medium-Range Weather Forecasts, United Kingdom, 6University of Colorado Boulder, United States, 7Plymouth State University, United States, 8University at Albany, State University of New York, United States

Atmospheric rivers (ARs), narrow corridors of intense water vapor transport, contribute to 30-50% of the annual precipitation over the western U.S. that can be both beneficial and destructive. Forecast errors in landfalling ARs and the associated precipitation are sensitive to initial condition errors in and around the ARs while offshore, where there are significant gaps in observations in the presence of clouds and precipitation. The increased societal demands for improved AR landfall forecast accuracy highlight the need to advance numerical modeling through improved observations. Atmospheric River Reconnaissance (AR Recon) is an interagency, international collaborative project to collect unique observations in the northeast Pacific to improve AR landfall forecasts and associated weather during the winter. These observations are now officially called for in the U.S. National Winter Season Operations Plan. Global modeling centers (e.g., U.S. National Centers for Environmental Prediction, U.S. Navy, European Centre for Medium-Range Weather Forecasts) that assimilate these data in real-time have developed a Research and Operations Partnership (RAOP) under the leadership of Scripps Institution of Oceanography’s Center for Western Weather and Water Extremes to assess impacts and improve forecast skill. Beginning in 2019, the group partnered with the Scripps Lagrangian Drifter Laboratory-based NOAA funded Global Drifter Program to explore the potential of drifting ocean buoys with surface pressure sensors, in concert with dropsondes and data assimilation efforts, to support the project’s forecast improvement objectives. In addition, data streams making use of airborne radio occultation, an innovative technique making use of both GPS and satellites, were made available in near real-time beginning in 2022. This presentation will cover the accomplishments of the AR Recon RAOP, including a summary of targeting methods and data collection, plans for the coming years, and results to date of impact assessments and science advances made possible by these important observations.

Distinct Characteristics of Windy ARs and Wet ARs

Yang ZHOU1#+, Travis O'BRIEN2, William COLLINS1, Christine SHIELDS3
1Lawrence Berkeley National Laboratory, United States, 2Indiana University Bloomington, United States, 3National Center for Atmospheric Research, United States

Atmospheric rivers (ARs) are intensive poleward moisture transport events that are essential to the global hydrological cycle and regional water resources, and are often linked to extreme weather events. We categorize the winter northern Pacific ARs into wind-dominated (windy) and moisture-dominated (wet) ARs based on the first Principal Component on a combined matrix of 850 hPa wind and integrated moisture. With a similar distribution of integrated vapor transport (IVT), windy ARs have distinct characteristics compared with wet ARs. More windy ARs occur in the midlatitude, while wet ARs are more active in the subtropics. Results show that windy ARs are more associated with surface lows, where the strong pressure gradient can support the strong wind within ARs. Due to the rich moisture content, wet ARs are more likely to cause heavy precipitation. We show that ARs are related to about 50-70% of winter precipitation over the west coast of North America, and both windy and wet ARs contribute about 50%. By categorizing the landfalling ARs into different scales, we show that wet ARs dominate the high-category ARs (Category 4 and 5), and windy ARs have higher contributions in the lower categories. In connection to climate variability, both types ARs are affected by the El Nino Southern Oscillation. Windy ARs are significantly modulated by ENSO teleconnections, however, wet ARs are impacted by the local SST change. The behaviors of windy and wet ARs are also compared in CESM2 Large Ensemble simulations (LE). The CESM2-LE reproduces AR activity but with a northward shift of spatial distribution. Future work will investigate how windy and wet ARs change in the context of climate change.

Two Flavors of Atmospheric Rivers in the North Pacific

Chanil PARK#+, Seok-Woo SON
Seoul National University, Korea, South

Atmospheric rivers (ARs) are often considered to be transient and concurrent with extratropical cyclones. However, such a definition is not necessarily true for all ARs. In this study, we show that the ARs in the North Pacific have two different flavors. By decomposing the integrated water vapor transport (IVTA) into the high- and low-frequency components, it is shown that the high-frequency IVTA plays a dominant role in the cool-season ARs (transient flavor) in a good spatial agreement with the midlatitude storm track. In contrast, the low-frequency IVTA also becomes important in organizing the warm-season ARs (transient and quasi-stationary flavors), especially along the periphery of the North Pacific subtropical high. Such seasonal variation is particularly pronounced in the western half of the North Pacific and is not distinct in the North Atlantic. It turns out that while the transient flavor is governed by the midlatitude baroclinic disturbances in an analogy of canonical ARs, the quasi-stationary flavor is associated with a quasi-stationary pressure gradient induced by low-frequency eddies. The result suggests that not all ARs follow the same underlying dynamics. The two AR flavors may offer new insights into the diversity and seasonal/regional manifestation of ARs.

Climatology of Atmospheric Rivers and Associated Surface Warming in the Arctic

Chen ZHANG#+, Wen-Wen TUNG, Lei WANG, William CLEVELAND
Purdue University, United States

Atmospheric river (AR) is one conspicuous pathway for poleward transport of moisture from lower latitudes. It could interact with Arctic warming and sea ice decline. However, there has been a lack of comprehensive Arctic AR climatology. Thus, we created a detailed exploratory data analysis of the climatology of Arctic AR frequency of occurrence, trends, and the regional relationships with teleconnection patterns primarily with an ensemble of six 3-hourly integrated water vapor transport (IVT) or integrated water vapor derived AR indices from MERRA-2 and ERA5 between 1980 and 2019, respectively. Besides, NOAA outgoing longwave radiation, Hadley Centre sea surface temperature, NASA CERES SYN1deg surface radiation, passive-microwave sea ice concentration (SIC) from Nimbus-7 SMMR and DMSP SSM/I-SSMIS, as well as NOAA Climate Prediction Center teleconnection indices were used. The AR tracking and analysis were executed via distributed-parallel computing on a Hadoop cluster using the Divide & Recombine approach. The results showed that Arctic ARs detected by 12 MERRA-2 and ERA5-based indices have consistent climatology: Increased AR over the Arctic regions from the Pacific, across the Arctic, to the Atlantic side was observed in the recent 20 years, coinciding with sea ice retreat. Besides, ARs transported increasing moisture poleward to the Arctic. We also highlighted teleconnection patterns strongly modulate regional AR activities, with strongest signals in north Atlantic and Pacific sectors, which is consistent with AR spatial recurrence from K-Means clustering analysis with all 12 indices. Furthermore, synoptic circulations associated with teleconnection patterns, jet stream, and storm track modulated major AR events into the Arctic according to 95th-IVT-based indices. Accompanied with ARs, enhanced warming and moistening, increased downward longwave radiation, and associated SIC decline were observed. Particularly, Arctic Warming-North American Continent cooling occurred during negative Pacific-North American pattern. While during positive Arctic Oscillation, North America-Eurasian warming was observed simultaneously.

Tracking Atmospheric Rivers Globally: Algorithm Update, Parallel Implementation, and Application to ERA5

Bin GUAN1#+, Duane WALISER2
1University of California, Los Angeles, United States, 2Jet Propulsion Laboratory, California Institute of Technology, United States

Atmospheric rivers (ARs) are narrow, elongated, synoptic jets of water vapor that play important roles in the global water cycle and regional weather/hydrology. A number of different and largely complementary techniques have been developed in the community for the detection of ARs. Such techniques have facilitated the investigation of the basic characteristics of ARs, their influence on hydrological variability and extremes, and their representation in weather/climate models. However, most of the existing techniques only identify AR conditions at individual time steps, and do not track ARs across time and space as they propagate. The need for characterizing and understanding AR life cycles (i.e., from genesis to termination) and their variations between different regions motivated the development of an AR tracking algorithm suitable for global studies (Guan and Waliser 2019). The algorithm built on previous versions of the algorithm (Guan and Waliser 2015, with refinements in Guan et al. 2018) that identified AR shapes, i.e., AR conditions at individual time steps, using the 85th percentile of integrated water vapor transport (IVT) and other requirements on IVT direction, intensity, and geometry. In this presentation, we discuss further refinements to the algorithm since 2019, such as better filtering of tropical cyclones and fine-tuning of a few AR detection parameters, parallel implementation of the algorithm to facilitate application to high-resolution datasets, and examples from the application to the ERA5 reanalysis. Comparisons will be made with the previous version of the algorithm, and between ERA5 and other reanalysis products, to understand the sensitivity of the AR detection results. The presentation will also highlight the resources that will be made available to the community to facilitate analysis of ARs, including a global database of ARs based on multiple reanalysis products, the AR detection code, and codes for a suite of AR model evaluation metrics.

Extending the Atmospheric River Concept to Aerosols: Climatology, Major Transport Pathways, and Associated Air Quality Impacts

Sudip CHAKRABORTY1#+, Duane WALISER1, Bin GUAN2,1, Arlindo DA SILVA3
1Jet Propulsion Laboratory, California Institute of Technology, United States, 2University of California, Los Angeles, United States, 3NASA Goddard Space Flight Center, United States

Leveraging the concept of atmospheric rivers (ARs), a technique has been developed to detect the aerosol atmospheric rivers (AARs), i.e., long and narrow channels of enhanced aerosol transports, to understand the climatology and seasonality of the frequency, intensity, major transport pathways, and other characteristics of extreme aerosol transport events globally between 1997-2020. Aerosol transport data for five different species of aerosols – dust (DU), sea salt (SS), sulfate (SU), and carbonaceous (CA or BC, Black Carbon and OC, Organic Carbon) – are from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). AARs, unlike ARs, mostly transport aerosols in the zonal direction. On average, 30-40 AARs days per year can contribute 40-80% of the total annual aerosol transport at many locations along their major transport pathways. With this in mind, it is worth exploring to delineate the potential impacts of AARs on extreme air quality events. Using at least 15 years of data between 1997-2020 from Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) measurements, our analysis shows that more than 80% of the days with extremely poor air quality (AOD is >98th percentile of the analyzed years) are associated with AARs. DU (SU, OC, and BC) AARs are generally associated with days when coarse (fine) mode AOD is greater than the 98th percentile. Moreover, the highest-rank (within the local top 10; top 1 or 2 in many locations) extreme AOD days are also associated with AARs. Such extreme air quality events are noticed along the major transport pathways of AARs, such as the Caribbean region, Southern US, central Europe, China, India, Western US, South America, and South Africa. A reasonably good agreement is found regarding the AARs’ association with the extreme air quality events between MODIS, MERRA-2, and AERONET datasets.

Tue-02 Aug | 08:00 - 09:30 | MR04
AS21 - Ensemble Modeling of High-impact, Multi-scale Weather to Decadal Phenomena

Session Chair(s): Huiling YUAN, Nanjing University, Jie FENG, Fudan University, Malaquias PEÑA, University of Connecticut

AS21-A005 | Invited
Toward Unifying Short-term and Next-day Convection-allowing Ensemble Forecast Systems With a Continuously Cycling 3-km Ensemble Kalman Filter Over the Entire Conterminous United States

Craig SCHWARTZ1#+, Glen ROMINE1, David DOWELL2
1National Center for Atmospheric Research, United States, 2National Oceanic and Atmospheric Administration, United States

Using the Weather Research and Forecasting model, 80-member ensemble Kalman filter (EnKF) analyses with 3-km horizontal grid spacing were produced over the entire conterminous United States (CONUS) for 4 weeks using 1-h continuous cycling. For comparison, similarly-configured EnKF analyses with 15-km horizontal grid spacing were also produced. The EnKF analyses initialized 36-h, 3-km, 10-member ensemble forecasts that were verified with a focus on heavy precipitation. Additionally, forecasts were initialized from operational Global Ensemble Forecast System (GEFS) initial conditions (ICs) and experimental “blended” ICs produced by combining large scales from GEFS ICs with small scales from EnKF analyses using a low-pass filter. Precipitation forecasts initialized from 3-km EnKF analyses were more skillful and reliable than those initialized from downscaled GEFS and 15-km EnKF ICs through 12–18 and 6–12 h, respectively. Conversely, after 18 h, GEFS-initialized precipitation forecasts were better than EnKF-initialized precipitation forecasts. Blended 3-km ICs reflected the respective strengths of both GEFS and high-resolution EnKF ICs and yielded the best performance considering all times: blended 3-km ICs led to short-term forecasts with similar or better skill and reliability than those initialized from unblended 3-km EnKF analyses and ~18–36-h forecasts possessing comparable quality as GEFS-initialized forecasts. Collectively, these findings suggest blending high-resolution EnKF analyses with low-resolution global fields can potentially unify short-term and next-day convection-allowing ensemble forecast systems under a common framework.

Impacts of Sudden Stratospheric Warming on Extreme Cold Events in Early 2021: An Ensemble-based Sensitivity Analysis

Murong ZHANG1+, Xiao-Yi YANG1#, Yipeng HUANG2
1Xiamen University, China, 2Xiamen Meteorological Bureau, China

Sudden stratospheric warming (SSW) is an extraordinary event in winter polar stratosphere, characterized by a rapid rise of temperatures and consequent weakening of the stratospheric polar vortex (SPV), which can influence the surface temperature anomalies with a lead time of weeks and therefore becomes a promising predictor in subseasonal-to-seasonal (S2S) forecast of cold air outbreaks. Although the tropospheric impacts of SSWs were generally derived based on long-term reanalysis, detailed contribution of individual SSW event in extreme cold weather still awaits to be elucidated. The winter of early 2021 was strikingly impressive by extreme cold events over Asia and North America, which led to huge societal impacts such as the unprecedented power outages over central U.S. in mid-February 2021. Based on real-time S2S ensemble forecast, we investigated the influences of SSW on three successive extreme cold events (C1–C3) over Siberia, western Canada, and central U.S. The SSW was featured with successive displacement and split of the SPV. Ensemble-based sensitivity analyses showed that C1 and C2 were more related to SPV variations at a lead time of 1–2 weeks than C3. Within ensemble forecasts, a more elongated SPV with higher geopotential height over northern Eurasia were conducive to C1. By contrast, a SPV with the more poleward retreat from displacement contributed to C2. The forecast accuracy of stratospheric heights over the sensitive region at 2 weeks lead was significantly correlated with the forecast skill of the tropospheric circulation pattern preceding C1. These results promisingly suggest that the prediction of some surface cold events may be improved by a more accurate forecast of the key features in SPV variations. These features can be quantitatively revealed by ensemble statistics, and are worth further analyses and generalization based on more SSW events covered by S2S real-time ensemble forecast dataset.

Effects of Aerosols on the Ensemble Forecasting of Mei-yu Front Storms Over the Yangtze–huai River Valley

Lin LIU#+
China Meteorological Administration, China

The evolutions of two Mei-yu front storms under different humidity conditions were simulated in the Weather Research and Forecasting with Chemistry (WRF/Chem) model to investigate the effects of aerosols on the prediction of clouds and precipitation. Two groups of ensemble forecast experiments were carried out by turning the chemistry–aerosol module on and off. Comparison between the two groups of ensembles suggested that activating the chemistry–aerosol module improved the forecasting skill for precipitation exceeding 5 mm/h in the two storms. In contrast to the uniform cloud droplet number concentration (Nd) distribution adopted in the standard WRF model, the inhomogeneous Nd distribution in WRF/Chem agreed better with in-situ aircraft observations collected during two recent field campaigns. Scavenging in the two storms generally reduced the median Nd in the WRF/Chem ensembles, but increased the value in regions of heavy precipitation. The fewer and larger cloud particles in WRF/Chem promoted the conversion of cloud to rain and the accretion of cloud by rain, thereby leading to invigoration of low-level stratus clouds and precipitation. Enhanced warm-rain processes leave fewer cloud particles for further ascent and ultimately result in suppression of convective cloud and precipitation. Uncertainties still remain in the net effect of aerosols on convection and precipitation, largely due to the competing effects between cloud-core-based invigoration and cloud-periphery processes that appear to be modulated by environmental conditions such as humidity. These uncertainties, however, do not undermine the potential significance of incorporating chemistry–aerosol schemes in the operational forecasting of Mei-yu rainfall.

Correction of Monthly SST Forecasts in CFSv2 Using the Local Dynamical Analog Method

Zhaolu HOU+, Jianping LI#, Bin ZUO
Ocean University of China, China

Numerical seasonal forecasts in Earth science always contain forecast errors that cannot be eliminated by improving the ability of the numerical model. Therefore, correction of model forecast results is required. Analog-correction is an effective way to reduce model forecast errors, but the key question is how to locate analogs. In this paper, we updated the Local Dynamical Analog (LDA) algorithm to find analogs and depicted the process of model error correction as the LDA-correction scheme. The LDA-correction scheme was firstly applied to correct the operational seasonal forecasts of sea surface temperature (SST) over the period 1982–2018 from the state-of-the-art coupled climate model named NCEP Climate Forecast System version 2. The results demonstrated that the LDA-correction scheme improves forecast skill in many regions as measured by the correlation coefficient and Root Mean Square Error, especially over the extratropical eastern Pacific and tropical Pacific, where the model has high simulation ability. El Niño-Southern Oscillation (ENSO) as the focused physics process is also improved. The seasonal predictability barrier of ENSO is in remission and the forecast skill of Central Pacific ENSO also increases due to the LDA-correction method. The intensity of ENSO mature phases is improved. Meanwhile, the ensemble forecast results are corrected, which proves the positive influence from this LDA-correction scheme on the probability forecast of cold and warm events. Overall, the LDA-correction scheme, combining statistical and model dynamical information, is demonstrated to be readily integrable with other advanced operational models and has the capability to improve forecast results.

