Browse Abstracts

OS15 - Regional Oceanic Numerical Modeling and Observations
Oral Presentations
7/30/2019 8:30 AM-10:30 AM, 302
1 OS15-D2-AM1-302-001(OS15-A031)
Observed Mesoscale Eddies in the South China Sea
Guihua WANG#+
Fudan University, China

Observations of mesoscale eddies in the South China Sea have made an impressive progress in near two decades. The study is an overview of this progress. We will explore the eddy structures by combining satellite altimetry data and water temperature records from different platforms. These eddies’ life history including eddy propagation, eddy intensity will also be overviewed. Several mechanisms to trigger mesoscale eddies will be further disclosed. In addition, the observed interactions between ocean eddies and low level atmosphere will be discussed briefly.

2 OS15-D2-AM1-302-002(OS15-A002)
Mixing in the Indonesian Seas
Xiamen University Malaysia, Malaysia

The Indonesian seas have been referred to as the Indonesian “Mix-Master” since they transform the Pacific waters entering them into fresher, cooler Indonesian Throughflow water flowing out into the Indian Ocean. Tidal mixing due to the interactions of tides and the steep topography and sills of the Indonesian seas is believed to be the prominent mixing mechanism. However, there is also a mean flow coming through the region. The interactions of a mean flow and tidal currents modify the characteristics of the tidal mixing. To date, this has not been investigated or simulated for the Indonesian seas. We plan a combination modeling and observational program to investigate the tidal flow and the interactions of the mean flow with the tides and their impact on mixing and water mass transformation. The preliminary simulations have been completed. The simulations using observed hydrography cannot be completed until the observations are made. The observational effort will be focused on Ombai and Lombok straits; however, additional data will be collected off Bengkulu. The observational data will be compared to the simulations to verify the model is properly replicating the water mass transformation and mixing. Using the observation, the performance of different mixing schemes will be evaluated.

3 OS15-D2-AM1-302-003(OS15-A003)
Kuroshio-derived Pinch-off Mesoscale Eddies: Generation, Propagation, and Recollision with the Kuroshio
Yusuke UCHIYAMA1#+, Nobue OKADA1, Changming DONG2,3
1Kobe University, Japan, 2Nanjing University of Information Science & Technology, China, 3University of California, Los Angeles, United States

Mesoscale eddies are ubiquitous in the world ocean that frequently collide with currents and other eddies, leading to substantial alteration of the associated dynamics. To investigate fates and dynamical roles of pinch-off eddies from the Kuroshio Extension (KE) Jet, an eddy detection method was applied to ARMOR3D, a 3D global currents and density data set reconstructed from satellite and in-situ observations. Most of the detected pinch-off eddies are cyclonic on the south side of the KE region, while anticyclonic eddies are predominant on the north side. The former occurred 2.5–3 times as often as the latter, although in the entire North Pacific, cyclonic eddies occurred only 12.1% more frequently than anticyclonic eddies. We succeeded to determine pinch-off eddies recolliding with the Kuroshio by introducing another constraint, which is a threshold distance between the Kuroshio path and terminal positions of eddies. Comparisons of the surface temperature and salinity before and after the eddy collisions clearly exhibit that the alteration of the Kuroshio path due to eddy collisions is quite influential in modifying the oceanic structures. We found that the pinch-off eddies occasionally interact with other mesoscale eddies to modify the upper-ocean structure pronouncedly. It was also suggested that the stability of the Kuroshio path in the KE region is a key influencer on vigorous generation of such colliding pinch-off eddies.

4 OS15-D2-AM1-302-004(OS15-A004)
Biogeochemical Responses to Seasonal Oceanic Variability Along the Kuroshio
Xu ZHANG1#+, Yusuke UCHIYAMA1, Yota SUZUE2, Hidekatsu YAMAZAKI3
1Kobe University, Japan, 2CTI Engineering Co., Ltd., Japan, 3Tokyo University of Marine Science and Technology, Japan

Biological processes have significant influences on the global carbon cycle on all time scales. In the coastal regions, nutrient supply to the surface by river discharge and coastal upwelling leads to active primary production. The Kuroshio, one of the strongest western boundary currents, flows off the Japan, accompanied by intense eddy activities influencing on biogeochemical processes around its path. In general, localized upwelling due to mesoscale cyclonic eddies brings nutrient-rich subsurface water to the nutrient-depleted upper ocean to enhance near-surface primary productivity. In the present study, a climatological ocean modeling is developed for the marginal seas along the Kuroshio off Japan based on ROMS (Shchepetkin and McWilliams, 2005; 2008) coupled with an NPZD biogeochemical model (Fasham et al., 1990; Gruber et al., 2006). The model domain encompasses both the Kuroshio and its Extension regions in a submesoscale eddy-permitting configuration with a horizontal grid spacing of 3 km. The simulation is conducted for 10 years and the results for the 10th year are used for our analysis. A nitrogen budget analysis indicates that nitrogen exists mostly in the phyto- and zooplankton compartments in both the Kuroshio and Kuroshio Extension regions during the spring bloom. The increased zooplankton further enriches detritus that settles down by about 100 m, leading to an increase of ammonium below the mixed layer. In winter, eddy-induced nitrate transport is enhanced in the region about 1° away from the Kuroshio axis. The baroclinic instability due to the surface cooling in winter generates meso- and submesoscale eddies and substantially promotes eddy-induced vertical nitrate transport.

