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Oral Presentations

OS17 - Regional And Coastal Ocean Modeling And Observations
Wednesday, August 03, 2016 | 303A (L3S) | 08:30-10:30
OS17-D3-AM1-303A(L3S)-001 (OS17-A033)
An Anatomy of the South China Sea Circulation
Dake CHEN#+, Weibin GUAN, Xiaohui LIU
State Oceanic Administration, China
#Corresponding author: +Presenter

The basin-scale circulation of the South China Sea (SCS) has been a subject of great interest, not only because of its importance in regional climate and environment, but also because of its potential role in global ocean circulation. Therefore, the SCS circulation, especially the shallow wind-driven gyre, has been studied extensively in the past, in terms of data analysis as well as numerical modeling. However, there is still a lack of dynamical understanding of the structure and genesis of the three-dimensional SCS circulation, including both wind-driven and thermohaline components. Here we try to perform an anatomy of the SCS circulation using a set of diagnostic, theoretical and numerical models. Our diagnostic analysis based on GDEM data indicates that the SCS circulation has a distinctive 3-layer structure, with an anticyclonic mid-layer sandwiched by cyclonic surface and bottom layers. Our theoretical model, based on mass conservation and beta-plane geostrophic balance, suggests that such a structure can be interpreted as a three-dimensional overturning circulation induced by the deep and surface inflows at the Luzon Strait, with a surface intensification by wind forcing. Finally, our numerical experiments demonstrate that the strong mixing in the SCS is largely responsible for the thermohaline SCS circulation as well as the water exchange between the SCS and the Pacific Ocean.

OS17-D3-AM1-303A(L3S)-002 (OS17-A038)
Internal Tides Off Eastern Australia
University of New South Wales, Australia
#Corresponding author: +Presenter

Barotropic and baroclinic tides simulated for the waters off eastern Australia in the Coral and Tasman Seas.  Tides were found to impact the mean current, East Australian Current (EAC), enhancing the mean flow by 1-4 Sv in some regions.  The southward flow increased over the continental shelf.  Tides did not appear to impact eddy formation; however they affected both the rotation within the eddy and the eddy. Cyclonic eddies rotated faster with tides and anticyclonic eddies slower.  Cyclonic eddies also propagated faster with tides than without tides.  Tides impacted cross-shelf transport of cold waters, with significantly more transport occurring in the tidal simulations.  Although the mean currents and eddies were the prime sources of the vertical shears inducing vertical mixing, tides played a role.  Tides influenced mixing by increasing vertical temperature diffusivities by 10-4 to 10-3 m2 s-1 over portions of the continental slope and over rough topography, particularly in regions near the diurnal critical latitudes (27o-30o).  In conclusion, even small tides significantly impacted the mean currents, eddy rotation velocities and propagation, and mixing.

OS17-D3-AM1-303A(L3S)-003 (OS17-A044)
Towards Downscaling Small-Scale Coastal Dynamics
Helmholtz Zentrum Geesthacht, Germany
#Corresponding author: +Presenter

Temporal developments and changes of small-scale coastal dynamics are commonly not well described by observational data sets or climate change simulations. On the other hand, such changes may be of particular interest for planning measures to deal with such changes. We suggest to apply the "empirical downscaling"-concept for consistent specifying of such changes. This needs building links between large-scale states and small-scale statistics. For doing so suitable data sets are needed, which are homogeneous in space and time, and extend across several decades or more.

We have examined the simulation STORM with the 0.1 grid resolution ocean GCM MPI-OM forced with NCEP atmospheric re-analyses; by comparing the variability of sea surface height from the simulation with satellite data and an ocean reanalysis, we found a good similarity between the different data sets. We conclude that STORM is suitable for developing empirical downscaling models. Using this data set we have derived first such models dealing with coastal upwelling in the South China Sea.

OS17-D3-AM1-303A(L3S)-004 (OS17-A014)
Utilizing a Regional Ocean Model for Weather Routing for Optimal Vessel Navigation
Kenta KUROSAWA1#+, Yusuke UCHIYAMA1, Taichi KOSAKO2, Hiroaki TADA1
1 Kobe University, Japan, 2 Port and Airport Research Institute, Japan
#Corresponding author: +Presenter

Social demand has been grown for improving fuel efficiency in vessel navigation to reduce emission of green house gases. Since vessel navigation is affected significantly by ambient oceanic and atmospheric conditions that restrict the optimal routes, weather routing is strongly required for desirable navigation. In the present study, we attempt to utilize a regional ocean model (ROMS) for marine weather routing along with published weather and oceanic reanalysis/prediction. Data retrieval in prior to departure and subsequent onboard prediction are essential because sufficient data retrieval through communications satellites during voyage is total unfeasible.  The developed weather routing system (WRS) is based on the A-star algorithm, a descendant of the commonly used Dijkstra algorithm in graph theory. A cost function is additionally introduced to account for oceanic and atmospheric conditions around the vessel of interest. Three options are considered to search for the optimal paths with the shortest travel time, the minimal fuel consumption, and the shortest travel distance.