Tue-02 Aug | 08:00 - 09:30 | MR05
AS11 - The Science and Prediction of Tropical Cyclones

Session Chair(s): Chun-Chieh WU, National Taiwan University, Kosuke ITO, University of the Ryukyus

AS11-A001 | Invited
The Role of Radiative Interactions on Tropical Cyclone Development

Brian SODEN#+
University of Miami, United States

The impact of radiative interactions on tropical cyclone (TC) development and intensificaiton is investigated using a hierarchy of model simulations and observations. Model simulations indicate that the spatial gradient in radiative heating between the TC center and large-scale environment induces a secondary circulation that generates an upgradient transport of moist static energy towards the storm center. A coordinate set of model experiments under both realistic and idealized settings demonstrate the critical role of radiative heating on TC development, particularly at the earliest stages of formation. When radiative interactions are suppressed, TC frequency is reduced primarily due to a decrease in the number of pre-TC synoptic disturbances.  TC genesis is also delayed and shifts toward coastal regions, whereas TC lysis locations remain unchanged, reducing TC duration. Satelllite measurements provide further observational support of this mechanism, with the spatial gradient in radiative heating providing an important indicator of subsequent TC development and intensification. 

On the Potential Precursors for Rapidly-intensifying Tropical Cyclones in the Idealized Atmosphere-Ocean Coupled Environment

Jaedeok LEE1#+, Eun-Chul CHANG1, Chun-Chieh WU2, Kosuke ITO3, Ui-Yong BYUN1
1Kongju National University, Korea, South, 2National Taiwan University, Taiwan, 3University of the Ryukyus, Japan

The present study aims to investigate potential precursors of rapid intensification (RI) of the tropical cyclone (TC) in the idealized atmosphere-ocean coupled environment. In this idealized numerical simulation, environments such as vertical wind shear (VWS) and ocean eddy are imposed, respectively, on the basic states, with sea surface temperature (SST) of 27℃ and 30℃. The results show that TC tends to develop earlier about 48 h in the warmer ocean environment but its maximum intensification rate is smaller than in the lower SST environment. Furthermore, TCs developed in the lower SST environment is more likely to maintain a concentric eyewall. For VWS experiments, the convective activity inside the radius of maximum wind is further enhanced with 4 m s-1 VWS in the warmer ocean environment than in the lower SST environment. Meanwhile, TCs barely intensify with -8 m s-1 VWS. The ocean eddy experiments such as ±3℃ show that at the initial stage, TCs passing over the warm eddy can intensify earlier than the cold eddy experiment but in 27℃ SST, the TC intensification rate is smaller in the warm eddy experiment than in the cold eddy experiment. In particular, the storm passing over the cold eddy maintains the concentric eyewall structure well, which is similar to the lower SST experiment. In terms of TC size, TCs experiencing a warmer ocean environment can have a larger size. Lastly, all the experiments show that after the equivalent potential temperature anomaly is developed at 300 hPa, the tangential wind structure forms about 24 h later and then intensifies. We think that this result can help predict the timing of TC intensification, particularly for RI. In the main presentation, we will further discuss possible factors related to RI.

Numerical Prediction of Tropical Cyclogenesis: Identification of Large-scale Physical Processes Under the Monsoon Shear Line Synoptic Pattern

Mei LIANG1+, Johnny CHAN2#, Jianjun XU1, Munehiko YAMAGUCHI3
1Guangdong Ocean University, China, 2City University of Hong Kong, Hong Kong SAR, 3Japan Meteorological Agency, Japan

This is the second part of a two-part study to investigate the numerical prediction of tropical cyclogenesis. Part I presents a comprehensive statistical assessment of the performance of the high-resolution European Centre for Medium-Range Weather Forecasts deterministic forecasts in predicting tropical cyclone (TC) genesis over the western North Pacific between 2007 and 2018 using The International Grand Global Ensemble data. Among these forecasts, the ones that predict TC genesis occurring in the monsoon shear line synoptic pattern have the highest 5-day predicted skill. In this paper (Part II), the large-scale dynamic and thermodynamic variables associated with this type of genesis are examined to identify the physical processes likely responsible for TC genesis. Moist convection appears to be the first important factor. Deep convection in the initial time (Day -5) is concentrated near the inner core of the pre-genesis vortex. In the lower troposphere, the northeasterly flow to the north and southwesterly flow to the south of the pre-genesis vortex begin to strengthen at Day -4 and Day -3 respectively, and then the maximum wind centers move close to the genesis position (GP) from Day -3 to Day 0. Strong low-level radial wind and the associated absolute angular momentum (AAM) import develop from Day -4, which effectively force a transverse circulation and spin up a surface vortex near the GP. The vertical gradients of latent heat release and the decrease in mean-sea-level pressure from Day -3 further support the import of low-level AAM and the development of the low-level vortex. At the upper-levels, an anticyclone moves close to the GP, reducing the vertical wind shear at Day -2, fully establishing the secondary circulation system. The positive feedback between the environmental flow and the internal thermal forcing conditions from Day -2 to the genesis time are also important to genesis.

Simulation of Hurricane Florence with WRF Relating to Ocean Heat Response

Panpan LU1+, Clair STARK1#, Elizabeth A. RITCHIE2, Scott TYO2
1University of New South Wales Canberra, Australia, 2Monash University, Australia

Tropical cyclones (TCs) are one of the most devastating natural weather disasters globally. Through their strong surface winds, TCs also change the ocean heat content, which may regulate climate change by impacting global energy transport. Reanalysis data and uncoupled models are typically used to study the impact of TCs on ocean heat content. However, these often underestimate the more intense TC winds which contribute more to TC induced ocean heat uptake (OHU) than weaker systems. In this study we will investigate TC induced OHU and ocean heat transport using a coupled ocean-atmosphere model, which will enable us to explore the impact of higher intensity TCs on the ocean. In this study, category 4, long-lived Hurricane Florence (30 Aug – 18 Sep 2018) is simulated using the atmosphere-ocean part of the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modelling system.  The entire track of Hurricane Florence across the North Atlantic basin is simulated using the high-resolution Advanced Research WRF (ARW-WRF) model and compared to the National Hurricane Centre best track archive. The model configuration, the composition of physical and cumulus parameterizations, the resolution of the SST reanalysis products and sensitivity to nudging and the number of vertical levels are investigated to produce a simulation that is as close to the best track as possible. The final simulation has an average track bias of less than 47 km and root-mean-square error (RMSE) intensity of less than 20 knots over the 15-day simulation. Next, the ocean response to Florence is simulated by using the ARW-WRF output as the driver to the Regional Ocean Modelling System (ROMS) and compared to observations.  In this presentation the ocean response to the simulated Hurricane Florence category 4 forcing will be discussed.

Effects of Topography and Sea Surface Temperature Anomalies on Heavy Rainfall Induced by Typhoon Chaba in 2016

Woojin CHO#+, Jinyoung PARK, Dong-Hyun CHA
Ulsan National Institute of Science and Technology, Korea, South

Typhoon Chaba made landfall on the Korean Peninsula in the fall of 2016 resulting in record-breaking rainfall in southeastern Korea. In particular, the Ulsan metropolitan region experienced the most severe floods due to heavy rainfall of 319 mm for just 3 h. The heavy rainfall was possibly associated with the mountainous southeastern Korea topography and the warm sea surface temperature (SST) anomaly in the East China Sea. In this study, the Weather Research and Forecasting (WRF) model was used to investigate the effects of topography and SST anomalies through high-resolution numerical experiments. Simulation using original topography showed more rainfall on windward and less on leeward slope compared to the experiment with reduced topography around Ulsan. The moist flow in the typhoon was raised by orographic uplift, enhancing precipitation on the windward side and summit of the mountains. The orographically induced updraft extended to the mid-troposphere and contributed to the upward vertical moisture flux associated with rainfall. Therefore, the mountainous topography around Ulsan affected the local change in rainfall induced by the simulated typhoon. In addition, SST on the track of the typhoon controlled the storm intensity and caused extreme precipitation changes. The experiment using the original SST in the East China Sea simulated less decayed typhoons and produced more precipitation compared to the experiment wherein the positive SST anomaly in the East China Sea was removed. The warm SST anomaly hindered the weakening of the typhoon moving northward to the mid-latitudes. At landfall, the stronger typhoon contained more water vapor, transported more moisture inland, and generated increased precipitation.

A Tale of Two Tropical Cyclones Affected by Volcanic Aerosols: Wukong (2018) and Cody (2022)

Haiyang LIU1, Xiaodong TANG1#+, Jian-Feng GU2
1Nanjing University, China, 2University of Reading, United Kingdom

The number of tropical cyclones (TCs) over the western North Pacific from June to August 2018 ranks second since the satellite era. Was this related to the continuous eruption of the Kilauea volcano at Hawaii from May to August 2018? The role of volcanic aerosols on tropical cyclogenesis has not yet been clearly understood and remains one of the important factors that impede our understanding on the climatological response of TC activity to volcanic aerosols. The impacts of volcanic aerosols from the eruption of the Kilauea volcano on the genesis of Typhoon Wukong in 2018 are investigated by numerical simulations with/without aerosol−cloud−radiation interactions. With only aerosol−radiation effect included, the radiative cooling at the low levels and heating above by aerosols induced stable sinking and decreased latent heating in Wukong’s environment. As a result, the sea-level pressure increased in the outer region, enhancing low-level radial inflow, inner-core convection and the release of latent heating, which was conducive to TC genesis. Further including the aerosol−cloud effect shows that the volcanic aerosols in TC circulation could be converted into cloud condensation nuclei, subsequently invigorating peripheral convection. The vigorous peripheral clouds draw more ascending air at the periphery of the storm, thereby weakening the low-level inflow toward the eyewall, which is not favorable for TC genesis. Only the experiments that include both radiation and aerosol−cloud effects of volcanic aerosols can reasonably capture the timing of TC genesis.TC Cody was very near the Hunga Tonga–Hunga Ha‘apai volcano during the eruption on 15 January 2022. The comparison of the effects of volcanic aerosols between on Cody (2022) and on Wukong (2018) will also be presented on the conference. This study may also have implications for exploring the impact of aerosols on potential changes in the regional and global climatology of TC activities.

Tue-02 Aug | 08:00 - 09:30 | MR06
AS28 - Global Precipitation Measurement, Science, and Applications

Session Chair(s): Takuji KUBOTA, Japan Aerospace Exploration Agency, George J. HUFFMAN, National Aeronautics and Space Administration, Goddard Space Flight Center, Yukari TAKAYABU, The University of Tokyo

AS28-A011 | Invited
Comparison of the Precipitation Rate Estimates Between TRMM/PR and GPM/KuPR

Shinta SETO#+
Nagasaki University, Japan

For over 20 years, precipitation measurement has continued with spaceborne radars including the Precipitation Radar (PR) operating at 13.8 GHz on the Tropical Rainfall Measuring Mission and the Ku-band Precipitation Radar (KuPR) operating at 13.6 GHz on the Global Precipitation Measurement mission core satellite. PR and KuPR have essentially the same hardware designs and the same algorithm to make standard products (PR Version 8 and KuPR Version 06, respectively). The surface precipitation rate estimates (R) and related variables are statistically compared between PR and KuPR for a common observation area (within 35oN and 35oS) and period (April to September 2014). Because the effects of sidelobe clutter in KuPR and beam mismatch in PR remain at some angle bins, the data at angle bins between 1 and 24 (excluding 20) are used in this analysis. Due to the difference in sensitivity, the total precipitation amount recorded by KuPR is larger than recorded by PR by approximately 1.3%. For the analysis of a long-term dataset connecting PR and KuPR, it is worth noting that the precipitation amount calculated for all data is affected by the difference of sensitivity. Calculation of the precipitation amount for samples with the same exceedance probability is an alternative idea. For heavy precipitation, PR shows a smaller measured radar reflectivity factor (Zm) and a larger R than KuPR. Zm is affected by the attenuation and it is smaller for PR than KuPR, as the frequency is slightly higher. The attenuation corrected radar reflectivity factor is almost the same for PR and KuPR. However, the adjustment factor is larger for PR, which results in a larger R.  Next, PR and KuPR are compared in matchup cases where the orbits of the TRMM and GPM core satellite cross each other within 1 minute and similar results are obtained.    

Development of Precipitation Detection Method for Spaceborne Precipitation Radar Using Dual-frequency Observations

Riku SHIMIZU1#+, Shoichi SHIGE1, Toshio IGUCHI2, Cheng-Ku YU3
1Kyoto University, Japan, 2Maryland University, United States, 3National Taiwan University, Taiwan

Spaceborne precipitation radars cannot observe precipitation at low altitudes near the ground contaminated by surface clutter, that is called blind zone. They estimate clutter free bottom (CFB) which is the lowest altitude not included in the blind zone, and observe precipitation at altitudes higher than CFB. High CFB over mountainous area is an obstacle to the detection of shallow precipitation and the estimation of low-level enhanced precipitation, which are common over mountainous areas. The Dual-frequency Precipitation Radar (DPR) onboard the GPM Core Observatory consists of a Ku-band radar (KuPR) and a Ka-band radar (KaPR). We compared data of KuPR, which is more sensitive than KaPR, with data of rain gauges over the mountainous area in northern Taiwan. We found five cases which KuPR missed near-nadir rainfall over 10mm/h observed by rain gauges because CFB was estimated to be higher than actual by KuPR. In this study, we improved the detection and estimation of precipitation by improving the CFB estimation algorithm and narrowing the blind zone. In the current standard algorithm, CFB was estimated using only the received power value data of KuPR. In this study, the CFB was estimated using the received power value data of both KuPR and KaPR. By lowering the CFB, KuPR succeeded in the detection of missed precipitation and the estimation of underestimated precipitation.

Temporal Variation of Incidence-angle Differences in Precipitation as Observed by Spaceborne Radars

Masafumi HIROSE1#+, Shoichi SHIGE2
1Meijo University, Japan, 2Kyoto University, Japan

The long-term spaceborne radar data provide a clear representation of the geographic distribution of precipitation. The orographic precipitation with a strong interference from surface clutter has a larger error than that of precipitation in flat areas. The errors caused by sensors and observation patterns vary depending on precipitation structure and occurrence frequency, and can affect the spatial distribution and temporal variation of mean values. In this study, we investigated the temporal variation of the difference in the statistics among the incidence angles of spaceborne precipitation radars to understand the impacts of the uncertainties associated with the observation limit, such as the error of the vertical distribution of precipitation at low levels and the missing of shallow precipitation, on the seasonal and diurnal variation of precipitation. The correction for the low-level precipitation profile is highly effective at high latitudes and the mountainous areas at which the most storm top height is less than 3 km. Moreover, uncertainties vary with the temporal variation of the storm top height. Note that the correction effect is weakened in the areas where the most storm top heights are below 1.5 km. For the correction of the shallow precipitation deficiency due to surface clutter (SPD correction), the deficit is estimated by relating the fraction of shallow precipitation and the bottom level free from clutter (CFB level). The CFB level varies greatly over a distance of 1 km in some steep mountainous areas. The percentage of shallow precipitation significantly varies with time. When the fraction of shallow precipitation is 60%, an SPD correction of 100% is required, resulting in an error exceeding the estimated value at high elevations. The vertical profiles just below the CFB level near the nadir, the errors below sensitivity, and the instantaneous estimates need to be separately considered with other observation data.

AS28-A009 | Invited
Early Results From GPCP Version 3.2 Products

George J. HUFFMAN1#+, David BOLVIN2, Eric NELKIN2, Guojun GU3, Mohammad Reza EHSANI4
1National Aeronautics and Space Administration, Goddard Space Flight Center, United States, 2Science Systems and Applications, Inc., United States, 3University of Maryland, United States, 4University of Arizona, United States

While the recent “golden age” of precipitation-relevant satellite sensors has provided unprecedented global information, the need continues for long-term climate-oriented precipitation products that emphasize homogeneity (Climate Data Records). The Global Precipitation Climatology Project (GPCP) products have addressed this need for several decades, and were upgraded in early 2022 to Version 3.2. Compared to the current operational versions (V2.3 [monthly], V1.3 [daily]), the spatial resolution has been improved to 0.5°x0.5°, geosynchronous infrared coverage is extended to 58°N-S, the Television-Infrared Operational Satellite (TIROS) Operational Vertical Sounder (TOVS) and Advanced Infrared Sounder (AIRS) records at high latitudes have been intercalibrated more effectively, climatologies based on recent satellite data (CloudSat, the Tropical Rainfall Measuring Mission, and the Global Precipitation Measurement [GPM] mission) are used, and regional modifications are applied to the gauge undercatch correction. Analysis of the previous Version 3.1 Monthly data verified useful finer-scale detail, and resolved a suspected artifact in the Southern Ocean around 60°S. However, strong interannual variation in tropical ocean regions and calibration differences between the Special Sensor Microwave Imager (SSMI) and Special Sensor Microwave Imager/Sounder (SSMIS) epochs appeared to stem from the Goddard Profiling (GPROF) algorithm. Additional calibration by the monthly Microwave Emission brightness Temperature Histogram (METH) estimates over ocean for the latitude band 25°N-S, tapered to no adjustment at 45°N,S controlled these issues. The Version 3 Daily product uses daily Integrated Multi-satellitE Retrievals for GPM (IMERG) over 55°N-S, with TOVS/AIRS at higher latitudes, all locally scaled to approximately sum to the V3.2 Monthly for consistency. The Monthly and Daily product periods of record are currently 1983-2020 and 2001-2020, respectively. The presentation will summarize early results, and consider the future satellites/sensors necessary to continue computation of a consistent CDR product.