5 OS15-D2-AM1-302-005(OS15-A005)
Medium-term Water Mass Exchange and Associated Regional Circulations in the South China Sea
Naru TAKAURA1#+, Yusuke UCHIYAMA1, Nizamani ZAFARULLAH2, Akihiko NAKAYAMA2
1Kobe University, Japan, 2Universiti Tunku Abdul Rahman, Malaysia

A high-resolution, high-precision downscaling oceanic circulation model for the Southern China Sea (SCS) was developed based on the Regional Oceanic Modeling System (ROMS) at a lateral resolution of 5 km, initialized and forced by the Hybrid Coordinate Ocean Model global reanalysis product (HYCOM+NCODA 1/12 deg.). A multi-year reanalysis was conducted for the four-year period from 2012 to 2015 with the HYCOM-ROMS system that properly accounts for wind stress and heat budget at surface, freshwater influences from the atmosphere and major rivers, and tidal variability. The model results were confirmed to agree well with satellite and in situ measurement, and are generally consistent with the findings in previous studies. Prospective applications of the system include assessments of oceanic dispersal of wastewater, quantification of marine ecosystem network, analyses of micro plastic transport, its coastal accumulation and maintenance of offshore structure. In the present study, we utilized the model outcome to evaluate external forcing conditions on offshore oil platforms along the coast of the Malay Peninsular and Borneo Island by using extreme value statistics for surface currents and wind. The maximum surface currents were found off Borneo Island, which is influenced indirectly by the Mindanao Current remotely. It was suggested that water mass exchange between the Pacific and the SCS is extremely significant as it subsequently controls regional circulations in the coastal margins in the SCS.

6 OS15-D2-AM1-302-006(OS15-A006)
A Flood-induced Sediment and Suspended Radiocesium Transports in the Fukushima Coast Due to Typhoon 201326 Analyzed with a JCOPE2-ROMS Downscaling Model and in Situ Observations
Natsuki TOKUNAGA1#+, Yusuke UCHIYAMA1, Daisuke TSUMUNE2, Masatoshi YAMADA3, Yutaka TATEDA2, Yukari ITO4, Takashi ISHIMARU4, Yutaka WATANABE5, Ken IKEHARA6, Miho FUKUDA7
1Kobe University, Japan, 2Central Research Institute of Electric Power Industry, Japan, 3Hirosaki University, Japan, 4Tokyo University of Marine Science and Technology, Japan, 5Hokkaido University, Japan, 6National Institute of Advanced Industrial Science and Technology, Japan, 7National Institute of Radiological Science (NIRS), Japan

The Fukushima Nuclear Power Plant (FNPP) accidentally leaked substantial amount of radiocesium to the environment in March 2011. The radiocesium is known to have three input pathways to the marine environment: atmospheric deposition, direct discharge from the FNPP, and river discharges. The last process has lagged behind the accident by occasional floods that have delivered terrestrial deposition through hydrological processes. Therefore, the local coastal seas have suffered from continuous contamination due to riverine suspended radiocesium inputs that must be assessed carefully. Niida River has been a source of riverine suspended radiocesium even after the FNPP accident, as its watershed was prominently covered with the atmospheric deposition at the accident. We examined the oceanic dispersal and inventories of the sediments and suspended radiocesium deposited in the ocean floor derived from Niida River by using a quadruple nested JCOPE2-ROMS 3D oceanic circulation model coupled with a 3D multi-class sediment transport model along with a two-layer stratigraphy model of the marine bed, the iRIC-Nays 2DH river sediment transport model, the SWAN spectral wave model, and a static radiocesium absorption model. A particular attention was paid to the storm and subsequent flood event associated with Typhoon 201326 (Wipha) passed off Fukushima in October 2013, which provoked heavy precipitation, subsequent increase of the river discharge, and associated sediment and suspended radiocesium fluxes to the ocean. The model results were diagnosed with several in situ observed data collected in the Fukushima Coast after the storm. The modeled and observed lateral and vertical distributions of sediment grain sizes and attached radiocesium concentrations were reasonably well correlated each other. We then investigated the accumulation and erosion of the sediments and resultant suspended radiocesium distribution around the river mouth and nearshore areas along the Fukushima Coast.

7 OS15-D2-AM1-302-007(OS15-A042)
Freshwater Impact on Sound Speed Structure of the Bay of Bengal
Sudip JANA#+
Adamas University, India

The knowledge of sound propagation in ocean has wide range of scientific and strategic applications for underwater acoustic communication and remote observation of ocean interiors. The acoustic tomography has become an effective methodology for large scale ocean monitoring, and observation of ocean currents and internal tides. The variation of sound speed (SS) in the sea water depends on the variation of temperature, salinity and pressure. In general, temperature variation plays the dominant role in determining the SS variation. However, salinity variation has a significant impact on the SS variation in the regions of large salinity contrast. The Bay of Bengal (BoB) is one such region experiencing intense spatio-temporal salinity contrast. The enormous amount of freshwater input, mostly in its northern sector, from monsoon rain and from runoff of several adjacent rivers makes the northern BoB as the freshest region in the northern Indian Ocean. The freshwater input affects the sound speed in terms of modulating the salinity and temperature. The freshwater reduces the salinity of the surface layers of the BoB, which reduces the sound speed. The presence of low saline water in the surface layers results in formation of barrier layer that significantly modulates the subsurface temperature and supports the occurrence of subsurface temperature inversion during post-monsoon and winter. The existence of temperature inversion enhances the subsurface SS. In both the instances, the vertical gradient of SS in the upper layers gets enhanced, which eventually leads to strong surface ducting above the sonic layer depth.  In this study, the freshwater impact on SS has been analysed utilizing climatological atlas, in situ observations and model simulations.

8 OS15-D2-AM1-302-008(OS15-A040)
Summertime Upwelling Northwest Off the Hainan Island and its Mechanism
Ai-Jun PAN1#+, Fangfang KUANG2, Kai LI1, Junpeng ZHANG2
1Ministry of Natural Resources, China, 2State Oceanic Administration, China

A rarely seen upwelling phenomena northwest off the Hainan Island (UNWHI) is witnessed by the in-situ observation during July, 2015. Model simulation suggest that (1) the UNWHI is not a stationary phenomenon because it is the extension of upwelling west off the Hainan Island (UWHI) and located in the wake zone of the circling upwelling around the Hainan Island, (2) the generation mechanism for the UNWHI is tidal mixing and the favorable winds, where tidal mixing is the basic driving force and the local south westly winds is the necessary condition for the UNWHI’s occurrence, (3 net heat flux has limited effect on UNWHI,(4)variation of water temperature in NWHI and in WHI are highly correlated.