Four experiments are conducted with the developed WRS, atmospheric and oceanic reanalysis as well as in-house ROMS simulations to evaluate the optimal vessel paths for 1) ocean lanes between Tokyo and Okinawa where the northeastward drifting Kuroshio is a key factor, 2) same as 1) but under a typhoon condition, 3) coastal lines in the Seto Inland Sea where transient tidal currents are most influential on the navigation, and 4) evacuation of fishery boats after the leakage of radionuclides from the Fukushima Dai-ichi Nuclear Power Plant. All these applications successfully demonstrate that the optimal vessel paths are pronouncedly dependent on oceanic and atmospheric conditions.  Furthermore, a compact ROMS executable on laptop PCs is configured for a vessel-borne WRS and is successfully applied to problem 3) where high-frequency tidal currents modified by complex topography are predominant.

OS17-D3-AM1-303A(L3S)-005 (OS17-A021)
Exchange of Water of Lake Pontchartrain with Coastal Ocean Through Multiple Inlets Forced by Atmospheric Cold Fronts
Wei HUANG#+, Chunyan LI
Louisiana State University, United States
#Corresponding author: +Presenter

Cold fronts induced exchange of water of lake estuaries through multiple inlets with the coastal ocean is studied using data obtained from  acoustic Doppler current profilers ( ADCPs) and high resolution wind field simulated by Weather Research and Forecasting model (WRF). Our focus is the response of hydrodynamics to atmospheric cold fronts, a common weather phenomenon that intensifies in winter times. Three ADCPs were deployed from Oct 09 to Nov 18, 2008 in the three main inlets of Lake Pontchartrain including the Rigolets, Chef Menteur and Industrial Canal. By applying Fourier Transform and low pass filtering to the data obtained from ADCPs, the sub-tidal characteristics of water level and current velocity response to cold front events during winter time are analyzed. We found that the sub-tidal hydrodynamic responses are highly correlated with the meteorological factors: meteorological factors during cold front events with longer duration are able to induce hydrographic responses for a longer time; water levels tends to decline when air pressure increases; water flows out of Lake Pontchartrain through multiple inlets under northerly winds; long period of easterly winds can cause water to flow into the lake through multiple inlets. To further investigate the structure of current in the lake estuary and the water exchanges for multiple inlets, a numerical model (FVCOM) is applied. Wind fields with higher space and time resolution simulated by WRF model are taken as the initial input for the ocean model , thus further interpreting how do the hydrodynamic variables respond to cold front events in winter time and what are the main mechanism driving them. 

OS17-D3-AM1-303A(L3S)-006 (OS17-A022)
A Comparative Analysis of Existing Models for Diffuse Attenuation Coefficient of Downwelling Irradiance with a Special Emphasis on Natural Waters
Leonid SOKOLETSKY1#+, Vladimir BUDAK2
1 East China Normal University, China, 2 Moscow Power Engineering Institute (Technical University), Russian Federation
#Corresponding author: +Presenter

The diffuse attenuation coefficient of downwelling irradiance Kd is an important water property describing the rate of change of irradiance with depth, and it related to such indices of water quality as turbidity and concentrations of components in the water. We have analyzed an impact of such parameters as of the single scattering albedo (0.1 to 0.99), backscattering probability (0.00869, 0.1559, and 0.4986), wavelength (490 nm), solar zenith angle (30.5 deg), cloudiness C (0 to 1), diffuseness of irradiance dE (0 to 1), and optical depth for the diffuse attenuation coefficient (0, 1, 2.3, 4.6) on the Kd by 12 analytical literature models. We also compared results with computations performed by numerical, highly accurate radiative transfer model (modified discrete ordinates method). We have used a synthetic dataset covering any possible values of parameters typical for natural waters. A comparison has shown that the most of the analytical models yield very close results to one another, simultaneously demonstrating a high correlation with the numerical method. A study has shown that an accuracy of the models generally increases with increasing the optical depth and decreasing B and  dE). At the typical value of B = 0.00869 for natural waters and within the first optical depth, the best results demonstrated Pan and Zimmerman (2010), Lee et al. (2005), Gordon (1989), Kirk (1991), Aas (1978), and Ben-David (1995) models. These six models yielded normalized (relative to observed average) root-mean-square errors of 7.1%, 7.4%, 8.9%, 9.6%, 10.0%, and 10.0%, respectively, at clear sky (C = 0, dE = 0.345) and the Kd averaged within the first optical depth. Thus, this study gives an additional confidence for application of different simple analyticalKd models in in situ and remote sensing studies of natural waters.