Improvements of Global Satellite Mapping of Precipitation (GSMaP) Product Released in December 2021

Takuji KUBOTA1#+, Kazumasa AONASHI2, Tomoo USHIO3, Shoichi SHIGE2, Moeka YAMAJI1, Munehisa K. YAMAMOTO1, Hitoshi HIROSE1, Yukari TAKAYABU4
1Japan Aerospace Exploration Agency, Japan, 2Kyoto University, Japan, 3Osaka University, Japan, 4The University of Tokyo, Japan

The Global Satellite Mapping for Precipitation (GSMaP) produces high-resolution and highfrequent global rainfall map based on multi-satellite passive microwave radiometer (PMW) observations with information from the Geostationary InfraRed (IR) instruments (Kubota et al. 2020). Output product of GSMaP algorithm is 0.1-degree grid for horizontal resolution and 1-hour for temporal resolution. The GSMaP near-real-time version product (GSMaP_NRT) has been in operation at JAXA since November 2007 in near-real-time basis, and browse images and binary data available at JAXA GSMaP website (http://sharaku.eorc.jaxa.jp/GSMaP/). A new version of the GSMaP product was released in December 2021. We plan the reprocessing of the GSMaP standard version in a period during the past 24 years since Jan. 1998. Features in the new version are summarized as follows. In the PMW algorithm, retrievals extended to the pole-to-pole. Databases used in the algorithm were updated. A method using frozen precipitation depths was newly installed (Aonashi et al. 2021). Heavy orographic rainfall retrievals were improved upon a basic idea of Shige and Kummerow (2016). The normalization module for PMW retrievals (Yamamoto and Kubota 2020) were newly implemented to make more homogeneous PMW retrievals, in particular, for microwave sounders. A basic idea of the PMW-IR combined algorithm is using morphing and Kalman filter (Ushio et al. 2009). In addition, a histogram matching method by Hirose et al. (2022) was implemented in the new version to reduce the IR retrievals with reference to the PMW retrievals. In the gauge-adjustment algorithm, a precipitation estimate is adjusted using the NOAA CPC Global Unified Gauge-Based Analysis of Daily Precipitation (Mega et al. 2019). Artificial patterns appeared in past versions were mitigated in the new version. Preliminary validation results using the gauge-adjustment ground radar data over the Japan land areas confirmed better results in the new version of the satellite-only products.

Introduction of a Histogram Matching Method to Provide More Homogeneous GSMaP Products

Hitoshi HIROSE1#+, Takuji KUBOTA1, Tomoaki MEGA2, Tomoo USHIO2
1Japan Aerospace Exploration Agency, Japan, 2Osaka University, Japan

To compensate for the lack of observation network by passive microwave radiometer (PMW) onboard polar-orbiting satellites, the Global Satellite Mapping of Precipitation (GSMaP) uses infrared (IR) radiometers onboard geostationary meteorological satellites (GEOs). However, it was found that the GSMaP tended to overestimate rain rate in the GEO observing area as compared to that in the PMW observing area. A histogram matching method was introduced in the major update of the GSMaP algorithm in December 2021 for reducing the accuracy difference between PMW and GEO IR products. This method corrected the rain rate distribution in GEO IR observing areas to match the rain rate distribution in PMW observing areas. The rain rate in the GEO IR observing area was reduced by the correction, and the gap between GEO IR and PMW observing areas was also reduced. The case study analysis in the tropics showed that most of the rain overestimation of the GEO IR product occurred in upper-level clouds in the tropics, and the correction removed most of the overestimation. On the contrary, the GEO IR product tends to underestimate the rain rate from middle or lower-level clouds. Even after applying histogram matching, this underestimation tendency could not be completely removed. This is probably due to the difficulty of correcting rain overestimation for upper-level clouds and rain underestimation for middle or lower-level clouds at the same time. In this study, we developed an improved method of classifying upper clouds and middle or lower-level clouds based on cloud top temperature, and applying histogram matching methods to each cloud separately. The improved histogram matching method reduced the rain underestimation tendency of the GEO IR product for middle or lower-level clouds. The introduction of this improved method in the GSMaP algorithm update after 2022 is expected to provide more homogeneous GSMaP products.

Tue-02 Aug | 08:00 - 09:30 | MR02
AS25 - Dynamics and Prediction of Multi-scale Climate Variabilities Over Asia-pacific Region

Session Chair(s): Lu WANG, Nanjing University of Information Science & Technology, Feng HU, Chuzhou University

AS25-A001 | Invited
Synergistic Effect of the 25–60-day Tropical and Mid-latitude Intraseasonal Oscillations on the Persistently Severe Yangtze Floods

Jianying LI1#+, Panmao ZHAI1, Jiangyu MAO2
1Chinese Academy of Meteorological Sciences, China, 2Chinese Academy of Sciences, China

Significant 25–60-day intraseasonal oscillations (ISOs) in rainfall over the middle–lower reaches of the Yangtze River (MLYR) are found for 8 summers during 1979–2020. These 25–60-day ISOs of MLYR rainfall account for 66.7% of persistently severe floods (PSFs) during 1979–2020, indicating their major role in inducing PSFs and the potential for extended-range forecasting of PSFs. The 25–60-day ISO in MLYR rainfall results from the synergistic effect of tropical and mid-latitude ISOs. During the 8 identified summers, more barotropic energy is transferred from summer-mean to 25–60-day circulation, thus forming a mid-latitude ISO wave train, which cooperates with the tropical ISO in triggering twin vertical cells. Phase locking of ascending branch from the vertical cell induced by the tropical ISO with that from the reversed vertical cell triggered by the mid-latitude ISO brings about the wet phase of 25–60-day ISO of MLYR rainfall.

AS25-A008 | Invited
The Combined Effects of the Tropical and Extratropical Quasi-biweekly Variabilities in Modulating the Record-setting Meiyu Rainfall in 2020

Shuanglin LI#+, Zhen HUANG
China University of Geosciences, China

During June–July 2020, record strongest Meiyu rainfall occurred in the Middle and Lower reaches of Yangtze River (MLYR). The rainfall processes exhibited an obvious quasi-biweekly (biweekly in brief) variability, and there are altogether five biweekly cycles identified. It is found first that the biweekly rainfall mainly arises from the collaborative effects of biweekly activities from both the tropics and extratropics. As for the tropics, the biweekly meridional march and retreat of the western Pacific subtropical high (WPSH) is particularly evident. As for the extratropics, geopotential height anomalies near Lake Baikal are specially active at biweekly timescale. Further, the former is attributed to the intensified biweekly activity of the southwest-northeast oriented East-Asian Pacific pattern-like wavetrain (EAP) originating from the tropical western Pacific, while the latter is associated with the biweekly activities of the Eurasia mid-high latitudinal wavetrain and the North Pacific westward wavetrain. The three wavetrains meet over East Asia, causing intensified convergence (divergence) and subsequently the wet (dry) phase of biweekly rainfall. Why the biweekly activities of the three wavetrains specially intensified in 2020 is further diagnosed from the perspective of thermodynamical forcing and also from the modulation of interannual background on intraseasonal variability. It is found that the record-strongest convection anchored over the tropical western Indian Ocean (IO) in summer 2020. The associated diabatic heating triggers anomalous descent over the tropical western Pacific, which modulates the biweekly activity of EAP. Meanwhile, the anomalous tropical diabatic heating over IO causes changes of the meridional thermodynamic contrast across the tropical IO to high-latitudes, which modulates the biweekly geopotential height anomalies near Lake Baikal. This study highlights the role of the record strongest convection over IO in modulating the record strongest Meiyu rainfall in 2020.

Causes of Interdecadal Increase in the Intraseasonal Rainfall Variability Over Southern China Around the Early 1990s

Yifeng CHENG1+, Lu WANG1#, Tim LI2
1Nanjing University of Information Science & Technology, China, 2University of Hawaii, United States

The southern China (SC) summer rainfall exhibits prominent intraseasonal variability, which exhibits a significant increase in the early 1990s with the turning point at 1993. The SC intraseasonal rainfall events could be divided into three categories according to different propagations, including the southward-propagating (SP) events, the northwestward-propagating (NWP) events, and the northward-propagating (NP) events. This study explores the causes of the observed interdecadal increase in the intraseasonal rainfall variability over SC by comparing the SC intraseasonal rainfall events of each category between the former decadal period (P1) and the later decadal period (P2). The result indicates that such interdecadal change is due to the more frequent NP events coming from the South China Sea (SCS). Based on the moisture and vorticity budget analysis, it is revealed that the summer mean southerly wind in the middle to lower troposphere is the dominant factor of the northward propagation over the SCS, as it could induce positive meridional moisture and vorticity advection anomalies ahead of the convection. A marked interdecadal enhancement of the summer
mean southerly wind over the SCS is the cause of more frequent occurrence of NP events over SC, as it provides more favorable conditions for the northward propagation. The change of the atmospheric instability over the SCS where the NP convection perturbation originates was also investigated, but no significant change was found

Subseasonal and Synoptic Variabilities of Precipitation Over the Yangtze River Basin in the Summer of 2020

Liudan DING#+
Nanjing University of Information Science & Technology, China

Summer precipitation over the Yangtze River basin (YRB) in 2020 experienced a strong subseasonal and synoptic fluctuation in addition to contributing to an exceptionally large seasonal mean precipitation. The cause of this higher-frequency fluctuation is examined based on observational analyses. Apart from the continuous northward movement of the climatological mei-yu rainband, the mei-yu rainbelt in the summer of 2020 experienced multiple northward and southward swings. The cause of the swings was attributed to the subseasonal variability of southerly winds to the south and northeasterly winds to the north of the YRB. In addition, synoptic-scale variability, characterized by the eastward propagation of low-level cyclonic vorticity and precipitation anomalies, was also commonplace in the summer of 2020. While the strengthening of both the subseasonal and synoptic variabilities in the summer of 2020 was attributed to the increase of the background mean moisture, the synoptic variability was greatly affected by the subseasonal rainfall variability. As a result, both the synoptic-scale and subseasonal variabilities contributed to the north-south swings of the rainbelt. The large-scale modulations by both the seasonal mean and subseasonal anomalies provide insight regarding the optimization of issuing accurate, extended-range forecasts of extreme weather events.

The Independent Influences of Sea Surface Temperature Anomalies Over the Atlantic on the Interannual Variability of East Asian Summer Monsoon Rainfall

Ying YANG1#+, Zhiwei ZHU1, Tim LI2, Leishan JIANG1
1Nanjing University of Information Science & Technology, China, 2University of Hawaii, United States

As the most dominant tropical climate mode on the interannual timescale, El Niño-Southern Oscillation (ENSO) is suggested to significantly influence the interannual variation of East Asian summer monsoon rainfall (EASMRI). However, the leading mode of EASMRI remains almost untouched when the impacts of preceding ENSO events are linearly removed, suggesting the existence of alternative impact factors and predictability sources of EASMRI.
After removing the impact of ENSO, the sea surface temperature anomalies (SSTAs) over both the tropical Atlantic and extratropical North Atlantic are found to be related with EASMRI via atmospheric teleconnections. Positive SSTA over the tropical Atlantic could induce tropical diabatic heating, which triggers an equivalent barotropic Rossby wave train emitting from the Atlantic, going across the Eurasian continent and ending with a cyclonic anomaly over northeast Asia. The tropical diabatic heating could also induce western North Pacific anomalous anticyclone via a tropical route. The dipole SSTA pattern with cooling in the west and warming in the east over the extratropical North Atlantic induces local circulation anomalies via heat flux exchange, which could further perturb a Rossby wave train with a cyclonic anomaly over northeast Asia, thus modulating EASMRI. Numerical experiments with prescribed atmospheric heating associated with Atlantic SSTAs could realistically reproduce these teleconnections of EASMRI.
By adding the predictability sources of Atlantic SSTAs, the seasonal prediction skills of EASMRI could be significantly improved over both the tropical western North Pacific and subtropical land regions such as central China and Japan.

Prediction Skill of Intraseasonal Surface Air Temperature Over Mid-high-latitude Eurasia in S2S Models

Jing CUI1#+, Shuangyan YANG1, Tim LI2
1Nanjing University of Information Science & Technology, China, 2University of Hawaii, United States

The subseasonal to seasonal (S2S) prediction is the skill gap between the more mature weather and climate prediction and it has been long regarded as a “desert of predictability”. More and more progress has been made to bridge the gap between weather and climate prediction, such as the S2S prediction project launched by WWRP and WCRP. The atmospheric intraseasonal oscillation (ISO) is taken as a major source of subseasonal predictability. In this study, we mainly focus on the dominant ISO modes of surface air temperature (SAT) over mid-high-latitude Eurasia (MHLE), together with the systematic assessment of its prediction skill in some state-of-the-art S2S models. Features of the intraseasonal SAT over MHLE during boreal winter and summer are captured with the observational SAT anomalies by EOF analysis. Each cycle of the southeastward/eastward-propagating ISO of SAT is divided into eight phases formed by the first two principal components. Reforecast data from S2S models are utilized to assess the prediction skill of the ISO based on the PC index. Upper limit of useful forecast skill ranges from ~10 to ~20 days and models display better skill for target strong cases, although they systematically underestimate the amplitude of the intraseasonal signal. Generally, the ECMWF model exhibits the best score. Skill-dependent feature on target phases is commonly found in theses S2S models and it is probably associated with the phase-dependence of amplitude bias and phase angle error, indicating the importance of skillfully predicting ISO amplitude and propagation speed. Analysis of potential predictability based on perfect-model assumption shows a 4~6 day skill gap for most of the S2S models. The results imply the potential and need for the continued development of operational forecasting systems to facilitate more accurate and longer-lead predictions of the ISO signal over MHLE.

Tue-02 Aug | 10:00 - 11:30 | MR01
AS08 - Future of Cities within the Context of Climate Change

Session Chair(s): Quang-Van DOAN, University of Tsukuba

City-scale Large Eddy Simulation Model (City-LES) to Propose Better Adaptation Strategies for Heat Stress Mitigation in Urban Areas

Hiroyuki KUSAKA1#+, Takuto SATO1, Ryosaku IKEDA2, Satoru IIZUKA3, Taisuke BOKU1
1University of Tsukuba, Japan, 2Weathernews Inc, Japan, 3Nagoya University, Japan

Meso-scale and micro-scale meteorological models have been largely contributing to urban climatology. This talk will introduce highlights of city-scale meteorological modeling efforts by our group, specifically the new version of our own city-scale large eddy simulation (LES) model named City-LES (Ikeda et al. 2015). The main features of this model are as follows. (1) This model numerically and three-dimensionally simulates/predicts the time-varying spatial distributions of fluid, radiations, and cloud/fog formation. (2) The dynamics core is based on non-hydrostatic Boussinesq approximation equations and the model considers atmospheric static stability. (3) The spatial resolution of the model is in order of 1 to 10 m and the model can resolve buildings and roadside trees. (4) Long- and short-wave radiations are calculated three-dimensionally and multiple reflections of the radiations within urban canopy layers are considered by the radiosity method. (5) Using the model, we can evaluate the various mitigation strategies of uncomfortable thermal environments, for instance, installation of dry-mist spraying, roadside trees, cool pavements, and green/cool roofs. (6) The model outputs various heat stress indices (UTCI, WBGT, PMV, MRT). (7) The model simulations are performed with the dynamical downscaling from mesoscale meteorological models such as the WRF model. (8) There are two versions of programming code: CPU code and GPU code versions. The GPU version is faster, taking only one-sixth to up to one-fifteenth the computation time of the CPU version. The talk will include simulation results, as well as the development of the City-LES model.