OS15 - Regional Oceanic Numerical Modeling and Observations
Oral Presentations
7/30/2019 1:30 PM-3:30 PM, 302
1 OS15-D2-PM1-302-001(OS15-A025)
Building the Kuroshio Extension Observational Network
Zhaohui CHEN1,2#+, Lixin WU1, Xiaopei LIN1, Xin MA1, Chun ZHOU1
1Ocean University of China, China, 2Qingdao National Laboratory for Marine Science and Technology, China

The Kuroshio extension region has been identified as a key location in the extra tropics in the North Pacific. Until recently, there have been quite limited high-resolution observations in the Kuroshio extension region. Here we review the observational work over the last two decades and report the recent observational work and future plan in the Kuroshio extension region. We aim to setup and maintain continuous and sustainable observations in this region.

2 OS15-D2-PM1-302-002(OS15-A010)
Deep Submesoscales: Elephant Seal and Satellite Unravel a Major Pathway Connecting the Ocean Interior to the Surface
Lia SIEGELMAN1#+, Patrice KLEIN2, Andrew THOMPSON1
1California Institute of Technology, United States, 2The French Research Institute for the Exploitation of the Sea (IFREMER), France

Vertical motions in the ocean are responsible for the transport and subsequent storage of heat, carbon and nutrients. To date, ocean mesoscale eddies (50-300 km) and small-scale diffusive mixing (<10 m) are traditionally invoked to explain oceanic vertical transport between the ocean interior and the surface. In addition, submesoscale motions (1-50 km) have also been identified as a key process for oceanic vertical transport but solely confined to the mixed layer. Here, using high-resolution observations collected by an elephant seal in the Southern Ocean, in combination with satellite altimetry data, we show that vigorous vertical motions (i) are associated with energetic submesoscale fronts located in-between mesoscale eddies, and (ii) extend from the surface down to depths of 500 m, i.e. well below the depth of the mixed layer. These intense submesoscale vertical motions, which locally exceed 200 m/day, are an important yet unexplored pathway connecting the ocean interior to its surface, and potentially has major implications for the biogeochemical and climate systems.

3 OS15-D2-PM1-302-003(OS15-A032)
Numerical Study of Multiple-scale Temporal Variations in 2016 Wind-wave and Wind in the Coastal Area Along the Northern Jiangsu Province, China
Xu JIN#+
Nanjing University of Information Science & Technology, China

Numerical Study of Multiple-scale Temporal Variations in 2016 wind-wave and wind in the coastal area along the northern Jiangsu Province, ChinaJin Xu, Yuhan Cao, Changming Dong, Weijun ZhuNanjing University of Information Science and Technology, Nanjing, ChinaWRF and SWAN models are applied to the study of wind and wave variations in the coastal area along the northern Jiangsu Province, China, WRF and SWAN model are used. The WRF model is used to simulate 10-m wind field in 2016, which is then used to drive the SWAN model. Modelled wind field and wave field in the offshore area of the northern Jiangsu is then obtained and analyzed. Observed data are used to verify the multi-scale changes of the wind field and wave field on the order of seasonal, intra-seasonal and diurnal variations and the changes of wind and wave fields under extreme conditions. The results show that the maximum annual effective wave height, average wave period, average wind speed and average wind direction in the offshore area of northern Jiangsu in 2016 are 2 m, 6.4 s, 3 m s-1 and northeast, respectively. The wind speed in winter is the largest, followed by autumn and spring, and smallest in summer; the wave height is highest in winter and lowest in summer; the effective wave height at 4 o'clock is the smallest, and the effective wave height at 14 o’clock is the largest.

4 OS15-D2-PM1-302-004(OS15-A012)
Global Navigational Satellite System Phase Altimetry of the Sea Level: Systematic Bias Effect Caused by Sea Surface Waves
Yaroslaw ILYSHIN1,2#+, Artem PADOKHIN3, Vladimir SMOLOV4
1Moscow State University, Russian Federation, 2Kotlenikov Radio Engineering Institute, Moscow, Russia, Russian Federation, 3Lomonosov Moscow State University, Russian Federation, 4Marine Hydrophysical Institute, Russian Federation

Inteferometric reflectometry is a relatively cheap technique for in situ measurements of the sea level surface, which can be implemented both at coastal stations of geodetic Global Naviational Satellite Systems (GNSS)-networks and specially organized observatories of global environmental monitoring. This technique, however, suffers from errors caused by sea surface perturbations. Surface waves are probably the most important source of random and systematic biases in the measured data. In this study, the technique of reflectometric altimetry of the local sea level is investigated both experimentally and theoretically. The reflections of radio waves of navigational space-borne radio beacons from undulating sea surface have been simulated numerically with the Finite Difference in Time Domain (FDTD) technique for different model spectra of the sea waves. Impact of the surface waves on the mean sea level estimate at the monitoring station location is investigated for low wave grazing angles, at which the interference between direct and reflected waves of GNSS is effectively observed with a single antenna. The simulation predicts that the bias of measured sea level is proportional to the surface wave height. Verification of this theoretical conclusion on the experimental data shows that for low and moderate wave profile heights (not exceeding the radio wave length) this systematic bias and the wave profile height are indeed proportional. Further increase of the wave profile height destroys the interference pattern, which prevents surface echo detection and estimate of the sea level. Nevertheless, for moderate surface waves the sea level measurements can be corrected for the bias effect, if the surface waves are independently registered and recorded. The research is carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University. Support from the Russian Science Foundation with the grant 17-77-20087 is kindly acknowledged.

5 OS15-D2-PM1-302-005(OS15-A035)
SAM Effects on Zonally Asymmetric Response of Ocean Mixing, Nutrients and Production in the Southern Ocean
Hui GAO1#+, Changming DONG1,2, Meibin JIN1, Hui ZHAO3
1Nanjing University of Information Science & Technology, China, 2University of California, Los Angeles, United States, 3Guangdong Ocean University, China

The unique physical features of the Southern Ocean set the stage for its crucial role in the global climate system. The Antarctic Circumpolar Current (ACC), a strong wind-driven eastward flow, has a profound influence on the physical and biogeochemical characteristics of the Southern Ocean. The Southern Annular Mode (SAM), the dominant mode of atmospheric variability in the Southern Hemisphere, influences the strength and the path of westerly wind belt surrounding the Antarctic as well as ACC. Temperature and salinity data from Argo profiling floats show that the SAM leads to zonal asymmetry in mixed-layer depth anomalies near ACC fronts. The mixed layer depth impacts on nutrient, phytoplankton and primary production deeply, however, the relationship between MLD and phytoplankton is complex. The MLD affects both the phytoplankton growth (nutrient concentration and light availability) and the phytoplankton grazing (zooplankton concentration). The effect of MLD on phytoplankton concentration could be immediate or lagged in time. This study uses 16 years of satellite data and Agro profiles to investigate the variations of chlorophyll and SAM effects on the zonally asymmetric response of mixing and nutrients in the Southern Ocean. One key aspect of our work is to distinguish the relationship between the mixed layer depth and surface phytoplankton blooms.