OS17-D3-AM1-303A(L3S)-007 (OS17-A041)
Optical Absorption Properties and Mixing Behavior of CDOM in the Spring Pearl River Estuary
Xia LEI#+, Jiayi PAN
Chinese University of Hong Kong, Hong Kong SAR
#Corresponding author: +Presenter

Deep understanding of optical absorption properties and mixing behavior of CDOM in estuary is necessary for tracking coastal organic carbon transport using satellite remote sensing data. 88 water samples were collected in the Pearl River Estuary (PRE), China during a cruise in May 2014, to measure spectral absorption of chromophoric dissolved organic matter (CDOM), together with their salinity. Over a salinity range of 0-30, CDOM absorption coefficients at 355 nm (a(355)) ranged from 0.197 to 5.557 and the spectral slope in the UV domain (S275-295) extended from 0.012 to 0.029. Significant negative power-exponential relationship was found between a(355) and S275-295, illustrating a decrease of CDOM absorption decay rate in the UV domain with an increase of absorption coefficient. The M value, which indicates CDOM molecule composition, were calculated by a ratio of a(250) to a(365). Regression analysis showed some linear relationships existed between M value and a(412) and S275-295, which revealed the contribution of molecule composition to CDOM absorption coefficient and its spectral decay rate in the UV domain. Mixing behavior of CDOM accompanied with the mixture of fresh water and seawater in the PRE was investigated along the salinity magnitude. Both a(230) and S275-295 were found to have obvious negative linear relationship with salinity, indicating the CDOM concentration change in the PRE is mainly influenced by the physical mixing of fresh water and seawater. Insignificant linear relationship between M value and salinity proved that CDOM molecule composition was less influenced by the water mixture in the estuary. 

OS17-D3-AM1-303A(L3S)-008 (OS17-A047)
Comparison of Field Current Data Near Mailiao Harbour with High Resolution Model HYDROMAP
Kuo-Tung CHANG#, San Sieu CUONG+, Chao-Hsiang CHEN, Yi-Ting TSAI, Jheng-De LI
National Kaohsiung Marine University, Taiwan
#Corresponding author: +Presenter

Water-velocity profiles were collected at MaiLiao Harbor in the North Western YunLin County, Taiwan, from January to December 2015, using an Aquadopp current profiler. These data are a series of 10-minute-averaged water velocities collected at 1 meter vertical intervals (bins) in the 10-meter water column, beginning 1 meters above the sea bed. To examine the vertical structure of the horizontal water velocities, the collected data were separated into individual time-series by bin and processed in time-series and rose plots.

Analysis of the time-series data from each bin is employed to investigate the characterization of bottom topographic effects to both current direction and speed. In addition, elaboration of the driven-force to the tidal variation during low tide and high tide periods to the characteristics changes of current is also observed. The present study evaluates the correlation of mean flow magnitude fluctuation among different profiles, especially the upper and near bottom water layers. Finally, the accuracy of the data and the potential disturbance of measurements from field observation using Aquadopp current profiler are comprehensively compared and validated with reliable and predictive current data output from HYDROMAP.

Keywords: Aquadopp current profiler, current measurement, water-velocity profile, HYDROMAP

OS17 - Regional And Coastal Ocean Modeling And Observations
Wednesday, August 03, 2016 | 303A (L3S) | 16:00-18:00
OS17-D3-PM2-303A(L3S)-009 (OS17-A042)
Observation and Modeling of the Mesoscale Eddies at Xisha Water
Dongxiao WANG#+
South China Sea Institute of Oceanology, China
#Corresponding author: +Presenter

Analyzing the observed currents at Xisha (110.3899oE, 17.1038oN) , it is found that the kinetic energy has significant mesoscale variability, and each peak responds to large positive/negative ocean surface current curl caused by mesoscale eddies. Compared the kinetic energy with the wind stress work and the pressure work, it is also found that the barotropic pressure work which is mainly contributed by the sea surface height (SSH) corresponding to the mesoscale eddies behaves like the kinetic energy. The contribution of the mesoscale eddies to the kinetic energy can be up to 90% sometimes and reach deep level every time. And a deep energetic and baroclinic eddy is detected in this station with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.