Measuring the Urban Heat Advection in London, England with Citizen Weather Stations

Oscar BROUSSE1#+, Charles SIMPSON1, Nancy WALKER2, Daniel FENNER3, Fred MEIER4, Jonathon TAYLOR5, Clare HEAVISIDE1
1University College London, United Kingdom, 2University of Southampton, United Kingdom, 3University of Freiburg, Germany, 4Technische Universität Berlin, Germany, 5Tampere University, Finland

Urban heat advection (UHA) is often neglected in urban climate studies, despite its impact on heat’s spatial distribution in cities, as it is challenging to directly measure. In this study, we propose for the first time a method to quantify UHA in cities using 6-year (2015-2020) hourly measurements of air temperature from a network of quality-checked citizen weather stations (CWS) and the Local Climate Zones land use land cover classification. We define a domain centered over London that is divided in four cardinal quadrants for studying the urban heat advection. We extract prevailing wind conditions, based on direction and speed, using hourly measurements from the Heathrow Airport automatic weather station. We consider UHA to be the heat anomaly measured at each CWS located in the downwind quadrant compared to the average temperature measured in all CWS located in a similar Local Climate Zone of the upwind quadrant. We remove systematic urban heat related to local land-atmosphere interactions in the temperature measurements by subtracting time-averaged temperature at each CWS from each hourly measurement. Results show an averaged UHA of ∼0.22°C in downwind quadrants of London compared to upwind quadrants. Yet, the measured anomaly related to UHA at each CWS location can be both positive and negative by up to ∼2.0 °C or down to ∼-1.0 °C, respectively. This suggests important microclimatic effects happening at each location. In general, CWS can help understanding the spatio-temporal variability of UHA. Future studies on the microclimatological effects that explain the presence of both negative and positive values in downwind quadrants are needed. Lastly, we argue that UHA should be considered in future adaptative and mitigative urban planning strategies.

Wind Field of a Realistic Dense City by Large-eddy Simulation

Lan YAO+, Chun-Ho LIU#
The University of Hong Kong, Hong Kong SAR

Atmospheric surface layer (ASL) flow governs the urban air exchange - pollutant transfer process. For cities, especially with dense buildings, it is necessary to understand how the flow behaviors are strongly perturbed by diversified obstacle configurations. The outcome could benefit urban planning towards improved city-scale ventilation. In this study, large-eddy simulation (LES) was conducted to study the flows over Kowloon Peninsula (buildings footprint extends to 8km and 10 km along east-west and north-south directions), Hong Kong. The built environment concerned is one of the most densely populated cities in the world. It consists of more than 3,000 buildings with height over 100 m. In view of the blockage, the mean flow could be diverted from the prescribed wind direction within 30o to 50o. The conventional law-of-the-wall (log-law) for boundary-layer theory was applied to identify the inertial sublayer (ISL) for different urban morphologies. The aerodynamic parameters (i.e., roughness length, z0, and zero-height displacement, d) and friction velocity (uτ) demonstrated a measure of roughness degree (rougher surfaces, larger z0 and uτ). Moreover, rougher surfaces manifested lower dimensionless log-law region and slower dimensionless wind speed in the roughness sublayer (RSL). Another observation, which was different from those fabricated by idealized geometries, was an elevated giant wake induced by high-rise building clusters, coincident with the twin-peaks of the averaged vertical profiles of turbulent momentum flux. Besides, this wake could implicate non-negligible dispersive momentum transport, enhancing turbulent mixing and ventilation. These results characterize the flow over realistic buildings compared with that over homogeneous roughness. The preliminary explorations could help further improve meteorological models, and advance urban planning for dense-built cities.

The Impact of Urban-scale Grid on the Representation of the Urban Convective Boundary Layer Over Singapore

Song CHEN1,2#+, Pratiman PATEL3, Anurag DIPANKAR4, Matthias ROTH3, Aurel MOISE1
1Centre for Climate Research Singapore, Singapore, 2Meteorological Service Singapore, Singapore, 3National University of Singapore, Singapore, 4ETH Zurich, Switzerland

Increasing interest in high-resolution forecasts of meteorological hazards in cities (e.g., urban heat island, flash flood, and air pollution) at both weather and climate time scales has driven the development of urban-scale models at 25-300m resolution. These high-resolution models allow for a better representation of urban environments and their impacts on the atmosphere, and they are also expected to better resolve turbulence processes and the structure of urban boundary layers. One key issue for such high-resolution urban models is to understand the behavior of the urban convective boundary layer, which is rarely studied, especially in tropical areas. In this work, we perform a numerical study using the urban version of the Singapore Meteorological Service’s numerical weather prediction system (uSINGV) to investigate the impact of model grid resolution (1500m, 300m, and 100m) on the representation of the urban boundary layer over Singapore. For simplicity the slab model is adopted to characterize the urban surface, to be able to focus on the effects of the native model grid. Boundary layer profiles and near-surface meteorological parameters are compared across different grid resolutions. Spin-up artifacts arising from the inflow boundary are analyzed. Finally, the numerical results are compared with observed atmospheric profiles to evaluate the added value of high-resolution models.

Influence of Urban Topographical Indices on Ventilation Timescales

Guangdong DUAN1#+, Kumi NAKAMAE2, Tetsuya TAKEMI2
1Dalian Maritime University, China, 2Kyoto University, Japan

Ventilation improves in urban regions of high non-uniformity [Lo & Ngan, Boundary-layer Meteorology, 122(2015), 611-621]; however, it remains unclear how the ventilation timescales are affected by the topographical indices, e.g. building packing densities (𝛌f and 𝛌p for the frontal and plan area, respectively) that commonly adopted for the characterization of urban 3-D profiles. Using large-eddy simulation (LES), the dispersion of a passive pollutant scalar from an instantaneous source is investigated for turbulent boundary-layer (TBL) flows developed over realistic urban regions. While the decay of the domain averaged concentrations follow the familiar exponential [Duan et al., Environmental Fluid Mechanics, 19(2019), 911-939] for all cases, the decay rate exhibits a clear dependence on 𝛌f. The mean tracer age, 𝛕a, which has proven an effective probe to the Lagrangian nature of a passive scalar in TBL flows [Duan & Ngan, Building and Environment, 183(2020), 106969], shows a strong linear scaling with 𝛌f (R2=0.8 using least squares regression). Similar scaling is seen for 𝛕a with the mean building height, Have (R2=0.7), but a clear trend is hard to be discerned for 𝛕a versus the other topographical indices (e.g. 𝛌p and the building height variability, σH). Possible reasons are discussed. The results enable the parameterization of ventilation timescales for complex urban topographies and could be useful for urban design of optimized active ventilation capability.

A Quantification of Classic But Unquantified Positive Feedback Effects in the Urban-building-energy-climate System

Yukihiro KIKEGAWA1#+, Yuya TAKANE2, Yukitaka OHASHI3, Tomohiko IHARA4
1Meisei University, Japan, 2National Institute of Advanced Industrial Science and Technology, Japan, 3Okayama University of Science, Japan, 4The University of Tokyo, Japan

The interaction between urban air temperature (T) and building cooling energy demand (E) generates a well-known positive feedback (PFB), which is mediated by sensible anthropogenic heat (Qfs) and named Qfs-T-E PFB in this study. This PFB could induce self-reinforced warming, but its effects have not been completely quantified. Hence, this study aimed to clarify these effects by targeting Osaka, a Japanese major city. Focusing on the from-weekends-to-weekdays increase in urban energy consumption including E increase as an observable trigger of the PFB, its induced T rise due to growth in Qfs was estimated with the fed-back additional E gain on weekdays based on observed ground-level T and district-wise electric power consumption during summer. The result indicated that the weekdays–weekends contrast in energy consumption over Osaka could induce the Qfs-T-E PFB effects, which resulted in fed-back E gain reaching 10% on weekdays. Such observational PFB impact on E was found to be reproducible by the proposed urban meteorological model, named WRF-CM-BEM. Thus, the validated model was applied to the quantification of the PFB impact on T based on feedback gain (gA) which means a percentage of T variation caused by the PFB. An attempt was made to quantify gA through the two-cases simulations of the weekdays-run and holidays-run for the months of August in 10 years. The simulations provided estimates on gA, whose daytime averages reached nearly 10% in the downtown commercial areas and 20% in the leeward-located residential areas, suggesting the influence of sea breeze heat advection of downtown Qfs. Such estimated impacts on T were roughly in the same order of magnitude compared to those in a few earlier studies that were not based on observational validations and seemed to be non-negligible, considering the feedback impacts on global surface warming estimated with gA of approximately 50% by IPCC.

Tue-02 Aug | 10:00 - 11:30 | MR07
AS09 - Observations, Remote Sensing, and Modeling of Tropospheric Composition and Air Quality in Asia and the Transpacific Region

Session Chair(s): Richard ECKMAN, National Aeronautics and Space Administration, Jun WANG, The University of Iowa

AS09-A014 | Invited
First Global Observation of Tropospheric Formaldehyde from Chinese Gaofen-5 Satellite: Locating Source of Volatile Organic Compounds

Wenjing SU+, Cheng LIU#
University of Science and Technology of China, China

Satellite remote sensing is an important technique providing long-term and large-scale information of formaldehyde (HCHO), which plays a crucial role in atmospheric chemistry. Low signal-to-noise ratio and poor stability of the Environmental Trace Gases Monitoring Instrument (EMI) On board Gaofen-5 satellite, the first Chinese space-borne spectrometer, make HCHO retrieval extremely difficult. Here we firstly retrieved HCHO vertical column densities (VCDs) from EMI through in-flight spectral calibration, retrieval setting optimization and stripe correction. Retrieved EMI HCHO VCDs correlate well with those measured by Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) with normalize mean bias (NMB) below 25%. EMI HCHO VCDs are comparable with those observed by Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI). This study reveals that HCHO can be observed successfully by algorithm optimization despite of poor performance of space-borne spectrometer. The retrieved EMI HCHO VCDs are applied to locate emission sources of volatile organic compounds (VOCs).

The Impact of Soil NOx Emissions on Air Quality in East China

Tong SHA#+
Shaanxi University of Science & Technology, China

Nitrogen oxides (NOx) are known as critical air species forming ozone (O3) and nitrogen aerosols, influencing the atmospheric oxidizing capacity, deteriorating the air quality, and harming human health. Although stringent anthropogenic NOx emission controls have been implemented in recent years, observations show that the near-surface O3 concentrations over most regions in China are still increasing year by year. Intensive agricultural activities in East China can lead to substantial NOx emissions from soils, while this source is subject to being overlooked in previous studies and the role of soil NOx emissions (SNOx) on local air quality is unknown. In this study, WRF-Chem model coupled with the new scheme Berkeley Dalhousie Iowa Soil NO Parameterization (BDISNP) is used to investigate SNOx and its contribution to air pollution during a growing season as a case study. The model with BDISNP scheme shows a better agreement with TROPOMI NO2 column densities (columns), especially over croplands, and also improves the performance on simulating surface SO2, NO2, and PM2.5 concentrations in East China. Model simulations reveal that SNOx contribute to 34% (39%) of the total NOx budget in summer, such amounts of SNOx increase the mean NO2 columns by 33% (43%) and surface NO2 concentrations by 68% (69%), resulting in surface O3 concentrations in the daytime (13:00-16:00) increased by 14.6% (14.8%) in East China (over croplands). High SNOx could also aggravate aerosol pollution in this region, leading to the mean nitrate and PM2.5 concentrations increased by 27%-33% and 11%-16%, respectively. Our results highlight that NOx emissions from soils exert non-negligible impacts on the summertime air quality in East China and need to be considered in the emission abatement strategies.

Impacts of Aerosol-radiation Feedback on Air Quality Over Delhi, India

Lakhima CHUTIA#+, Jun WANG, Huanxin ZHANG
The University of Iowa, United States

The National Capital Region (NCR) of India, Delhi has experienced acute air pollution episodes, especially during the post-monsoon season, mainly attributed to crop residue burning. This study attempts to assess the impact of aerosol‐radiation feedback (ARF) on air quality and tropospheric chemistry during a pollution episode in November 2018 over NCR Delhi using the Unified Inputs (initial/boundary conditions) for WRF-Chem (UI-WRF-Chem) model. The UI-WRF-Chem uses MERRA-2 data to provide both meteorological and chemical initial and boundary conditions for regional WRF-Chem model. Here we conduct two model simulations with and without inclusion of aerosol-radiation feedback. Model captures the observed diurnal variability of fine particulate matter over Delhi with a significant reduction in mean bias (up to 20%) due to the inclusion of aerosol-radiation feedback. The aerosol-radiation interaction showed a substantial decrease in surface net downward shortwave radiation (31–62 W/m2) and air temperature (1-1.2º C); this, in turn, leads to a reduction in the surface energy budget (1-30 W/m2) and boundary layer height by 10–640m (15–57%). The shallower atmospheric boundary layer and weaker winds (2-40%) due to aerosol forcing further enhance the concentration of fine particulate matter by up to 26 μg/m3 (35%) and gaseous pollutants such as CO, SO2, NOx (2-38%) near the surface. Reduction in ozone concentration (10%) due to aerosol is found to be linked with the changes in NO/NO2 ratio and photolysis rates. The strong correlation between ARF-induced changes in relative humidity and aerosol optical depth indicates a positive feedback mechanism, wherein suppressed boundary layer and increased relative humidity (5-14%) due to aerosol forcing favors the accumulation of near-surface pollutant concentrations, further deteriorating the air quality. These aerosol-radiation interactions have important implications on the mitigation of higher pollution loading over NCR Delhi, especially during crop residue burning season.

A Top-down Method of Estimating NOx Emissions Over South, Southeast and East Asia Based on OMI NO2 Observations

Jian LIU1,2+, Jason COHEN2#
1Sun Yat-sen University, China, 2China University of Mining and Technology, China

Rapid changes in economics and urbanization, as well as increased biomass burning in South, Southeast, and East Asia, have led to emissions inventories missing or mis-categorizing significant sources of emissions in these regions. To comprehensively analyze data across such a diverse region, the uniformity and availability of remotely sensed measurements is essential. This work introduces a new approach to directly estimate emissions of NOx at daily-scale, as well as the underlying in-situ physical, chemical, and thermodynamic factors connecting the emissions with the observed column loadings. This approach is found to be mass-conserving, and is capable of capturing extreme events extremely well across both biomass burning and urban sources. Comparisons with existing a priori emissions from FINN and EDGAR-HTAPv2.2 are made, with differences in both space and time explained and quantified for the year 2016. This work’s “total emissions” of NO2 is found to be larger overall, but quite complex, with unidentified new sources observed, as well as mis-characterized existing sources, some of which are too high and others of which are too low. Significant underestimations in rural areas in Myanmar, Northern Thailand, Laos, and Northeast India, as well as in urban areas in the Pearl River Delta, Wuhan, Nanchang, Changsha, and Dhaka. Impacts of looking at month-to-month or year-to-year scales are further quantified. Uncertainties in the emissions estimates, including how the approach can be improved with new physics, chemical, and thermodynamic work, is further introduced.

Full-coverage Daily Ground-level Ozone Estimation from Bigdata Using Machine Learning Across China

Jing WEI1#+, Jun WANG2, Zhanqing LI1,3
1University of Maryland, United States, 2The University of Iowa, United States, 3Beijing Normal University, China

Ozone (O3) is an important trace and greenhouse gas in the atmosphere, posing a threat to the ecological environment and human health at the ground level. This study offers a new perspective to estimate ground-level O3 from solar radiation intensity and surface temperature by employing an extended ensemble learning of the space-time extremely randomized trees (STET) model, together with ground-based observations, remote sensing products, atmospheric reanalysis, and an emission inventory. A full-coverage (100%), high-resolution (10 km) and high-quality daily maximum 8-h average (MDA8) ground-level O3 dataset covering China (called ChinaHighO3) from 2013 to 2020 was generated. Our MDA8 O3 estimates (predictions) are reliable, with an average out-of-sample (out-of-station) coefficient of determination of 0.87 (0.80) and root-mean-square error of 17.10 (21.10) μg/m3 in China. The unique advantage of the full coverage of our dataset allowed us to accurately capture a short-term severe O3 pollution exposure event that took place from 23 April to 8 May in 2020. Also, a rapid increase and recovery of O3 concentrations associated with variations in anthropogenic emissions were seen during and after the COVID-19 lockdown, respectively. Trends in O3 concentration showed an average growth rate of 2.49 μg/m3/yr (p < 0.001) from 2013 to 2020, along with the continuous expansion of polluted areas exceeding the daily O3 standard (i.e., MDA8 O3 = 160 μg/m3). Summertime O3 concentrations and the probability of occurrence of daily O3 pollution have significantly increased since 2015, especially in the North China Plain and the main air pollution transmission belt (i.e., the “2 + 26” cities). However, a decline in both was seen in 2020, mainly due to the coordinated control of air pollution and ongoing COVID-19 effects.

Cropland Nitrogen Oxides Emissions and Effects on the Ozone Pollution in the North China Plain

Ruonan WANG1#+, Naifang BEI2, Guohui LI1, Xia LI1,3, Suixin LIU1, Jiaoyang YU1, Qian JIANG1, Xuexi TIE4
1Chinese Academy of Sciences, China, 2Xi’an Jiaotong University, China, 3University of Chinese Academy of Sciences, China, 4National Center for Atmospheric Research, United States

Soil nitrogen oxides (NOX = NO2 + NO) emissions have been measured and estimated to be the second most significant contributor to the NOX burden following the fossil fuel combustion source globally. NOX emissions from croplands are subject to being underestimated or overlooked in air pollution simulations of regional atmospheric chemistry models. With constraints of ground and space observations of NO2, the WRF-Chem model is used to investigate the cropland NOX emission and its contribution to the near-surface ozone (O3) pollution in North China Plain (NCP) during a growing season as a case study. Model simulations have revealed that the cropland NOX emissions are underestimated by around 80% without constraints of satellite measured NO2 column densities. The biogenic NOX source is estimated to account for half of the anthropogenic NOX emissions in the NCP during the growing season. Additionally, the cropland NOXsource contributes around 5.0% of the maximum daily average 8 hours O3 concentration and 27.7% of NO2 concentration in the NCP. Our results suggest the agriculture NOX emission exerts non-negligible impacts on the summertime air quality and needs to be considered when designing emission abatement strategies.