6 OS15-D2-PM1-302-006(OS15-A011)
Mass and Heat Transport Generated by the Kuroshio and Tides Investigated with a High Resolution Downscaled Regional Oceanic Model
Eiji MASUNAGA1#+, Waku KIMURA1, Taichi KOSAKO2, Yusuke UCHIYAMA3
1Ibaraki University, Japan, 2Port and Airport Research Institute, Japan, 3Kobe University, Japan

This study presents mass and heat transport processes associated with eddies caused by the interaction of Kuroshio and tides over the Izu-Ogasawara Ridge using a high resolution downscaled oceanic simulator. Both of the Kuroshio and tides largely influence physical processes off the south of the Japan mainland. The kinetic energy and sub-mesoscale eddies are significantly enhanced by tidal currents. The eddy enstrophy is increased due to the tidal forcing by a factor 10. The contribution of sub-mesoscale eddies to the kinetic energy and heat transport is evaluated by separating the current filed to eddy and mean components. The mean kinetic energy dominates in the total kinetic energy excepting near coastal regions. The eddy kinetic energy can explain roughly half of the total kinetic energy in the vicinity of Izu-Chain islands. Mean and eddy components play a different role in heat transport on the lee side of islands in the Kuroshio. Mean (eddy) heat transport decrease (increase) the surface water temperature on the lee side of islands. This implies that large scale motions generate upwelling to lower the surface temperature and small scale eddies transport warm Kuroshio water to the island wake. In addition, we conducted Lagrangian particle tracking simulations using modeled current data. The dispersion of particles released near the Izu-chain island is enhanced by the tidal forcing within the small time scale, less than 2 days. On the other hand, the dispersion is suppressed by the tidal forcing in the time scale longer than 5 days. The spectra of the particle velocity shows that low (high) frequency motions are decreased (increased) by the tidal forcing. The tidal forcing drives the conversion of large scale motions to small scale eddy motions, which results in the suppressed particle dispersion in the large and long scale. 

7 OS15-D2-PM1-302-007(OS15-A034)
SST Anomalies in the Mozambique Channel
Guoqing HAN1#+, Changming DONG1,2, Junde LI3, Jingsong YANG3, Yu LIU1
1Nanjing University of Information Science & Technology, China, 2University of California, Los Angeles, United States, 3State Oceanic Administration, China

Using both satellite remoting sensing SST data and numerical model results, sea surface temperature (SST) warm anomalies in the Mozambique Channel (MC) west of the Madagascar Island are found with respect to the SST east of the island along the same latitude. The mean SST inside the channel is up to about 3.0 ℃ warmer than east of the Madagascar Island. The anomalies exist all year round and the maximum value appears in October. The area of the highest SST is located in the northern part of the MC. Potential mechanisms causing the SST anomalies are discussed: Sea surface wind, heat flux and oceanic flow advection. The presence of the Madagascar Island results in weakening wind in the MC and in turn causes weakening of the mixing in the upper oceans, thus the mixed layer depth becomes shallow. The precipitation east of Madagascar is greater than that west of Madagascar because of orographic effects. Different precipitation patterns and types of clouds result in different solar radiant heat fluxes across both sides of Madagascar. Warm water advected from the equatorial area also contributes the SST warm anomalies.

OS15 - Regional Oceanic Numerical Modeling and Observations
Oral Presentations
7/30/2019 4:00 PM-6:00 PM, 302
1 OS15-D2-PM2-302-001(OS15-A038)
Submesoscale Instability in Idealized Mesoscale Eddies
Changming DONG1,2#+, Xingliang JIANG1
1Nanjing University of Information Science & Technology, China, 2University of California, Los Angeles, United States

Cyclostrophic and geostrophic balanced mesoscale eddies are subject to submesoscale instability. A high-resolution numerical model is developed to investigate the instability, which reveals how balanced mesoscale eddies are dissipated. Energetics analysis shows multiple instabilities (such as, symmetric, baroclinic instabilities) could take place in eddy decaying processes. It is also demonstrated that the high spatial resolution is required to reveal the decaying processes.

2 OS15-D2-PM2-302-002(OS15-A017)
Joint Effects of Physical and Biogeochemical Processes on the Formation of Hypoxia in the Pearl River Estuary
Zhongren ZHANG1#+, Jia-Tang HU1, Shiyu LI1, Bin WANG2
1Sun Yat-sen University, China, 2Dalhousie University, Canada

Hypoxia events frequently occurred in the bottom layer of the Pearl River estuary (PRE) from summer to mid-autumn, when the water column is highly stratified and restricts replenishment of oxygen from the atmosphere. The general consensus is that besides the physical processes, biogeochemical processes (algal production stimulated by excess riverine nutrients and sediment oxygen consumption (SOD)) in the ocean also plays an important role in the formation of the hypoxia. In this study, a three-dimensional (3-D) physical-biogeochemical coupled model was applied to provide dissolved oxygen data in PRE and describe the effects of other environmental factors, including seawater stratification affected by dynamic factors, primary productivity and sediment oxygen consumption. Based on the 3-D model, combined with some statistical analysis methods, the mechanisms controlling the formation, maintenance and dissipation of hypoxia in PRE were discussed in this paper. Model results showed that SOD and re-aeration play a major role in controlling bottom DO concentrations. While the high SOD due to the riverine inputs of particulate organic carbon could cause a significant decrease in the bottom DO concentrations by over 4 mgL-1 on the shelf off the Modaomen sub-estuary and lead to the formation of a high-frequency zone of hypoxia (HFZ), re-aeration could lead to an increase in the bottom DO concentrations, offset a portion of the DO consumed by SOD and keep the HFZ occurring in a small area. The re-aeration could also cause a strong vertical DO gradient, since the majority (similar to 89 %) of DO supplemented was transported to the lower layers through vertical diffusion and similar to 28% reached the bottom eventually.