OS17-D3-PM2-303A(L3S)-010 (OS17-A025)
Upper Ocean Dynamics and Associated Water Exchange at the Entrance of a Semi-Enclosed Bay Based on an In-Situ ADCP Measurement
Yusuke UCHIYAMA1#+, Tomomichi YOSHIKI1, Hiroaki TADA1, Yasuyuki BABA2, Hideaki MIZUTANI2, Teruhiro KUBO2, Nobuhito MORI2, Ayumi SARUWATARI3, Junichi OHTSUKA4, Junichi NINOMIYA5, Yasunori WATANABE3, Tomohito J. YAMADA3
1 Kobe University, Japan, 2 Kyoto University, Japan, 3 Hokkaido University, Japan, 4 Public Works Research Institute, Japan, 5 Kanazawa University, Japan
#Corresponding author: +Presenter

Quantification of hydrodynamics and associated mass exchange are of great importance towards a desirable coastal management of water quality and marine environment in semi-enclosed embayment. Tanabe Bay, Wakayama, Japan, located along the west coast of Kii Peninsula is chosen for the study site. A previous numerical study demonstrated that mass exchange at the bay mouth is predominantly occurred with semi-diurnal internal tides and subtidal variability attributed to the fluctuating Kuroshio through mesoscale recirculation (Uchiyama et al., 2014). The present study aims at describing upper ocean dynamics and resultant volume transport at the bay mouth based on a comprehensive field campaign conducted in summer to fall of 2015.

The vertical structure of transient upper ocean dynamics and consequent water exchange are characterized by high-frequency variability peaked at around the semi-diurnal band as well as in lower-frequency subtidal bands for 2-3 day period, consistent with the previous modeling study. A spectral coherence analysis illustrates that near-surface currents are mainly driven by wind stress peaked at the diurnal frequency, whereas subsurface currents fluctuate rather by semi-diurnal internal tides. In addition, barotropic response is established within the surface boundary layer since tidal elevation is well correlated with velocity at all the depths. Prevailing outgoing mass flux is observed from the time-averaged transport in the surface layer while the lower layer transport occurs as incoming mass fluxes. The vertical profile of temperature exhibits that the upper ocean cools down gradually, corresponding to seasonal transition from summer to fall condition. However, a week-long abrupt cooling event is observed. Interestingly, local forcing including wind, waves, and tides does not cause this upper ocean cooling, but an offshore subtidal intrusion of cold water induced remotely by fluctuations of the Kuroshio path is found to play an essential role, according to satellite SST data.

OS17-D3-PM2-303A(L3S)-011 (OS17-A006)
Seasonality of Tides in Southeast Asian Waters
Adam DEVLIN1#+, Jiayi PAN1, Ed ZARON2, David JAY2, Stefan TALKE2
1 Chinese University of Hong Kong, Hong Kong SAR, 2 Portland State University, United States
#Corresponding author: +Presenter

Mean sea level (MSL) exhibits strong seasonal oscillations at annual and semi-annual frequencies in the waters of Southeast Asia in four sub-regions of the Southeast Asian waters; namely, the Malacca Strait (MS), the Gulf of Thailand (GOT), the Java Sea (JS), and the western South China Sea (SCS).  20 tide gauges in Malaysia, Thailand, Indonesia, and Vietnam are analyzed in detail.  Results of monthly harmonic analyses reveal that the major diurnal (K1; O1) and semidiurnal (M2; S2) ocean tides also demonstrate strong seasonal behavior, seen in both amplitude and phase.  The behavior of tidal properties through the year are denoted seasonal tidal anomaly trends (STATs).  Both MSL and tidal properties have strong annual and semi-annual coherences to the western North Pacific monsoon index (WNPMI), indicating that mechanisms associated with monsoons are the likely cause of the tidal variability.  Monsoons are typified by persistent, seasonally reversing wind patterns that influence surface currents, and by seasonal variability in precipitation which modifies freshwater feedbacks of coastal areas. This yields strong seasonal stratification changes in the mainly shallow seas, as well as seasonal modulations in seasonal sea surface height, geostrophic velocities, and in wind-induced Ekman transport, which may explain the observed modifications in the tides, individually or in combination.  Responses of the tides are different in each of the sub-regions, and behavior is also different between diurnal and semidiurnal tides.  A barotropic tide model is employed to investigate observed patterns of tidal variability, and to quantify sensitivities.