Tue-02 Aug | 10:00 - 11:30 | MR08
AS45 - Aviation Meteorology

Session Chair(s): Jung-Hoon KIM, Seoul National University

AS45-A013 | Invited
Effects of Distant Convection on Widespread Clear-Air Turbulence

Stanley TRIER#+
National Center for Atmospheric Research, United States

In this presentation I will document the role of distant convection on observed widespread strong clear-air turbulence near upper-level jet streams in different weather patterns. Results from nested NWP model simulations, together with similar examples from previous case studies, suggest a strong association of widespread turbulence with jet stream enhancements related to outflow from upstream convection. We demonstrate that model horizontal grid spacings of < 1 km are required to adequately resolve common turbulence onset mechanisms (e.g., Kelvin-Helmholtz instability, internal gravity wave breaking). However, examples are provided showing how turbulence forecasting systems driven by lower resolution operational NWP models can provide potentially valuable guidance on these widespread turbulence events when those models accurately forecast the timing and locations of upstream convection.

Automatic Aviation Turbulence Detection Using Advanced Machine Learning Techniques

James KWOK1#+, Lawrence CHAN1, Haitao YIN1, Peter Ping-Wah LI2, Christy YY LEUNG2
1Hong Kong University of Science and Technology, Hong Kong SAR, 2Hong Kong Observatory, Hong Kong SAR

Aviation turbulence can cause passenger and crew injuries, aircraft damage and bring disruption to airport operations. Turbulence ahead, especially clear air turbulence, is difficult to be detected with onboard instruments. To enhance aviation safety, this paper studies the use of machine learning techniques on meteorological data to automatically detect aviation turbulence. Data utilized in building the model includes multispectral geostationary meteorological satellite images, numerical prediction model (NWP) data and flight data in 2018-2020. The detection model has two components. The first is a modified residual network (ResNet-50), which takes satellite images as input to provide a three-class classification of the intensity, viz. nil/light, moderate or severe turbulence. The output labels are collected from pilot reports, Eddy Dissipation Rate (EDR) generated from aircraft quick access record data and Aircraft Meteorological Data Relay (AMDAR). To overcome the problems of data sparsity and class imbalance, the modified ResNet is pre-trained by self-supervised learning (using "Bootstrap your own latent") from unlabeled satellite images. The pre-trained model is then trained with data augmentation using transformations such as horizontal flip, color jitter, random resized crop, and Cutmix and the class-balanced label-distribution-aware margin loss. The second component is a convolutional neural network (CNN) with spatiotemporal convolutional blocks, which also takes in 18 turbulence indices derived from NWP model including Turbulence Index 2 (TI2), vertical wind shear, curvature, etc. Representations from the two model components are fused together by contrastive learning using "contrastive visual representation learning from text", which maximizes agreement of the representations learned individually from the two model components. Afterwards, a fully-connected layer is created and trained with the labeled data for turbulence intensity classification. The model significantly outperforms common turbulence diagnostic products such as TI2 with a F1-score of 80, 74 and 56 for the nil/light, moderate and severe class respectively.

Analysis of the Meteorological Fields in Aviation Accident Cases Due to Clear Air Turbulence

Hironobu UCHIDA1, Masatomo FUJIWARA1#+, Jung-Hoon KIM2, Robert SHARMAN3
1Hokkaido University, Japan, 2Seoul National University, Korea, South, 3National Center for Atmospheric Research, United States

Aviation turbulence causes unexpected motions of aircrafts such as shaking and rapid descending/ascending and threatens the safety of the aircraft operations. Clear air turbulence (CAT) is a type of aviation turbulence that occurs above the mid-troposphere under cloud-free conditions or within stratiform clouds. In this study, we investigate seasonality, geographical distribution, and the favored location within weather systems of aviation turbulence cases due to CAT by analyzing pilot reports (PIREPs) provided by US airlines in the year 2016 together with a new, very-high-resolution global atmospheric reanalysis data ERA5 (at one-hourly and at 0.25x0.25 degree horizontal resolution). First, using the PIREPs, seasonality and geographical distribution of aviation turbulence cases are described. Second, for some turbulence cases, correspondence among different turbulence indices (i.e., vertical shear of horizontal winds (Sv), horizontal deformation (DEF), and the Turbulence Index 1 (TI1= Sv x DEF )) calculated from ERA5 data is investigated. Third, statistical relationship between the turbulence index values from ERA5 and the turbulence intensity from PIREPs is investigated. Finally, a composite analysis of meteorological fields for turbulence events is conducted to find the regions of high chance of turbulence events.

A Numerical Simulation of a Coastal Fog Bank Event on Nova Scotia, Canada Using the WRF Model

Jeonghoe KIM1+, Jung-Hoon KIM1#, Clive DORMAN2
1Seoul National University, Korea, South, 2Scripps Institution of Oceanography, United States

Atlantic Canada is one of the regions where fog occurs most frequently over the world. A coastal fog bank event reported on 8 September 2021 next to Nova Scotia was investigated using the Weather Research and Forecasting (WRF) model version 4.3. A single domain positioned at the center of Nova Scotia was used with a model configuration of 2 km horizontal grid size, 10 m vertical spacing below 500 m, and the lowest level of 4.5 m. Hourly ERA5 reanalysis and OSTIA skin sea surface temperature (SST) analysis were used for initial and boundary conditions. Non-local turbulence closure of YSU scheme was selected for planetary boundary layer parameterization. Temperature and relative humidity simulated from the model were consistent with both the surface weather observations and RAOB data. Simulated total cloud water distribution captured well the unique structures of fog distribution observed by the GOES satellite images during the event and especially the fog bank on the southeast coast of Nova Scotia. Potential temperature tendency near surface indicated that advection of cloud water and resultant enhancement of longwave radiative cooling contributed the formation of the fog bank. Positive sensible and latent heat fluxes from the ocean caused the fog layer to grow. However, the vertical growth of the fog layer was limited due to the capping inversion just above the fog layer driven mainly by subsidence and differential advection. Back trajectory analysis suggested that cold air parcels moving offshore through inland areas also contributed the formation of the fog bank. Acknowledgement: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT)(No. NRF-2021R1A4A5032320).

Characteristics of Low-level Turbulence Observed by Unmanned Aerial Vehicle in Suburb of Seoul Metropolitan Area

Soo-Hyun KIM+, Jung-Hoon KIM#, Jeonghoe KIM, Jeongmin KIM, Jae-Sik MIN
Seoul National University, Korea, South

Given that the demand of unmanned aerial vehicle (UAV) is expected to increase rapidly, monitoring and understanding of low-altitude meteorological conditions are essential for safe and efficient flights of the UAV. For this purpose, a field campaign using drone equipped with the sonic anemometer was conducted in suburb of Seoul metropolitan area, South Korea during the summer (between 30 July and 29 August) in 2021 under the dominant synoptic-scale condition of heat wave due mainly to the expansion of the North Pacific High pressure in the research period. The drone measures wind at every second from the surface to the altitude of ~150 m with 30-second hovering segment at every 10-m altitude while climbing. The drone-observed data include 1-Hz horizontal wind velocity, positioning angles (pitch, roll, and yaw angle), longitude, latitude, and altitude. The measured wind is transformed to the Earth reference frame from the body-fixed frame using drone-observed wind and positioning angles. The transformed 1-Hz wind data is used to estimate the energy dissipation rate (EDR). The wind-based EDR is estimated by employing two different methods based on second-order structure function and power spectral density (PSD) considering the Kolmogorov’s dependence. First, the second-order structure function is computed for the wind data within predefined inertial range. For the PSD-based EDR, Fast Fourier Transform is applied to the wind data and individual PSD is computed over a 30-second time window and EDR estimate is computed by employing the Kolmogorov-scale slope within predefined inertial range. Relatively large EDRs are observed in the open-space areas besides the river compared to those in the middle of highrise apartment complex, which can be associated with a shadow of wind by the obstacles such as buildings. Detailed analyses on drone-based wind measurements and turbulence will be presented in the conference.

Detection and Analysis of Aircraft Icing Using Dual-polarimetric Radar

Yura KIM#+, Mi-Kyung SUK, MyoungJae SON
Weather Radar Center, Korea, South

Detection of icing is an important of the aircraft operation and icing is a significant hazard to aircraft. When accumulation of ice on the wings of the aircraft and airframe can lead to added weight and drag, loss of lift and thrust, and a serious aircraft accident. Some institutions provided the icing forecast based on numerical models and satellite data, but there is insufficient information that real-time icing observes over the entire Korea Peninsula.
Using 3D radar data and atmospheric information, the Weather Radar Center(WRC) of the Korea Meteorological Administration has developed the algorithm for the icing detection in real time. We consider the atmospheric conditions that the range of temperature and humidity is from -40℃ to 0℃ (Mingione et al., 1997) and 80% or more (Tafferner et al., 2002), respectively. We set the reflectivity(ZH) from 10 to 30 dBZ (Green and Clark, 1972), the differential reflectivity(ZDR) from 0 to 3 dB (Vukits, 2002), and the liquid water content(LWC) from 0.1 to 2.9 g m-3 (William et al., 2011). According to the conditions, we classified into 6 stages and defined the potential areas of icing. It was analyzed and verified that characteristics of icing cases in various environmental conditions such as orographic effect, fronts, stratiform and cumuliform clouds. To verify the developed algorithm, we used the data obtained by an ice detector at aircraft observed by the National Institute of Meteorological Sciences.
In particular, it may allow for safer flights from the risk of icing in low-altitude aircraft such as light aircraft and air ambulance/firefighting helicopter without icing removal devices. The developed algorithm will help decision-making during flight operation by providing the potential areas of icing with real-time over the entire Korean Peninsula that can be observed by radar.

Tue-02 Aug | 10:00 - 11:30 | MR09
AS60 - Atmospheric Rivers: Toward Global Understanding and Applications

Session Chair(s): Agniv SENGUPTA, University of California, San Diego, Bin GUAN, University of California, Los Angeles

AS60-A020 | Invited
Atmospheric Rivers at the Center for Western Weather and Water Extremes: From Science to Solutions

1University of California San Diego, United States, 2Plymouth State University, United States

In response to the unique needs of the Western US, the Center for Western Weather and Water Extremes (CW3E) was established in 2013 at the University of California San Diego Scripps Institution of Oceanography. It provides 21st century water cycle science, education, technology, and outreach to support effective policies and practices addressing the impacts of extreme weather and water events. It strives to revolutionize the physical understanding, observations, predictions, seasonal outlooks, and climate projections of extreme events in western North America, and their impacts on floods, droughts and the economy. CW3E’s development, capabilities, accomplishments, and outlook are summarized with an emphasis on atmospheric river science, and applications to practical problems in water management. CW3E has co-created several Research And Operations Partnerships (RAOP), linking science to solutions. Forecast-Informed Reservoir Operations (FIRO), with the US Army Corps of Engineers and other water partners, demonstrated that atmospheric river (AR) forecasts can increase flexibility in operating some west coast reservoirs, enhancing resilience to changing climate. CW3E championed creation of the AR Program with California’s Department of Water Resources, establishing a rigorous research portfolio supporting FIRO through AR-focused science, predictions, and climate change projections. CW3E co-led creation of AR Recon with NOAA and the Air Force, simultaneously adding unique observations offshore, improving real-time AR forecasts, and conducting science. CW3E has supported a community of experts through education, creating an International Conference, summer Colloquium, the AR Scale, and numerous collaborations. Core values are discovery and practical applications, collaboration, education, diversity, and student and staff growth. CW3E is expanding beyond the West, growing new RAOPs and collaborations, while creating new education opportunities. This presentation will provide a broad overview and context for the development of CW3E, describing how atmospheric rivers flow through its development and are setting the stage for the future.

Historic and Future Atmospheric Rivers and Precipitation in the Middle East and North Africa (MENA)

Elias MASSOUD1#+, Theresa MASSOUD2, Bin GUAN3,4, Agniv SENGUPTA5, Duane WALISER4
1University of California, Berkeley, United States, 2University of Balamand, Dubai, United Arab Emirates, 3University of California, Los Angeles, United States, 4Jet Propulsion Laboratory, California Institute of Technology, United States, 5University of California San Diego, United States

This study investigates the historical climatology and future projected change of atmospheric rivers (ARs) and precipitation for the Middle East and North Africa (MENA) region. We use a suite of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5, historical and RCP8.5 scenarios) and other observations to estimate AR frequency and mean daily precipitation. Despite its arid-to-semi-arid climate, parts of the MENA region experience strong ARs, which contribute a large fraction of the annual precipitation, such as in the mountainous areas of Turkey and Iran. This study shows that by the end of this century, AR frequency is projected to increase (~20–40%) for the North Africa and Mediterranean areas (including any region with higher latitudes than 35 N). However, for these regions, mean daily precipitation (i.e., regardless of the presence of ARs) is projected to decrease (~15–30%). For the rest of the MENA region, including the Arabian Peninsula and the Horn of Africa, minor changes in AR frequency (+/-10%) are expected, yet mean precipitation is projected to increase (~50%) for these regions. Overall, the projected sign of change in AR frequency is opposite to the projected sign of change in mean daily precipitation for most areas within the MENA region.

Influence of Zero-degree Line on Atmospheric Rivers in High Mountain Asia: WRF Case Studies of Orographic Precipitation Extremes

Deanna NASH#+
University of California, Santa Barbara, United States

Atmospheric Rivers (ARs) reach High Mountain Asia (HMA) roughly 10 days per month during the winter and spring, resulting in roughly 20 mm day-1 of precipitation. However, there are a few events each season that result in over 100 mm of precipitation, providing the vast majority of total winter precipitation, indicating that an individual AR event may significantly change water availability within the region in which it occurs. Furthermore, dynamical changes, such as the warming anticyclonic trend in Central Himalaya, have influenced the frequency of ARs and their freezing level height when they reach HMA, impacting the resulting rain to snow ratio and ultimately water resources. Current gridded precipitation products do not have fine enough resolution to resolve the mesoscale processes needed to understand the precipitation patterns during these extreme AR events and improve predictions of moisture availability in this region. To understand the mesoscale processes associated with the orographic precipitation during these extreme events, we intercompare a selection of ARs associated with extreme precipitation during a lowered freezing level and a higher freezing level. The events are dynamically downscaled to 3km spatial resolution using the Weather Research and Forecasting model to resolve the atmospheric flow interactions of ARs with the complex terrain of HMA. This study indicates the importance of exploring dynamical changes in HMA via ARs and the contribution of ARs and the freezing level to orographic precipitation, providing information for future work to improve forecasting skill in a region vulnerable to the impacts of climate change.

Modeling of AR-induced Post-wildfire Debris Flow Susceptibility in California, U.S.A.

Chuxuan LI1#+, Alexander HANDWERGER2, Jiali WANG3, Daniel HORTON1
1Northwestern University, United States, 2NASA Jet Propulsion Laboratory, United States, 3Argonne National Laboratory, United States

Landfalling atmospheric rivers (ARs) can bring intense precipitation that results in extreme hydrological events such as floods, landslides, and debris flows. In the western U.S., intense and widespread wildfires occur in the summer and fall and often precede winter landfalling ARs, which exacerbates the region’s susceptibility to postfire debris flows. In burned areas, decreased rainfall interception by vegetation causes more water to reach the soil and increased soil water repellency decreases infiltration, both of which cause increased surface runoff and hence increased debris flow susceptibility. Despite the hazardous effects of landfalling ARs on burned terrain, debris flow investigations using physics-based numerical models have been limited. Here, we employ a weather radar-derived precipitation product and the Weather Research and Forecasting Hydrological modeling system (WRF-Hydro) to assess regional postfire debris flow susceptibility during a January 2021 AR event that triggered numerous debris flows within a wildfire burn scar in central California. After augmenting WRF-Hydro to account for burn scar characteristics, our simulations show increased flashiness and a multifold increase in total and peak discharge within and downstream of the burn scar, consistent with available streamflow observations. We use catchment-area normalized discharge volume to assess postfire debris flow susceptibility. We find that catchments simulated to have high-to-very high susceptibility correspond well with remotely sensed and field-based debris flow observations. Given the projected upward trends in AR intensity and wildfire season length in California and elsewhere, it is important we continue to develop tools that can predict and assess debris flow susceptibilities, hazards, and risks. Our hindcast application of WRF-Hydro is a promising first step in the development of an operational and physics-based debris flow hazard assessment model for use in regional-scale early warning systems.