3 OS15-D2-PM2-302-003(OS15-A021)
Submesoscale-resolving Observations in South China Sea by Fast-sampling Underwater Gliders
Ke MA1+, Zhaohui CHEN1,2#, Yanhui WANG3, Zhao JING1, Shuxin WANG3, Lixin WU1
1Ocean University of China, China, 2Qingdao National Laboratory for Marine Science and Technology, China, 3Tianjin University, China

Submesoscale-resolving observations in the northern part of South China Sea were conducted by three fast-sampling underwater gliders (Petrel Glider) in a 9-day consecutive fast-diving mission from April 26 to May 4, 2018. Each glider with a CTD sensor travelled across the front zone between a cold-core and a warm-core eddy and implemented more than 300 dives covering the upper 500m during the 170 km-trip. Detailed analysis indicate that the slope of wavenumber spectra of the potential energy is close to -2 in upper 50m, which is the typical mixed layer depth in spring. This implies there may exist submesoscale processes near the front formed by the adjacent warm/cold eddy, although it is relatively weak compared with the mid-latitude fronts near the strong western boundary currents. Further calculations of buoyancy gradient, balanced Richardson number and Ertel potential vorticity show that submesoscale instabilities would appear intermittently in the mixed layer. In particular, a strong unstable event was identified on May 3 when strong down-front wind destructed the stratification and induced further submesoscale instabilities.

4 OS15-D2-PM2-302-004(OS15-A024)
Observational Study on Turbulent Heat Flux Within a Warm Eddy in the Kuroshio Extension
Yueqi ZHANG1,2+, Zhaohui CHEN1,2#, Bin WANG3
1Ocean University of China, China, 2Qingdao National Laboratory for Marine Science and Technology, China, 3National Ocean Technology Center, China

Quantifying the turbulent heat flux (THF) is key to understanding the air-sea exchanges which constitute the ocean surface energy budgets on multi-time scales. By now, it still remains a big challenge due to lack of intensive in situ observations at high temporal and spatial resolution, with high accuracy. In particular, revealing the signature of oceanic eddies/fronts on the air-sea THF is beneficial to reduce uncertainties of high-resolution gridded products in regions of abundant eddies and fronts. Here we assessed the THF within a warm-core eddy to the north of the Kuroshio Extension in May/June 2018. Apart from underway observations by the research vessel, four newly-designed drifters called Drifting air-sea Interface Buoys (DrIB), which collected the sea surface temperature, air temperature, relative humidity, air-pressure and wind at 3m above the sea level, were deployed within the warm-core eddy for over three weeks. Preliminary analysis shows that the atmospheric variables and the associated THF change consistently away from the edge of eddy, that is, they vary spatially uniform within an eddy. We also found that the eddy-induced THF increase is not significant at this season, which is quite different from large heat flux release for a warm-core eddy during winter season. We suggest that the eddy-induced THF is of great seasonal dependence in the Kuroshio Extension region and it is also true for a case-study using the J-OFURO3 ocean flux data.

5 OS15-D2-PM2-302-005(OS15-A026)
Mapping of Sea Ice Leads and Melt Ponds from Multi-angle Imaging Spectro-radiometer Using Super-resolution Restoration
Yu TAO#+, Jan-Peter MULLER, Jennifer SUTHERLAND
University College London, United Kingdom

During the Arctic summer time, a large portion of the sea ice area contains melt ponds and sea ice leads. These features can absorb and store more heat, then gradually lead to more sea ice to melt. Effectively monitoring and modelling the sea ice leads and melt ponds are essential to calculate the radiative budget of the ocean, ice, and atmosphere system. In this work, we demonstrate capability of using the UCL MAGiGAN super-resolution restoration (SRR) system based on multi-angle feature restoration and deep SRR networks to produce up to a factor of 3.75 times resolution enhancement of the Multi-angle Imaging SpectroRadiometer (MISR) images (Tao & Muller, RS, 2018) to better support Sea ice leads and melt ponds modelling. The UCL MAGiGAN SRR system not only retrieves subpixel information from multi-angle distorted features, but also uses the losses calculated from feature maps of deep SRR network to retrieve high texture detail. In this work, 275m MISR red band L1B1 off-nadir images and one L1B2 nadir view reference image at a sea ice field located at (75.8º, -123.7º) are used to produce a 68.75m SRR image. Initial mapping results of sea ice leads and melt ponds will be demonstrated using MISR and SRR images in comparison with mapping these features in a 15m ASTER image. Evaluation and validation will be provided. The potential of using the UCL MAGiGAN SRR system for sea ice leads and melt ponds for future prediction of sea ice extent will be discussed. Acknowledgements: The research leading to these results is receiving funding from the UKSA Aurora programme (2018-2021) under grant no. ST/S001891/1 and received funding for QA4ECV from the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 607405

6 OS15-D2-PM2-302-006(OS15-A027)
Numerical Study of Coupled Air-sea Interaction During Typhoon Kalmaegi in the South China Sea
Kenny T.C. LIM KAM SIAN1#+, Changming DONG1,2, Hailong LIU3
1Nanjing University of Information Science & Technology, China, 2University of California, Los Angeles, United States, 3Shanghai Jiao Tong University, China

A typhoon represents an extreme case of air-sea interaction whereby fierce wind in the atmosphere forces considerable ocean response. Exchange of heat, momentum and mechanical energy is thus induced on both sides of the interaction. The Northwestern Pacific Basin is the most active typhoon basin on Earth, accounting for almost one-third of the world's annual typhoons. This study employs the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System during Typhoon Kalmaegi in the South China Sea in September 2014, to investigate the air-sea interaction processes of that typhoon event. Uncoupled and coupled model results are compared with best-track data from the China Meteorological Administration (CMA), reanalysis data from the National Centers for Environmental Prediction (NCEP) and European Centre for Medium-Range Weather Forecasts (ECMWF), satellite data from the Tropical Rainfall Measuring Mission Microwave Imager (TMI), and in-situ measurements from an array of 4 buoys along the typhoon path. Wind intensity shows reduced magnitude in the coupled model as compared to WRF-only results but the track is improved in the coupled model. The precipitation distribution is generally similar. However, less precipitation is observed in the simulation. The influence of the typhoon on the ocean is displayed in the obvious increase in ocean surface current magnitude as the typhoon moves past an area. Comparison with buoy data indicates that the simulation well resolves oceanic current variations. Significant Wave Height (SWH) generally shows similar patterns as that of the COAWST results as Typhoon Kalmaegi passes over the region. The main difference between ECMWF and simulated SWH is in their intensities - the latter is lower than the former. While one aspect on the typhoon simulation is improved during model coupling, another aspect gets worse. Several factors, including model settings, and thermal and dynamic processes, contribute to those differences. More sensitivity tests are required to make conclusions with confidence.

7 OS15-D2-PM2-302-007(OS15-A015)
An Atmosphere-wave Regional Coupled Model over the East China Sea
Delei LI1#+, Joanna STANEVA2, Sebastian GRAYEK 2, Arno BEHRENS2, Baoshu YIN1
1Chinese Academy of Sciences, China, 2Helmholtz Zentrum Geesthacht, Germany

The coupling of models is a commonly used approach when addressing the complex interactions between different Earth System components. This study focuses in the non-linear interaction between the waves and atmosphere models. Several sensitivity experiments have been performed to investigate the impact of atmosphere-wave coupling on the simulated wind and wave over the East China Sea. These experiments include stand-alone regional atmosphere model (CCLM) simulation, stand-alone spectral wave model (WAM) simulations driven by the regional atmosphere model CCLM or ERA5 reanalysis wind, and two-way (CCLM-WAM) coupled simulations. The two-way coupling is done interactively using OASIS-MCT libraries. The frequency of the exchange between CCLM and WAM is set to 6 minutes for the coupled run. We compared the simulated wind speed and significant wave height against in-situ and remote sensing data for 2010. Results show that the coupled model can be better in capturing the significant wave height during typhoon events. Considering the wave-induced stress led to improving the model skills during extremes, especially in the near-coastal areas. The validations of wind speed/significant wave height against satellite observations showed that the two-way model outperforms/underperforms both the stand-alone CCLM/WAM and ERA5 reanalyses. On the other hand, a comparison with wave buoy observations in the coastal areas demonstrates improvement of the two-way simulations in respect to stand-alone model or ERA-5 reanalyses. High-horizontal-resolution coupled model intensifies the simulation of storms compared to ERA-5 re-analyses .We demonstrate the differences between the different experiments in capturing the surface pressure, wind speed, roughness length field and vertical profiles (temperature, pressure and wind speed) to find out the interaction mechanism between atmosphere and wave.  

Poster Presentations
Seasonal and Spatial Variations of the M2 Internal Tide in the Yellow Sea
Kun LIU#+
Qingdao National Laboratory for Marine Science and Technology Development Centre, China

The seasonality of internal tides is particularly conspicuous in shelf seas due to the dramatical variations in the marine environment. In this paper, the seasonal and spatial variabilities of M2 internal tides in the Yellow Sea (YS) are investigated using a high-resolution numerical ocean model. The freshwater runoff of the Yangtze River is also considered. Because most nonlinear internal waves are of tidal origin, the simulated internal tides show good spatial consistency with the satellite-detected nonlinear internal waves. During summer, the M2 internal tides are ubiquitous and originate from multiple generation sites (e.g., the west coast of the Korean Peninsula and the Yangtze River estuary). During other seasons, the spatial coverage of the internal tides becomes very limited. Multiple sources combined with seasonal onset and decay lead to complex seasonal interference patterns. The wavelengths vary both spatially and temporally, depending on the water depth and ocean stratification. Between spring and autumn, a seasonally reversed pattern of radiation of baroclinic energy flux is found in the southern YS, which may be induced by the seasonal variability of the Yellow Sea Warm Current. Seasonal stratification controls the seasonality of the generation, propagation, and dissipation of internal tides and, is maintained by the monsoon, seasonal circulation and Yangtze River runoff. Our simulations suggest that, although internal tide dissipation is dispensable for the tidal energy budgets in the YS, internal tides seem to be the leading order contributor to the mid-column diapycnal mixing, as they are more efficient mixers than barotropic tides.

Impact of Wave Induced Turbulent Kinetic Energy on Tropical Cyclone in Regional Atmosphere-ocean-wave Coupled Model
Masashi TAKAGI1#+, Nobuhito MORI1, Junichi NINOMIYA2
1Kyoto University, Japan, 2Kanazawa University, Japan

The upper ocean mixing (UOM) is important phenomena to exchange thermal energy between atmosphere and ocean. The UOM effects on sea surface temperature (SST) reduction and gives substantial influence on control tropical cyclone (TC). We analyzed field observed data targeting typhoons in Shirahama field observatory tower, Wakayama, Japan and obtained wave induced total turbulent engage (TKE) flux from waves to ocean. The TKE flux from the surface can be parameterized as a function of wave energy dissipation, relative angle between wave and wind direction and wave steepness. The new parameterization for TKE flux is implemented into WRF-ROMS-SWAN coupled model (COAWST). The sensitivity of TKE flux parameterization to tropical cyclone is examined targeting super Typhoon Haiyan in 2013.The impact of surface TKE flux on coupling model for super typhoon characteristics will be presented at the conference.