Improved Forecast Skill Through the Assimilation of Dropsonde Observations From the Atmospheric River Reconnaissance Program

1University of California San Diego, United States, 2National Oceanic and Atmospheric Administration, United States, 3University of Colorado Boulder, United States

Atmospheric rivers (ARs) are narrow regions through which vast amounts of moisture are transported from tropics/subtropics to mid- to high-latitude regions. Landfalling ARs contribute to up to half of the annual precipitation over the US West, which can both provide beneficial water resources and cause deleterious hazards. Forecasting landfalling ARs is limited by a variety of factors such as poor upstream initial conditions and the degraded quality of satellite radiances under AR conditions. In order to improve forecast skill of ARs and precipitation over the US West, AR Reconnaissance (Recon) program was developed as a research and operations partnership led by the Center for Western Weather and Water Extremes (CW3E) at UC San Diego’s Scripps Institution of Oceanography and National Weather Service (NWS)/National Centers for Environmental Prediction. This study assesses the dropsonde impact on the analyses and forecasts in CW3E’s regional implementation of the Weather Research and Forecasting (WRF) model called West-WRF and the Gridpoint Statistical Interpolation (GSI)-based hybrid four‐dimensional ensemble variational (4DEnVar) data assimilation system. Data denial experiments were performed to evaluate the impact of assimilating AR Recon dropsonde observations collected during 15 Intensive Observation Periods (IOPs) in 2016, 2018, and 2019. Results showed that dropsondes reduced the root-mean-square error in integrated vapor transport (IVT) and inland precipitation for more than 70% of the IOPs, averaged over all forecast lead times. Dropsondes improved the spatial pattern of forecasts of IVT and precipitation in all IOPs. Significant improvements in skill are found beyond 1-2 days. These experiments, together with additional data denial experiments for 2020 IOPs using the GFS system, demonstrated that high-vertical-resolution dropsonde profiles from AR Recon can fill critical observation gaps and improve model analyses, leading to higher forecast accuracy for landfalling ARs.

Subseasonal-to-seasonal Prediction of Wintertime Atmospheric Rivers in the GFDL SPEAR Model

Wei ZHANG1,2#+, Baoqiang XIANG3,2, Kai-Chih TSENG 1,2, Nathaniel JOHNSON2, Lucas HARRIS4, Tom DELWORTH2
1Princeton University, United States, 2NOAA Geophysical Fluid Dynamics Laboratory, United States, 3University Corporation for Atmospheric Research, United States, 4National Oceanic and Atmospheric Administration, United States

Atmospheric rivers (ARs) characterized by intense lower tropospheric plumes of moisture transport are essential to western North America and midlatitude climate. Nevertheless, forecasts of ARs on subseasonal to seasonal (S2S) timescales remain at a low level of skill. Based on hindcast data from the Seamless System for Prediction and Earth System Research (SPEAR) at the Geophysical Fluid Dynamics Laboratory (GFDL), this study aims to evaluate the global forecast skill of wintertime AR activities out to a 4-week lead and examine the sources of S2S predictability using an average predictability time (APT) analysis. We apply an aggregate measure to quantify the prediction skill by counting AR occurrence days within a week-long period (from AR-week1 to AR-week4) and assess the global AR skill through the anomaly correlation coefficient, the root-mean-square error, and the Brier Skill Score. The SPEAR model shows reliable AR forecast skill in the first two weeks and becomes less evident in week 3 in the midlatitudes. Higher forecast skill is detected for strong AR (3-7 days/week) than weak AR (1-2 days/week) activities at 1-4-week lead times, despite that the occurrence probability of weak AR activity outperforms strong AR activities. We further examine the potential sources of predictability based on the APT method and identify three leading modes that can be interpreted as the El Niño–Southern Oscillation, the Pacific North American, and the Arctic Oscillation patterns. Reconstruction of AR forecast skill using the three leading modes suggests comparable results with raw forecast estimation. Moreover, subseasonal AR forecast skill in western North America is modulated by different phases of the Madden–Julian Oscillation and the Quasi-biennial Oscillation, highlighting the window of opportunity for subseasonal AR forecasting.

Tue-02 Aug | 10:00 - 11:30 | MR04
AS21 - Ensemble Modeling of High-impact, Multi-scale Weather to Decadal Phenomena

Session Chair(s): Huiling YUAN, Nanjing University

AS21-A001 | Invited
A Novel Ensemble Forecasting Method for Dealing with Combined Effect of Initial and Model Errors and Its Potential Implementation Using Machine Learning

Wansuo DUAN1#+, Junjie MA1, Stéphane VANNITSEM2
1Chinese Academy of Sciences, China, 2Royal Meteorological Institute of Belgium, Belgium

A new nonlinear forcing singular vector (NFSV) approach is proposed providing optimally combined mode of initial perturbation and model perturbation (C-NFSVs) in ensemble forecasts. The C-NFSVs are optimally growing structure taking into account the impact of the interaction between the initial and model errors effectively, generalizing the original NFSV for simulating impact of model errors. The C-NFSVs is tested in the context of the Lorenz-96 model to show the feasibility in improving ensemble forecast skill. This approach is compared with the orthogonal conditional nonlinear optimal perturbation (O-CNOPs) for estimating initial uncertainties only and the orthogonal NFSVs (O-NFSVs) for estimating model uncertainties only. The results demonstrate that when initial error and model error simultaneously occur in the forecasting system, the C-NFSVs shows much higher ensemble forecasting skill. A deep learning approach is also used to learn the properties of the ensemble members and then overcome the limitation of the expensive cost of the computation of the C-NFSVs and their related ensemble members. The C-NFSVs combined with deep learning approaches could provide a new useful and efficiently ensemble forecasting method for operational forecasting suites dealing with the combined effects of initial and model errors.

Sampling with Ensembles: A Critical Review

Jie FENG#+
Fudan University, China

Forecasts of chaotic systems like the atmosphere become contaminated, then dominated by noise unrelated to the true state of the system. Ensemble forecasting is designed to sample the space of forecast error. At most centers, integrations from perturbed initial conditions have augmented or replaced higher resolution control forecasts started from the best initial condition. Beyond alternative scenarios, ensembles provide a wide range of probabilistic and other products. Random perturbations have a statistically equal projection in each independent phase space direction. Hence in the high dimensional space of atmospheric dynamics, even if statistically indistinguishable from error fields, perturbations have a very small projection on the actual realization of error; the bulk of the variance adds noise in other directions. This results in a cloud of solutions not around, but further displaced from reality. Initial error is doubled, causing a 20-hour drop in forecast skill, equivalent to using NWP output from 8 years ago. This behavior is observed in operational, perfect, and statistically simulated ensembles, suggesting it is not caused by methodological problems. Instead, the failure is due to fundamental limitations in sampling the multidimensional space of atmospheric dynamics. 

The Response of the East Asian Summer Rainfall to More Extreme El Niño Events in Future Climate Scenarios

Sandro F. VEIGA#+, Huiling YUAN
Nanjing University, China

This study investigates what can be the response of East Asian summer rainfall (EASR) if global warming causes more extreme El Niño events in the future. Two multi-model ensembles are built based on CMIP6 models that project stronger El Niño-Southern Oscillation (ENSO) in the future and CMIP6 models that project no changes in ENSO, respectively. Since the ENSO impact in the EASR is influenced by the Pacific Decadal Oscillation (PDO) phase, the analysis separates extreme El Niño events occurring in different PDO phases. During the negative PDO phase, CMIP6 models that project stronger El Niño events also project enhanced EASR anomalies compared with models that project similar El Niño magnitudes to the present. However, during the positive PDO phase, the difference in the magnitude of the EASR changes between the two ensembles is negligible. To understand which components of the ENSO future changes are influencing the EASR changes, an atmospheric moisture budget decomposition is applied. The results indicate that future changes in ENSO-driven wind circulation anomalies are the major contributor to EASR changes.

Tue-02 Aug | 10:00 - 11:30 | MR05
AS11 - The Science and Prediction of Tropical Cyclones

Session Chair(s): Kelvin T. F. CHAN, Sun Yat-sen University, Yuqing WANG, Chinese Academy of Meteorological Sciences

A Time-dependent Analytical Model of Tropical Cyclone Intensification

Yuqing WANG#+
Chinese Academy of Meteorological Sciences, China

In this talk, a time-dependent analytical model of tropical cyclone intensification will be presented. A tropical cyclone (TC) is assumed to be axisymmetric and consists of a well-mixed slab boundary layer and an overlaid free atmosphere in thermal wind balance. The boundary-layer tangential wind and entropy budget equations are used to derive an equation for the tendency of the maximum near-surface wind speed, namely the TC intensification rate (IR). The eyewall updraft in the TC becomes moist neutral in the free atmosphere above the boundary layer as the TC intensifies as recently found based on idealized numerical simulations. Such a tendency is reflected by an ad-hoc parameter, which measures the degree of congruence of the absolute angular momentum (AAM) and the saturated entropy surfaces. The IR equation can be solved analytically with the solutions being supported by results from idealized full-physics numerical simulations and observations. The analytical model indicates a strong dependence of IR on both TC intensity and the corresponding maximum potential intensity (MPI) and also the finite-amplitude nature of TC genesis.

Deep Eye Clouds in Tropical Cyclone Trami (2018) During T-PARCII Dropsonde Observations

Soichiro HIRANO1, Kosuke ITO1#+, Hiroyuki YAMADA1, Satoki TSUJINO2, Kazuhisa TSUBOKI3, Chun-Chieh WU4
1University of the Ryukyus, Japan, 2Meteorological Research Institute, Japan, 3Nagoya University, Japan, 4National Taiwan University, Taiwan

The sporadic formation of short-lived convective clouds in the eye of Tropical Cyclone (TC) Trami (2018) is investigated using dropsonde data and simulation results from a coupled atmosphere–ocean model. According to the satellite data, top height of the convective clouds exceeds 9 km above mean sea level, considerably taller than that of typical hub clouds (2–3 km). These clouds are located 10–30 km away from the TC center. Hence, these convective clouds are called deep eye clouds (DECs) in this study. The dropsonde data reveal increase in relative humidity in the eye region during the formation of DECs. Short-lived convective clouds are simulated up to the middle troposphere in the eye region in the coupled model. Investigation of thermodynamic conditions shows a weakened low-level warm core and associated favorable conditions for convection in the eye region during the formation of DECs. DECs are formed after the weakening and outward displacement of convective heating within the eyewall. To elucidate the influence of the changes in convective heating within the eyewall on the formation of DECs, we calculate secondary circulation and associated adiabatic warming induced by convective heating within the eyewall using the Sawyer–Eliassen equation. In the eye region, weakenings of subsidence and associated vertical potential temperature advection are observed as DECs are formed. This suggests that the weakening and outward displacement of convective heating within the eyewall create favorable conditions for the sporadic formation of DECs.

Structure Changes Preceding Rapid Intensification in Tropical Cyclone Under Moderate Vertical Wind Shear

Chendi WANG1#+, Juan FANG2
1Shanxi Meteorological Observatory; Nanjing University, China, 2Nanjing University, China

Early development of Super Typhoon Lekima (2019) under moderate vertical wind shear (VWS) is examined on the basis of a successfully cloud-resolving simulation with the Weather Research and Forecast model. Lekima evolves from a tilted vortex to an upright vortex with meso-γ-scale vorticity core and finally to a vortex with well-defined eyewall preceding the rapid intensification (RI). The precession of upper-middle-level vortex to the upshear-left is critical to the establishment of an upright vortex with large vorticity concentrated in the center of tropical cyclone (TC). As the upper-middle-level vortex precesses to the upshear-left, horizontal advective effect of VWS weakens TC vortex tilt. In response to the abrupt enhancement of upper-middle-level vorticity, convection occurs in the region closer to TC center. The large vorticity, low stability and high humidity below the upper-middle-level vortex promote the convection, causing the formation of intense meso-γ-scale vortex that becomes vorticity core of the well-aligned TC vortex. This process is quite similar to the downshear reformation paradigm except that the compelling meso-γ-scale vortex develops primarily in the upshear-left. RI does not commence right after Lekima becomes an upright vortex. Instead, it occurs when the distinct eyewall, characterized by convection and vorticity rings, develops in the aligned TC vortex. The latent heating released from convection near the center and the advection of warm air from convection region at a distance both contribute to the eyewall formation via strengthening the warm core. The unbalanced boundary-layer process emphasized in secondary eyewall formation also contributes to the primary eyewall formation in Lekima. The structure changes preceding RI mentioned above are not the only way in which the TC responds to moderate VWS. The sensitivity experiments show that Lekima evolves directly from a tilted vortex to an upright vortex with well-defined eyewall preceding the RI when the sea-surface temperature is higher.

Examining the Eyewall Replacement Cycle of Typhoon Lekima (2019) Using Forward and Backward Trajectory Analyses

Shang-En LI#+, Ming-Jen YANG
National Taiwan University, Taiwan

In this study, the eyewall replacement cycle (ERC) of Tropical Cyclone (TC) Lekima (2019) are examined by using forward- and backward-trajectory analyses. Observation by radars at Mount Wufen and Ishigaki Island showed that the double eyewall structure of TC Lekima maintained over 36 hours. The inner eyewall started to dissipate after the construction of outer eyewall due to the lack of low-level moisture supply from an axisymmetric view. Physical mechanism for the maintenance of the long-lived ERC will be examined by forward- and backward-trajectory analyses. TC Lekima was simulated by the full-physics WRF model nesting down to 1-km horizontal grid spacing, and then the forward- and backward-trajectory analyses were performed using the simulated high-resolution three-dimensional wind field. Results of the forward trajectory analysis showed that about 40 percent of air parcels were trapped in the moat region (the region between inner and outer eyewalls) if the air parcels were released at low-to-middle levels (1–6 km) in the moat region 12 hours before the ERC. Over 80 percent of air parcels were trapped in the moat region if parcels were released at middle levels (2–8 km) at the time when the outer eyewall was apparent (the mature stage of ERC). About 20 to 40 percent of air parcels were trapped in the moat region if parcels were released inside the boundary layer (below 1 km) at the moat and outer eyewall regions during the entire period of ERC.

Analysis of Typhoon Eye Diameters in Satellite Images

Namiko TORIYAMA1#+, Tsubasa KOHYAMA1, Hiroaki MIURA2
1Ochanomizu University, Japan, 2The University of Tokyo, Japan

The existence of the eye of a typhoon is well known that determines thought its features are still burgely unexplored. In particular, the mechanism that determines a typhoon eye. The analysis of typhoon eyes leads to a deeper understanding of the physical structure of typhoons, which in turn improves the reliability of typhoon track and intensity forecasts. In this study, we develop an algorithm that automatically analyzes high-resolution satellite images and creates a dataset of typhoon eye diameters. This dataset is prepared as follows. First, we access the website “Digital Typhoon”, which is operationally updated by the National Institute of Informatics in Japan. Next, the satellite image at the time of the lowest central pressure is downloaded. From the center of the typhoon, pixels without cumulonimbus are searched recursively. After examining all adjacent pixels without cumulonimbus, the “equivalent diameter” of the eye is calculated based on the information of the total number of adjacent pixels without cumulonimbus. The aforementioned method yields a dataset that contains the data of 336 typhoon eyes from 1979 through 2019. The mean typhoon eye diameter is approximately 40 km from 10°N to 35°N, but the eyes tend to be slightly larger in higher latitudes, which is consistent with a previous study before the satellite era. The annual mean time series of the typhoon eye diameters show that the typhoon eyes have gradually expanded for the past 40 years.

On the Two Types of Tropical Cyclone Eye Formation: Clearing Formation and Banding Formation

Yueh-Li CHEN#+, Chun-Chieh WU
National Taiwan University, Taiwan

Two types of eye formation are proposed: “clearing formation (CF)” and “banding formation (BF)”. The objectives are to identify the tropical cyclone (TC) characteristics associated with these two types of eye formation and to clarify how the environment, pattern of synoptic systems and TC structure during initial and development stages affect the eye formation. The satellite imagery and best-track data are used to classify and analyze the TCs named in the western North Pacific from 2007 to 2020. The results show that TCs with CF have significantly higher intensity and intensification rate during the period of the first eye presence, smaller size after genesis and prior to eye formation, smaller eye size when the eye forms and a more westward track. It is noted that CF and BF TCs tend to occur in autumn and summer, respectively. Meanwhile, the composite results using reanalysis data show that the CF TCs are generally characterized by easterly-wave features with a dryer environment, smaller initial size and larger radial gradient of vorticity, while the BF TCs feature a monsoon-depression structure with a wetter environment, larger initial size and flatter vorticity profile. A conceptual hypothesis is thus proposed, as compared to BF TCs, the smaller size and weaker outer wind in CF storms associated with the easterly-wave disturbance are facilitated by inactive outer convection, leading to larger radial gradient of inertial stability. The low-level inflow can penetrate inward close to the center, resulting in more diabatic heating inside the radius of maximum wind with much higher heating efficiency, and also a higher intensification rate.