How Does Wave Directional Distribution Affect the Likelihood of Rogue Waves?
Mark ORZECH#+, Jie YU
U.S. Naval Research Laboratory, United States

This modeling-based study seeks to quantify the likelihood of rogue (or freak) wave development in the deep-water ocean under varying wave directional distributions. While linear phenomena such as wave superposition can contribute to extreme waves, here we also examine nonlinear contributors, which are not always represented in operational wave models. The fundamental nonlinear phenomenon considered is frequency modulation via the so-called “Benjamin-Feir” instability, which requires a relatively narrow-banded wave frequency distribution to be activated. The wave directional distribution can also influence the growth rate of this modulational instability. If the energy of a given wave spectrum is broadly distributed over a wide range of directions (i.e., a large directional spread), the opportunities for frequency modulation are reduced and the likelihood of rogue wave development declines. In contrast, if the wave directional distribution is narrow and/or bimodal (i.e., energy peaks at two distinct directions), nonlinear modulation and extreme wave growth can be enhanced. The relative “intensity” and wave-amplifying effects of a range of directional distributions were quantified using a series of simulations with the higher-order spectral model HOS-Ocean (Ducrozet et al., 2007). Model output was in qualitative agreement with published theory. Test results were analyzed to develop an empirical formulation for extreme wave likelihood as a function of a directional spread and bimodality. The formulation is presently being evaluated by correlating likelihood estimates with wave data from ocean buoys, with identified rogue wave events interspersed among longer surface elevation time series.

Regional Scale Seawater CO2 System Modeling in Coral Triangle Area: Preliminary Results
Faisal AMRI1,2#+, Takashi NAKAMURA1, Lawrence Patrick Cases BERNARDO1, Kazuo NADAOKA1
1Tokyo Institute of Technology, Japan, 2Institut Teknologi Bandung, Indonesia

The Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system (ver. 3.3; Warner et al., 2008, 2010) coupled with a biogeochemical model (Nakamura et al., 2018) was applied in simulating seawater COsystem in Coral Triangle Area. The model domain stretched from 18oS-29oN; 90oE-164oE with 0.08o× 0.08grid resolution, and with year of 2016 as simulation period. TPXO Tidal Solutions and 3 hourly Japan ReAnalysis (JRA-55) data products were used as tidal and atmospheric forcing for this model, respectively. Interpolated 0.08HYCOM results were used as initial and boundary conditions for ocean model. Polynomial regression analysis using HYCOM temperature results and GLODAP dataset compilations from 1999-2010 was performed to estimate Total Alkalinity (TA), Total dissolved Inorganic Carbon (TIC), and Dissolved Oxygen (DO) for the biogeochemical model’s initial and boundary conditions. Calculation of Willmott’s skill score for modeled temperature and salinity in comparison with daily TAO-TRITON and RAMA mooring arrays' data gave results ranged from 0.85 – 0.95 and 0.74 – 0.84, respectively. The 10-m depth modeled velocity also showed reasonably good agreement with 3 out of 6 moorings that selected for the ocean model assessment. Comparison of modeled sea surface elevation with UHSLC “research quality” data in 12 observation points showed the highest rvalue of 0.63 and model skill of 0.87 was achieved by the model. Modeled COsystem parameters was compared with available observation results for inner Indonesian seas showed that modeled TA and TIC ranged from 2230 – 2278 μmol kg−1and 1882 – 1989 μmol kg−1, respectively, while collected observation value ranged from 2014 – 2360 μmol kg−1and 1748 – 2303 μmol kg−1, respectively. Low values of modeled pCO2 in low latitude area imply that the area acted as a sinkof CO2, which contradicted previous studies' results, and hence emerged the needs for model improvement.

Analysis on the Spatial and Temporal Sensitivities of Key Parameters in Swan Model: An Example for Chan-hom Typhoon Waves in the East China Sea
Yao XU1+, Jicai ZHANG2#, Yun XU2, Wangmin YING2, Yaping WANG1, Zhumei CHE3, Ye ZHU3
1Nanjing University, China, 2Zhejiang University, China, 3The Ocean and Fisheries Bureau, China

Based on the third-generation wave model SWAN, waves in the East China Sea caused by Typhoon Chan-hom (1509)are simulated, forced by CCMP (Cross Calibrated Multi-Platform) wind data and calibrated by observations at 4 buoy stations along the eastern coast of China; especially, the spatial and temporal sensitivities of the significant wave height (SWH)to the key parameters in SWAN model in the typhoon forcing range and period are studied, including wind input and white-capping, bottom friction, depth-induced wave breaking and nonlinear quadruplet wave interactions. The results show that in general, SWH is most sensitive to the wind input and whitecapping term, then the bottom friction term and the breaking term. But in shallow water, the SWH is most sensitive to the parameter gamma, which means the ratio of maximum individual wave height over depth, of depth-induced wave breaking. After a certain depth, the sensitivities of wind input and whitecapping parameters on the SWH begin to be stronger than other parameters. This threshold depth depends on sea states. The higher the sea state, the deeper the threshold depth. In general, the sensitivity is greater in coastal areas in space. The four different numerical procedures of four-wave interactions(so-called quadruplets) mainly affect the distribution of wave energy, not the SWH. In addition, the SWH is most sensitive to the drag coefficient and bigger wave means more sensitive. The study of spatial and temporal sensitivities of key parameters is of great significance for further application of SWAN model and wave simulations, especially typhoon wave simulation.

Numerical Modeling of Storm Tides over the Maritime Continent
Bijoy THOMPSON1#+, Pavel TKALICH1, Jianyu LIU2, Xiangming SUN2, Claudio SANCHEZ3, Xiang-Yu HUANG2
1National University of Singapore, Singapore, 2Centre for Climate Research Singapore, Singapore, 3UK Met Office, United Kingdom

A storm tide is the combination of sea water level rise due to storm surge and astronomical tide where the storm surges are caused by strong winds. Meanwhile, the tides originate by the gravitational pull of the sun and the moon. A high-resolution (4.5 km x 4.5 km) tide-only and tide plus wind forced ocean model configurations have been developed for the Maritime Continent (MC) (90°E to 141°E and 18°S to 25.6°N). Barotropic regional configuration of the Nucleus for European Modelling of the Ocean (NEMO3.6) ocean model has been used in the study. Tidal elevations and currents corresponding to 15 major constituents obtained from the Finite Element Solution tide model (FES2014b) are used for providing the tidal harmonics at the lateral boundaries. Hourly varying 10-m surface wind from ERA5 atmospheric reanalysis data is also included as the surface boundary condition in the tide plus wind forced experiments. The ocean bottom friction is computed using the quadratic formulation. A set of experiments with a constant as well as spatially varying bottom friction coefficients are performed to improve the accuracy of tide sea level simulations. Sea level simulated by the NEMO tide-only models are compared with the corresponding tidal harmonics data estimated from 28 tide gauge stations across the domain. Further, the analysis of storm tides simulated by the model and their comparison with tide gauge observations are performed.