Tue-02 Aug | 10:00 - 11:30 | MR06
AS28 - Global Precipitation Measurement, Science, and Applications

Session Chair(s): Yukari TAKAYABU, The University of Tokyo, Geun-Hyeok RYU, Korea Meteorological Administration

AS28-A004 | Invited
Diurnal Cycles of Precipitation and Lightning in the Tropics Observed by TRMM3G68, GSMaP, LIS, and WWLLN

Shoshiro MINOBE1#+, Jun Hyock PARK1, Katrina VIRTS2
1Hokkaido University, Japan, 2The University of Alabama in Huntsville, United States

Diurnal cycles of precipitation and lightning are investigated by analyzing rain rates of the TRMM3G68 dataset, consisting of Precipitation Radar and Microwave Imager data only; rain rates of Global Satellite Mapping of Precipitation (GSMaP), for which infrared (IR) data are also used; lightning flash rates observed by TRMM Lightning Imaging Sensor (LIS); and lightning stroke rates of World Wide Lightning Location Network (WWLLN) over the tropics. Diurnal amplitudes relative to averages are generally larger for lightning than for precipitation. Over ocean, relative amplitudes are stronger in the stratocumulus deck region in the southeast Pacific than those over typical ocean regions. The phase of GSMaP is substantially delayed to TRMM3G68 due to the phase-delay problem of IR-based estimation. The diurnal peaks tend to occur between 1400 and 1800 LST over the continent after spatial averaging with a phase leading order of TRMM3G68, LIS, and WWLLN, and between 0000 and 0700 LST over oceanic regions where diurnal cycles are prominent in all datasets. Off-equatorward phase propagations are found in the precipitation in the Pacific and Indian Oceans. Over selected coastal regions, all data exhibit consistent oceanward phase propagation with the longest, medium, and shortest phase propagation distances for TRMM3G68 precipitation, WWLLN lightning, and LIS lightning, respectively, with a phase leading order of LIS, WWLLN, and TRMM3G68. The summertime diurnal cycle over the Gulf Stream also exhibits oceanward phase propagation, but with strong amplitude enhancement over the Gulf Stream. Diurnal cycle amplitude is also enhanced over the Kuroshio in the East China Sea in the baiu–mei-yu rainy season.

Evaluation and Application of Satellite Precipitation Products in Studying the Various Types of Rainfall Events in Taiwan

Wan-Ru HUANG#+, Pin-Yi LIU, Ya-Hui CHANG, Cheng-An LEE, Jie HSU
National Taiwan Normal University, Taiwan

This talk presents our recent works on the evaluation of various satellite precipitation products (SPPs) in studying the warm season rainfall in Taiwan, with a focus on the potential application in studying two important rainfall events: convective afternoon rainfall (CAR) and typhoon (TC). In the first part of the talk, we evaluate the four post-real-time SPPs (including TRMM-3B42 v7, IMERG-F v5, IMERG-F v6, and GSMaP v7) in studying summer CAR events. Our analyses show that when using more than 400 rain-gauge observations in Taiwan as a reference base for comparison, IMERG-F v6 outperforms others quantitatively and qualitatively, more accurately depicting the variations of the summer rainfall at multiple timescales (including mean status, daily, and diurnal). IMERG-F v6 also performs better than others in capturing the characteristics of CAR activities. Therefore, in the second part of talk, we further focus on the evaluation and application of the post-real-time and near-real-time products of IMERG v6 in depicting the characteristics of TC season (July to October) rainfall. Our results show that all IMERG products (including IMERG-E, IMERG-L, and IMERG-F) capture the spatio-temporal variations of TC rainfall better than those of non-TC rainfall. The IMERG-F performs better than the IMERG-L, which is slightly better than the IMERG-E for most of the features assessed for both TC and non-TC rainfall. Despite these differences, all IMERG products outperform the frequently used TRMM-3B42 v7 for the illustration of the spatio-temporal characteristics of TC rainfall. In contrast, for the non-TC rainfall, the IMERG-F performs notably better relative to TRMM-3B42 v7, while the IMERG-E and IMERG-L showed only slight improvement. Finally, we show the evaluation of near-real-time products for GSMaP v6 and v7 in studying the warm season extreme rainfall in Taiwan. We find that GSMaP-Gauge-NRT is better than GSMaP-NRT in depicting the extreme rainfall events.

Performance Assessment of GPM-based Near-real-time Satellite Products in Depicting Diurnal Precipitation Variation Over Taiwan

Jie HSU+, Wan-Ru HUANG#, Pin-Yi LIU
National Taiwan Normal University, Taiwan

This study evaluated the performance of four near-real-time (NRT) multiple-satellite precipitation products (MSPPs) from the Global Precipitation Measurement (GPM) mission in depicting the variation in diurnal precipitation from 2017 to 2020, in May to September (MJJAS). The four NRT MSPPs include the V06 of Integrated Multi-satellitE Retrievals for the GPM Early Run (IMERG-E) and Late Run (IMERG-L), and the V07 of Global Satellite Mapping of Precipitation NRT (GSMaP-N) and Gauge-NRT (GSMaP-GN). Two sub-components of diurnal precipitation variation were evaluated, daily mean (Pm) and anomalies (ΔP); ΔP was further separated into diurnal (S1) and semidiurnal (S2) harmonic modes. Compared with surface observations, results show that all NRT MSPPs underestimate Pm and ΔP, but IMERG products are better than GSMaP products in most of the examined spatial characteristics. Temporally, only IMERG-E depicts the phase evolution of both S1 and S2, similar to surface observations. These findings indicate that IMERG-E is the best NRT product for studying the diurnal precipitation characteristics across MJJAS in Taiwan. The general bias in the NRT MSPPs considered in the study in depicting the features examined was attributed to the limitation of passive microwave sensors in illustrating the developing and dissipating stage of diurnal precipitation formation, and to the weakness of infrared precipitation algorithms in detecting warm orographic clouds.

Reexamination of Precipitation Type Classification for Spaceborne Radars Using a Ground Based Doppler Radar Over the Tibetan Plateau

Takeshi MASAKI1#+, Shoichi SHIGE1, Hiroyuki YAMADA2
1Kyoto University, Japan, 2University of the Ryukyus, Japan

Vertical air motion should be used for determining the type of precipitation, but radar reflectivity is used as a proxy parameter for precipitation type classification of TRMM Precipitation Radar (PR) and GPM Dual-frequency Precipitation Radar (DPR) because that they are not able to observe the vertical air motion directly. This restriction leads to misclassification of the classification especially over Tibetan Plateau in summer season. We examined the classification estimated by TRMM PR using NASDA X-band doppler radar observation on Tibetan Plateau in the GAME-Tibet project. On 22:43LT August 1, 1998, when the NASDA doppler radar and PR observed same precipitation system simultaneously, the PR mostly classified precipitation system into stratiform precipitation, whereas the vertical profile of the horizontal wind divergence revealed by Velocity Azimuth Display (VAD) method indicates divergence profiles associated mainly with convective precipitation. This misclassification may be caused by the threshold (40 dBZ) for classifying convective precipitation in the PR's precipitation type classification algorithm was obtained over the tropical ocean and does not sufficiently take into account regional characteristics over the Tibetan Plateau. Shimizu et al.(2001) has concluded that there was no convective precipitation on August 1, however, we revealed that low-level wind convergence evolved into middle-level convergence, implying the convective-stratiform evolution. It is most likely caused by using multiple elevation angle observations instead of a single elevation angle.

AS28-A014 | Invited
Comparison of GPM DPR Products Related to Ice-phase Precipitation

Kenji SUZUKI1#+, Rimpei KAMAMOTO2
1Yamaguchi University, Japan, 2Railway Technical Research Institute, Japan

The Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM) core satellite gives us useful products such as flagHeavyIcePrecip and flagGraupelHail, which indicate microphysical structures in clouds. The flagHeavyIcePrecip shows active ice formation above -10 degrees Celsius altitude, while the flagGraupelHail shows the existence of graupel of hail in a cloud. These two products detect solid precipitation with different algorithms. In this study, we compared these two products in rain/snow events observed by DPR around Japan from May 2018 to August 2021, focusing on the lightning activity, seasonal variation, microphysical features in clouds. These two products generally detect solid precipitation particles formed in convective regions, and these solid precipitation particles are well known to be related to lightning occurrence. According to the analysis of past heavy rainfall cases, their distribution was in good agreement with the lightning distribution in the convective region, but the detection frequency of these two products was different, and it was confirmed that flagGraupelHail was detected even in the stratiform region where there was no lightning. In addition, flagGraupelHail was rarely detected in winter. When both products were detected simultaneously during the warm season, the average zfactor was larger than when each product was detected alone. In terms of precipitation type, flagHeavyIcePrecip was detected relatively frequently in the convective region, while flagGraupelHail was detected in the stratiform region in many cases. As a result of comparing the two-dimensional frequency distributions of radar reflection intensity and temperature for stratiform and convective, respectively, the radar reflectivity in the cases of flagGraupelHail had no significant difference between stratiform and convective regions above 0°C altitude, indicating that solid precipitation formation were more active than non-flagGraupelHail case. This feature was more pronounced in cases that brought heavy rainfall.

Analysis of a Precipitation System Causing Heavy Rainfall Over Kyushu in August 2021 Using GPM KuPR Observation Data

Hiroki TSUJI#+, Yukari TAKAYABU
The University of Tokyo, Japan

Characteristics of a precipitation system developed during a heavy rainfall over Kyushu, Japan in August 2021 are analyzed using observation data from the Ku-band precipitation radar (KuPR) onboard the Global Precipitation Measurements (GPM) core observatory and the initial values of the Japan Meteorological Agency Mesoscale model (MSM). We found from analyses with the MSM data that free-tropospheric water vapor flux convergence increased about one day before the development of the precipitation system observed by GPM and contributed to moistening atmosphere. In contrast, boundary-layer water vapor flux convergence showed a small contribution to the development of the precipitation system. A moist absolutely unstable layer (MAUL) was analyzed around an ascending region of a deep inflow layer in the precipitation system. MAUL is an absolutely unstable layer that results from a convectively unstable layer lifted by mesoscale circulation associated with organized mesoscale convective systems. A mesoscale precipitating area covering the Kyushu Island was observed by KuPR. Intense convective precipitation over 40 mm h-1 was observed around the area where MAUL was analyzed. However, the other areas in the observed precipitation system consisted of weak (less than 20 mm h-1) stratiform precipitation with clear bright bands. Precipitation top heights less than 12 km and maximum 40 dBZ echo top height of 7km were observed in the precipitation system. These characteristics are consistent with precipitation systems organized with mesoscale circulation observed over the tropical oceans and different from tall convections like thunderstorms. These results indicate that the precipitation system observed during the August 2021 rainfall event had characteristics of organized precipitation systems with mesoscale circulation.

Tue-02 Aug | 10:00 - 11:30 | MR03
AS35 - Idealised Frameworks, Modelling, and Observations to Understand Moist Convective Processes at Various Scales

Session Chair(s): Maxime COLIN, Leibniz Centre for Tropical Marine Research, Chien-Ming WU, National Taiwan University, Ji NIE, Peking University, Yi-Ling HWONG, Institute of Science and Technology Austria (ISTA)

AS35-A004 | Invited
A Shallow-water Model for Convective Self-aggregation

University of California, Davis, United States

Randomly distributed convective storms can self-aggregate in the absence of large-scale forcings. Here we present a 1D shallow-water model to study the convective self-aggregation. This model simulates the dynamics of the planetary boundary layer and represents convection as a triggered process. Once triggered, convection lasts for finite time and occupies finite length. We show that the model can successfully simulate self-aggregation, and that the results are robust to a wide range of parameter values. In the simulations, convection excites gravity waves. The gravity waves then form a standing wave pattern, separating the domain into convectively active and inactive regions. We analyze the available potential energy (APE) budget and show that convection generates APE, providing energy for self-aggregation. By performing dimensional analysis, we develop a scaling theory for the size of convective aggregation, which is set by the gravity wave speed, damping time scale, and number density of convective storms. This study provides a simple modeling framework to further study spontaneous organization of convective storms. 

Idealized Simulation of Convectively Coupled Kelvin Wave Using the Single-column Unified Forecast System

I-Kuan HU1#+, Stefan TULICH2, George KILADIS2, Juliana DIAS2
1Cooperative Institute for Research in Environmental Sciences, United States, 2National Oceanic and Atmospheric Administration, United States

In hoping to better understand and correct the sources of error in the simulations of convectively coupled equatorial Kelvin waves (CCEKWs) in NOAA’s Unified Forecast System (UFS), this study utilizes an idealized framework where the single column UFS (executed as the Common Community Physics Package single column model) is coupled to large-scale vertical velocity parameterized using the damped gravity wave method. Specifically, we focus on the physics suites of the Global Forecast System (GFS) version 16 (v16), and compare the simulations of GFSv16 to that of a cloud resolving model named System for Atmospheric Modeling (SAM) in a limited domain. The coupled system of each model is linearized against its own radiative-convective equilibrium (RCE). The results show that, when comparing to the simulation of SAM (which is taken as a benchmark), the GFSv16 produces bottom-heavier vertical structures, yet faster phase speed, of CCEKWs. We hypothesize the discrepancies between the GFSv16 and SAM can primarily be attributed to differences in their basic states (i.e. their RCEs). Particularly, the planetary boundary layer and lower troposphere of the GFSv16 RCE are drier than that of the SAM RCE. The low-level moisture deficit tends to disfavor the development of deep convection and thus the stratiform component of the convectively coupled system, resulting in bottom-heavier vertical structures of the simulated CCEKWs in the GFSv16. As a step toward improving the simulated basic state and CCEKWs in the UFS, the potentially influential factors of a cumulus convection scheme, such as treatments of downdraft and evaporation of rain, triggering function, and algorithms of entrainment and detrainment are explored.

Convective Response in a Cloud-permitting Simulation of the MJO: Time Scales and Processes

Yan LIU1#+, Zhe-Min TAN1, Zhaohua WU2
1Nanjing University, China, 2Florida State University, United States

Convective response under multi-scale forcing is investigated in this study using a month-long cloud-permitting simulation of the MJO. Convective response time scale (τ) is defined as the time lag between moisture convergence and convective heating. Results imply that τ is dependent on spatial and temporal scales of convective systems. Particularly, estimated τ for slowly varying signals (periods above 2.0 days) on the microscale and synoptic scale is about zero and 0.5 day, corresponding to instantaneous and non-instantaneous response respectively. There are two main phases related to the processes of convective response: shallow convection development and shallow-to-deep convection transition. They are controlled by synoptic-scale boundary layer moisture convergence (M) and lower-tropospheric specific humidity (qm). In the first phase, as qm is small and lags the development of shallow convection, shallow convection occurrence is solely dominated by M (given suitable thermodynamic conditions in the boundary layer). In the second phase, shallow convection further preconditions the atmosphere for shallow-to-deep convection transition by increasing M and qm through convection-convergence non-instantaneous feedback, i.e., shallow convection drives large-scale circulation that enhances moisture convergence and upward moisture transport. Additionally, eddy moisture upward transport by shallow convection itself (convection-convergence instantaneous feedback) also contributes to increase of qm. Comparison of the initiation and propagation stages of MJO indicates that τ is shorter in the propagation stage since M and qm are larger therein. 

Seasonal RCE on Moisture Space From the Observational Perspectives

Peng-Jen CHEN#+, Wei Ting CHEN, Yen-Ting HWANG, Chien-Ming WU
National Taiwan University, Taiwan

Radiative convective equilibrium (RCE) is the balance between the net radiative effect and the heating effect by the latent and sensible heat fluxes. RCE is often applied to constrain the atmospheric energetics on a global scale as well as in the idealized simulations of convection aggregation. However, it remains challenging to identify the appropriate temporal and spatial scales to associate the observed RCE and its relationship to convection structure to those in the modeling studies. This work investigates the observed characteristics of seasonally achieved RCE state over a limited (20o-lat-by-60o-lon) region over the mid-Pacific Ocean. The target region exhibits a sharp temporal transition of energy balance from a energy loss state before summer to a near-balance state in the late summer with a clear west-to-east dry static energy (DSE) transport within the region. We then define the pre-RCE and RCE periods, each with a duration of 12 pentads, to derive and contrast the statistics of convective cloud from CloudSat and precipitation object from TRMM on the moisture space. During RCE, the upward mass flux becomes substantial and the cloud frequency (CF) increases 15% from mid- to high-levels (500hPa~200hPa) over the moist condition (CWV>40 mm), while over the dry condition (CWV<30 mm) the downward mass flux also becomes stronger with the top-heavy structure, and the CF drop 5% to 15% at all altitudes, relative to the pre-RCE period. The longwave cloud radiative effect shows a similar change as the CF. The precipitation object of all sizes tends to be suppressed over dry conditions in RCE, while only the occurrence of the large-size (>300 km) objects increases over the moist condition. We also found that nearly 15% of the large-size objects are associated with the tropical cyclones during RCE, while the ratio drops to 1.5% during the pre-RCE period.