Impacts of Relative Vorticity on Critical Latitude Effects on Internal Tides, Waves, and Mixing
Tianyu ZHOU1#+, Zhibo SHAO1, Weihong LIN1, Jiarui CHEN2, Muzhi ZHOU2, Paul HARTLIPP3, Robin ROBERTSON2
1Xiamen University Malaysia, China, 2Xiamen University Malaysia, Malaysia, 3University of New South Wales, Australia

Internal tides are believed to be the major contributor to mixing for the ocean’s interior. At the critical latitudes, where the tidal frequency equals the inertial frequency, resonant effects come into play and mixing increases. Generally, the critical latitude is thought to be an exact latitude, but really both the relative and planetary vorticities are important with the relative vorticity shifting and/or broadening the critical latitude effects. These shifts can be up to 5o of latitude, depending on the relative vorticity. The oceans are full of relative vorticity, from various sources, with the major contributors including horizontal shears in the major currents and in locally generated currents and eddies. We investigated the interactions of different vorticity fields on the critical latitude effects associated with internal tides, internal waves, and mixing from the interactions of tides with a seamount. We found both broadening of the range of critical latitude effects and shifts in the critical latitude. Mixing was increased poleward of the critical latitudes when relative vorticity from background currents was present.

Online Isolation of Near-inertial Internal Waves in Ocean General Circulation Models
Zhuo SONG#+, Zhao JING, Lixin WU
Ocean University of China, China

Near-inertial internal waves (NIWs) play an important role in furnishing ocean diapycnal mixing. However, parameterization of NIW-induced mixing in high-resolution ocean general circulation models (OGCMs) remains a challenging problem partially due to the lack of appropriate tools for isolating NIWs during the model integration. In this study, we propose two new methods feasible for online isolation of NIWs in high-resolution OGCMs, i.e., the two-step filter and three-step filter. The two-step filter only requires the velocity records to be stored at two time steps. It performs reasonably well in isolating NIWs poleward of 30 degrees if the time step is set as 6 h. By utilizing the velocity information at one additional time step, the three-step filter with a time step of 6 h generally outperforms the two-step filter in the global ocean. Specifically, the three-step filter results in reasonable isolation of NIWs poleward of 15 degrees where the NIW-induced mixing is strongest.

In-situ Measurements of Bottom Boundary Layer in Mariana Trench
Qian LIU1#+, Haiqin DUAN2, Zhiwen WANG2, Meng LIU1, Jingping XU1
1Southern University of Science and Technology, China, 2Ocean University of China, China

Advancements of instrumentation technology have enabled more researchers to explore the Mariana Trench, the deepest spot on earth, for the first time. In an attempt to investigate the bottom boundary layer properties in the trench, two Free Ascending Tripod (FAT) systems equipped with Conductivity-Temperature-Depth (CTD) sensors, Acoustic Doppler Current Profilers (ADCP), transmissometers, and high-resolution video cameras were placed on the south slope of the Challenger Deep, at 5959 m and 6021 m water depth respectively, for 14 months (February 2017 to April 2018). The near bottom (~6000 m depth) water mass is typical low temperature, high salinity deep ocean water. The θ-S diagram from the CTD data suggests a fairly uniform and stable environment, at least for the first two mouths of the deployment (March to April 2017) when CTD data was available. The measured transmissivity was near 100%, resulting from the super clean water where the ADCP frequently failed to work properly due to lack of scatters in the water column. The measured currents fluctuated in a range of 0-16 cm/s, which the last bottom layer's velocity gets to 16.3cm/s, with directions changing sharply within 9 to 17 m above the bottom. The residual current on the south slope of the Challenger Deep is generally to the east, seemingly corroborates with previous findings of a cyclonic geostrophic flow in the trench.

Submesoscale Eddies in the East China Sea Revealed from SAR Images
Yuxiang JI1#+, Guangjun XU2, Changming DONG1,3
1Nanjing University of Information Science & Technology, China, 2Guangdong Ocean University, China, 3University of California, Los Angeles, United States

The study uses Synthetic Aperture Radar (SAR) images from 2005 to 2011 to analyze eddies in the East China Sea. A total of 112 images are selected from 3000 images. In the 112 images, 153 eddies are detected according to the characteristics of eddies. It is found that the scale of ocean eddies observed from SAR images is small, and most of them are sub-mesoscale cyclonic eddies. Seasonal differences in the distribution of eddies are found, which displays highest number in summer and lowest number in winter. Since slick streaks in SAR images look dark, eddies due to slicks are referred to as "black eddy". As a result of wave-current interactions in the zones of current shear, bright curve lines are observed, which are called "white eddy". During the 7 years, 101 black eddies and 52 white eddies are observed in the study area. Black eddies are found in the whole study area, and white eddies are mainly distributed in the vicinity of the Kuroshio. More white eddies are found around the Kuroshio because of the strong shear in the Kuroshio region. In terms of the size of the eddies, the size of the white eddies is generally smaller than that of the black eddies.

Numerical Study of Long-term Variation of Salt-water Intrusion in Yangtze River Estuary
Haiyun SHI1#+, Changming DONG1,2, Chunhui LI1
1Nanjing University of Information Science & Technology, China, 2University of California, Los Angeles, United States

Salty water intrusion at the estuary of the Yangtze River, the third longest river in the world, is investigated using the Unstructured Grid, Finite-Volume Coastal Ocean Model (FVCOM). The model is integrated for 25 years from 1993 to 2017. River discharge, tide, zonal wind and meridional wind are used to analyze their impacts on the salt-water intrusion. The river discharge is the most important factor and its correlation coefficient with the intrusion distance is -0.875. In addition, the meridional wind also has a big impact on the intrusion and their correlation coefficient reaches -0.561. Some special salt-water intrusion events are also examined in detail in order to figure out the impact mechanism.