Factors Controlling Precipitation Intensity in Idealised Monsoon Simulations Over an Aquapatch

Maxime COLIN1#+, Jan O. HAERTER1, Vishal DIXIT2
1Leibniz Centre for Tropical Marine Research, Germany, 2TU Delft, Netherlands

The traditional view of monsoons as continental sea breezes generated by land-sea contrasts was shown to have serious limitations. Therefore, it remains unclear (1) if the surface temperature contrast matters for the monsoon precipitation, and (2) why there is a non-linear intensification of precipitation intensity with surface temperature gradients. Here, we aim to determine if monsoon non-linearities with surface forcing come from convective processes, dynamical feedbacks, or from non-linearities in the forcing themselves. Idealised studies such as aquaplanets often help improve our understanding of basic mechanisms. But there are very few idealised simulation studies of monsoons at high resolution. So we devise a modular framework to simulate idealised monsoons at convection-permitting resolution with the WRF model, in a domain based on an aquapatch (rectangular mini-aquaplanet), but in which we can gradually add more realistic components, such as an interactive land surface. The model is forced by a meridional contrast of surface temperature, with comprehensive physics, rotation, and symmetric boundary conditions at the North and South boundaries. In particular, we analyse a series of aquapatch experiments with different Sea Surface Temperature (SST) gradients, different SST peak locations, with and without rotation, and for different types of boundary conditions. Preliminary results show various ITCZ migration behaviours depending on simulation parameters. Some simulations manage to capture the subtropical Westerly jets and the Hadley cell, others don’t. Many simulations have reduced convection at the Equator.

Tue-02 Aug | 10:00 - 11:30 | MR02
AS25 - Dynamics and Prediction of Multi-scale Climate Variabilities Over Asia-pacific Region

Session Chair(s): Bo WU, Institute of Atmospheric Physics, Chinese Academy of Sciences, Lu WANG, Nanjing University of Information Science & Technology

AS25-A020 | Invited
A Multivariate Index for Tropical Intraseasonal Oscillations Based on the Seasonally-varying Modal Structures

Shuguang WANG#+
Nanjing University, China

The spatial structure and propagation characteristics of tropical intraseasonal oscillations vary substantially by season. In this study, these seasonal variations are identified using a multivariate sliding-window Empirical Orthogonal Function (EOF) analysis. The two modes comprising the leading EOF pair have equal variances and depict the propagation of intraseasonal oscillations in convection and low-level circulation over the Indian Ocean, the Maritime Continent, and the western Pacific region in the equatorial summer hemisphere. In contrast, the upper tropospheric circulation shows more structure in the winter hemisphere. It is suggested that this variation in seasonality with height is an inherent feature of intraseasonal oscillations. A new multivariate index for tropical intraseasonal oscillations (MII) is developed based on the leading EOFs and represents the three-dimensional structure of intraseasonal variability in all seasons. The MII is computed by projecting intraseasonal anomalies onto the leading EOFs pair, and it exhibits clearly delineated but smooth seasonal transitions and rich meridional structure. The real-time version of this new index, rMII, is shown to be similar to MII, with a correlation of 0.9. Compared to the widely used Real-time Multivariate MJO (RMM) index, the power spectrum of rMII represents substantially greater intraseasonal variance, and the application of rMII in dynamical forecast models indicates rMII is skillfully predicted for an additional week compared to RMM.  (Reference:  Wang, S., Martin, Z. K., Sobel, A. H., Tippett, M. K., Dias, J., Kiladis, G. N., Ren, H-L, Wu, J. (2022). A Multivariate Index for Tropical intraseasonal Oscillations based on the Seasonally-varying Modal Structures. JGR-Atmospheres, 127,e2021JD035961.https://doi.org/10.1029/2021JD035961.)

Dependence of the MJO Prediction Skill on MJO Diversity

Xuan ZHOU+, Lu WANG#
Nanjing University of Information Science & Technology, China

The MJO is one of the predictability sources in S2S forecasting. In this study, we explore the relationship between the overall and individual prediction skills based on the 15-yr reforecast of the ECMWF and CMA operational forecasting systems, then compare the key differences among predicted high-skill, middle-skill and low-skill MJO events. It is found that the model exhibiting relatively higher MJO overall prediction skill tends to have more cases with higher prediction skill and less cases with lower prediction skill, and vice versa. The high-skill MJO events are characterized by systematic eastward propagation from the Indian Ocean to the central Pacific Ocean, with the a speed of about 5m/s. The middle-skill events are similar to the high-skill ones, except for shorter propagation, which end over the western Pacific (WP). The low-skill MJO events fade before across the Maritime Continent, resembling the standing oscillation mode proposed by Wang et al. (2019). The initial convection anomalies of the high- and middle- skill MJO events show a dipole structure with enhanced convection anomaly over the eastern Indian Ocean (EIO) and suppressed convection anomaly over the WP, but the high-skill events show stronger amplitude. The low-skill MJO events only exhibit a monopole structure of enhanced convection anomaly over the EIO. There is significant linear relationship between prediction skill for individual MJO event and initial convection anomalies over the EIO and WP. The consistence and difference of our result and previous studies are discussed. These findings may help to improve the MJO prediction in current dynamic models.

Diversity of MJO Initiation Regions and Processes

Tianyi WANG#+, Tim LI
University of Hawaii, United States

The diversity of the Madden-Julian Oscillation (MJO) initiation regions was explored using a clustering method. Regions favorable for MJO initiations are grouped into four longitude zones, the Atlantic and Africa (AA), the Indian Ocean (IO), the Maritime Continent (MC), and the western Pacific (WP).
The initiation mechanism is region-dependent. The AA initiation is attributed to a circumnavigating process associated with a preceding MJO. As upper-tropospheric westerly anomalies move into the AA region, the associated descending motion leads to suppressed convection over the IO, which further triggers convection onset to its west through anomalous westward moisture advection. The IO initiation arises from the downstream forcing of a preceding suppressed phase of MJO. In addition, a delayed air-sea interaction process also plays a role. The MC initiation is triggered by a westward-propagating equatorial Rossby wave in the Pacific. The low-level poleward flows associated with the anti-cyclonic Rossby wave gyres advect high mean moisture, promoting the convection onset over the MC. The WP initiation is triggered by a preceding suppressed phase of MJO that moves eastward, in a way similar to the downstream scenario in the IO.
The AA initiation is usually associated with a La Niña-like background. The cold sea surface favors the decoupling of upper-tropospheric westerly anomalies from the preceding MJO, and also inhibits local enhancement of the associated descending motion until it arrives at the IO. The MC and WP initiations are more frequent during El Niño as the mean moisture has a sharper meridional gradient over the central Pacific and is higher over the eastern Pacific, both favoring positive anomalous advections to the initiation regions by the intraseasonal flows.

Reexamining the Moisture Mode Theories of the Madden-Julian Oscillation Based on Observational Analyses

Feng HU1#+, Tim LI2, Jianyun GAO3, Lisheng HAO4
1Chuzhou University, China, 2University of Hawaii, United States, 3Fujian Climate Center, China, 4Tianjin Climate Center, China

Two existing moisture mode theories of the MJO, one emphasizing boundary-layer moisture asymmetry (MA) and the other emphasizing column-integrated moist static energy (MSE) tendency asymmetry (TA), were validated with the diagnosis of observational data during 1979-2012. Total 2343 MJO days are selected. While all these days show a clear phase leading of the boundary-layer moisture, 20% of these days do not show a positive column-integrated MSE tendency in front of MJO convection (non-TA). A further MSE budget analysis indicates that the difference between the non-TA composite and the TA composite lies on the zonal extent of anomalously vertical overturning circulation in front of the MJO convection. A background mean precipitation modulation mechanism is proposed to explain the distinctive circulation responses. Dependent on the MJO location, an anomalous Gill response to the heating is greatly modulated by the seasonal mean and ENSO induced precipitation fields. Despite of a negative MSE tendency in front of MJO convection in the non-TA group, the system continues moving eastward due to the effect of the boundary-layer moistening, which promotes a convectively unstable stratification ahead of MJO convection. The analysis result suggests that the first type of moisture mode theories, the moisture asymmetry mechanism, appears more robust, particularly over the eastern Maritime Continent and western Pacific.

The Role of Multiscale Interaction in the Maintenance and Propagation of MJO

Jiwang MA1+, X. San LIANG2#
1Shandong Meterological Observatory, China, 2Fudan University, China

The multiscale interaction and its role in the lifecycle of the Madden-Julian Oscillation (MJO) has been investigated using the newly developed multiscale window transform (MWT), the theory of canonical transfer, and the MWT-based multiscale energetics analysis. The field variables are reconstructed/filtered with MWT onto three scale windows, namely, high-frequency window (shorter than 32 days), intraseasonal scale window (32-128 days) and low-frequency window (longer than 128 days). Compositing the intraseasonal fields with respect to the real-time multivariate MJO (RMM) index unambiguously shows that an MJO lifecycle is made of two distinct states, a local state and a global state. In the local state, MJO is energized by pressure work and buoyancy conversion, consistent with previous studies. The new findings are that MJO is also energized by the canonical kinetic energy (KE) transfer from the low-frequency window to the intraseasonal window (signifying barotropic instability) on the west of its convection. But on the eastern side, MJO loses KE to the low-frequency window. The KE may also be transported away. In the global state, the MJO variabilities can be characterized by two modes---the Eastern Hemisphere mode and the Western Hemisphere mode. The former is essentially the same as its local counterpart; for the latter, barotropic instability dominates. On the available potential energy (APE) budget, baroclinic instability and intraseasonal APE transport account for producing and maintaining the temperature anomalies. 

Tue-02 Aug | 12:00 - 13:30 | MR01
AS08 - Future of Cities within the Context of Climate Change

Session Chair(s): Jiachuan YANG, The Hong Kong University of Science and Technology

Effects of Urbanization on Heat Stress Under Relatively Dry and Wet Warm Conditions in a Semiarid Urban Environment

Arizona State University, United States

This research examines the role of urbanization on heat stress intensity (HSI) and wet bulb globe temperature (WBGT) (Guyer et al., 2021; Sarangi et al., 2021) for the two largest urban agglomerations in Arizona (AZ), the Phoenix and Tucson metropolitan areas, using the WRF model. We simulate meteorological conditions during relatively dry and wet summer (JJA) periods at high spatial resolution. The selected three-month periods represent the driest and wettest summers from a 15-year contemporary period (2007-2021) based on the CPC UGB Analysis of daily accumulated precipitation over AZ. Urbanization impacts are assessed by performing two identical WRF experiments for each summer with different land use-land cover (LULC) representations: one WRF simulation with the current urban LULC (WRF_URB) and one WRF simulation (WRF_NOURB) using a replacement of all urban grid cells with the dominant regional land cover type. Contemporary urban LULC is characterized by using the USGS 30-m 2019 NLCD (Wickham et al. 2021), which recognizes four urban categories based on the concentration of buildings (i.e., developed open space areas, low intensity areas, medium intensity areas, and high intensity areas) and the fraction of impervious surfaces. These four urban classes are subsequently grouped into three urban categories: low-intensity residential (LIR), high-intensity residential (HIR), and commercial or industrial areas (COI). The Noah LSM (Chen and Dudhia, 2001) and the multilayer building energy model (MBEM; Salamanca et al. 2011) coupled to WRF provide the lower boundary conditions from the natural and urban surfaces, respectively. The urbanization impacts on HSI and WBGT are estimated from the difference between WRF_URB and WRF_NOURB simulations. Our analysis extends to a quantification of the number of heat caution hours (i.e., number of hours in a day that HSI and WBGT exceed a particular threshold) that ensue as a result of the presence of urban surfaces.

Spatiotemporal Impact of Vehicle Heat on Urban Thermal Environment and the Potential Benefit of Electric Vehicles

Xuan CHEN1+, Jiachuan YANG1#, Rui ZHU2, Wong MAN SING2, Chao REN3
1The Hong Kong University of Science and Technology, Hong Kong SAR, 2The Hong Kong Polytechnic University, Hong Kong SAR, 3The University of Hong Kong, Hong Kong SAR

Vehicle heat (VH) is a substantial portion of anthropogenic heat and can affect the urban thermal environment. Under the stimulus of carbon neutrality, the global electric vehicle (EV) market has increased from 0.3 million in 2012 to more than 11 million in 2020. Potential environmental benefits of EVs include enhanced pedestrian thermal comfort, reduced building cooling demand, improved air quality, etc. In addition, the shift to electric vehicles allows the advance of automated driving and vehicle sharing systems, which can further benefit the urban environment if saved parking spaces are to be converted to green infrastructure. Quantifying the impact of VH is essential to assess the potential benefits of EVs in cities, yet the spatiotemporal impact of VH has not been investigated separately. This study incorporates VH and urban landscape data into the Weather Research and Forecasting (WRF) model to estimate the VH impacts in 2015 and 2050 at a fine spatial resolution over Hong Kong. Results show that the temperature change due to the current VH is larger in winter than in summer. Increased air temperature over the urban area by VH correlates with urban area fraction and building height positively. The warming effect would be strengthened 20% under one of the worst global warming scenarios (ssp585) in 2050 compared to the current, especially during the evening rush hours. By promoting the local green transportation policies, EV and consequently reduced parking areas can enhance the urban thermal environment. The study provides insights into the potential benefits of green transportation technology and human-environment interactions along with the development of cities.

Impact of Urbanization to the Future Thermal Environment of Worldwide Megacities

Do Ngoc KHANH#+, Alvin Christopher Galang VARQUEZ, Manabu KANDA
Tokyo Institute of Technology, Japan

The rising temperature of cities is caused by global climate change and urban heat island effect. General circulation models are often used to project global future climate; however, they cannot consider the highly heterogeneous urban surface. On the other hand, regional climate models can investigate urban climate in detail but past studies mainly targeted one or few cities of interest instead of targeting worldwide cities at once. In this study, we project the future climate under the worst case scenario for 43 megacities, taking both global warming and urbanization into account. Global warming is considered by downscaling global projection using the pseudo-global warming method. Urbanization is considered by changing urban morphological parameters and anthropogenic heat based on projections of population and GDP. The heterogeneity of the urban surface is expressed by 1 km resolution urban morphological parameters and anthropogenic heat maps. We found that the distribution of temperature change between the 2010s and the 2050s differs significantly between the projection considering urbanization and the projection not considering urbanization. The average warming due to urbanization of the 43 megacities varies in a large range of -0.17 °C to 0.40 °C, reflecting their development level and growth rate. The results suggest possibilities of additional heat stress induced by urban warming to megacity dwellers and emphasize the importance of accounting for local urbanization in future urban climate projection.

A Roof Albedo Estimation of Individual Buildings by Super-resolution of Open Satellite Data

Kosho IDO1#+, Makoto NAKAYOSHI1, Shiho ONOMURA1, Sumika OYAMA1, Yuta WATANABE1, Ryo KANEKO2, Masuo NAKANO3, Yuya TAKANE4, Jeffrey JORDAN5, Matthew CROSS5, Benjamin CRAWFORD5
1Tokyo University of Science, Japan, 2The University of Tokyo, Japan, 3Japan Agency for Marine-Earth Science and Technology, Japan, 4National Institute of Advanced Industrial Science and Technology, Japan, 5University of Colorado Denver, United States

Incorporation of city-specific parameters such as the morphological, thermal, and radiative characteristics of urban surface in weather simulations is of great importance for accurate urban weather simulations. However, the problem is that such a database has not yet been established. Among them, this study focuses on the albedo of the roof surface, which largely influences the input of solar energy to cities. Since the actual roof albedo varies between individual buildings, it is necessary to have roof albedo data over a neighborhood to a city scale. Satellite images can be used to construct such albedo data over a city even over a global scale. Using commercial satellite data with high spatial resolution like World-View-3 (resolution = 1.24 m), we confirmed that the albedo estimation of individual buildings was possible with relatively high accuracy. However, it is costly to obtain such high-resolution images for all the cities over the globe. On the other hand, open satellite images cannot resolve most individual buildings; in particular, the spatial resolution of Landsat-8 is 30 m, and Sentinel-2 is 10 m. Using a Super-resolution algorithm with deep learning, we attempted to estimate the roof albedo from the Landsat-8 and Sentinel-2 data. Super-resolution is a technique that increases the resolution of an image by training a low-resolution image. Using a super-resolution technique, we propose an estimation method of albedo data from free satellite imagery. The model used for training was an edge-enhancement network (EEGAN). The generated intermediate image and enhanced edges can be combined to generate clear images with high credibility. We confirmed super-resolution images of Sentinel-2 resolved individual buildings and the albedo of the roof surface was obtainable. This model suggests the possibility of constructing a database of roof albedo for the cities over the globe.

Characteristics of Anthropogenic Heat Flux Estimated with Eddy Covariance Sites and Building Energy Consumption in Seoul, Korea

Seon-Ok HONG1+, Jinwon KIM1#, Sung-Hwa PARK2,1, Young-San PARK2,1, Sang-Sam LEE2,1, Yeon-Hee KIM1
1National Institute of Meteorological Sciences, Korea, South, 2Korea Meteorological Administration, Korea, South

With large populations and industrial activities as well as the energy, transportation, and water supply infrastructure for supporting them, anthropogenic heat flux plays an important role in shaping urban environments. Buildings are usually the leading anthropogenic heat sources in built-up urban areas. For example, building in Seoul consume nearly 90TWh annually. This building energy consumption is eventually released into their environment as heat. Because of large variations in human activities according to urban landuse, the urban anthropogenic heat emissions are expected to vary widely within urban regions.
This study analyzes annual anthropogenic heat flux (QF) in Seoul using eddy correlation data for two years (2017-2018) at various local climate zones (LCZ). The surface energy balance (SEB) for an urban canopy is Q*+QF<