OS17-D3-PM2-303A(L3S)-012 (OS17-A001)
Application of a High-Order and Oscillation-Free Advection Scheme in ROMS: HSIMT
Hui WU#+
East China Normal University, China
#Corresponding author: +Presenter

It has been realized for a long time that the numerical solution of tracer advection is a major error source in ocean simulations. MPDATA and 3rd-order, upstream-biased scheme are two major options in ROMS. Although they have been successfully used in many studies, notable overshooting or dissipation were frequently reported especially when simulating the frontal or eddy dynamics. Here in this study we introduced a new advection scheme HSIMT into ROMS. HSIMT is a high-order and finite-volume based geometric advection scheme (Wu and Zhu, 2010, OM), which has shown great advantageous in the studies of the Changjiang River plume. 1D long-term simulation showed that HSIMT can substantially prevent the numerical overshooting even around a sharp/discontinuous front, and at the same time it maintains the gradients very well for both sharp and smooth fronts. While under the same tests, MPDATA and 3rdupstream-biased scheme showed notable dissipation or overshooting or both, and the simulated fronts were often deformed. It was also found that HSIMT is less sensitive to the grid resolutions and time step than other schemes. All these advection schemes were used to simulate the river plume with ROMS. Under different resolutions, HSIMT all simulated a consistent plume pattern with similar volume transport and freshwater transport. On the contrary, the results from other schemes showed significant grid-dependency, and when the resolutions were higher enough they converge to that from HSIMT. 

OS17-D3-PM2-303A(L3S)-013 (OS17-A003)
Seasonal and Inter-Annual Variability of Larval Dispersal and Ambient Currents in the Seto Inland Sea, Japan
Taichi KOSAKO1#+, Yusuke UCHIYAMA2, Satoshi MITARAI3
1 Port and Airport Research Institute, Japan, 2 Kobe University, Japan, 3 Okinawa Institute of Science and Technology Graduate University, Japan
#Corresponding author: +Presenter

Oceanic currents in the Seto Inland Sea (SIS), Japan, are mainly driven by tides, density and sea-surface wind. The fluctuating Kuroshio path situated south of the SIS also plays a significant role in development of the mean circulation in the entire SIS (e.g., Komai et al., 2008). These factors jointly affect dispersal patterns of material, such as larvae, nutrient and toxic substances. Evaluation of effects of the circulation on material transport leads to further elucidation of the marine ecosystem and desirable marine environment in the SIS. In the present study, we quantify larval dispersal by using a double-nested, high-resolution SIS model and a 3-D Lagrangian particle tracking submodel. The computational period is chosen for 8 years since 2007. Primary objectives are to examine 1) seasonal and inter-annual variability of larval dispersal in the entire SIS and 2) effects of each forcing factor around the SIS on the dispersal patterns.

Lagrangian PDFs (e.g., Mitarai et al., 2009) clearly exhibit seasonality of lateral distribution of larval dispersal patterns. In summer, the larvae in several regions are trapped by convergent cyclonic gyres locally-developed around dome-shaped bottom cold water mass, referred to as cold dome (Chang et al., 2009). In winter, southwestward Ekman transport have a prominent influence on dispersal of the larvae released from Iyo Sea in the western part of the SIS, whereas the clockwise circulation associated with northwesterly monsoon rather than the transient Kuroshio path predominantly transports the larvae released from Harima Sea in the eastern part towards the eastern opening, Kii Channel. However, the fluctuating Kuroshio is found to largely affect inter-annual variability of larval dispersal. When the Kuroshio path is located close to Cape Ashizuri, the clockwise mean circulation is enhanced in the entire SIS, promoting eastward transport of larvae in Harima Sea.

OS17-D3-PM2-303A(L3S)-014 (OS17-A004)
Modeling Coastal Dispersal of Wastewater Effluent from Multiple Sources in the Seto Inland Sea
Kobe University, Japan
#Corresponding author: +Presenter

Coastal marginal seas and estuaries are generally dumpsites for waster water from sewage treatment plants (e.g., Uchiyama et al., 2014). The Seto Inland Sea (SIS), Japan, is segmented into several semi-enclosed basins (called “Nada” in Japanese) with complex coastlines and thousands of islands, resulting in partially stratified, complicated tidal and estuarine circulations. Anthropogenic sewage effluent from the densely populated hinterland markedly affects the water quality and marine ecosystem of the SIS (e.g., Uchiyamaet al., 2013). Therefore, social demand has been grown for comprehensive assessment on spatiotemporal variability of sewage dispersal and its influence on the marine environment.

In the present study, we develop a double-nested JCOPE2-ROMS downscaling model for the entire SIS at the horizontal resolution of 600 m. An offline passive tracer model is introduced to simulate 3-D dispersal of arbitrary Eulerian tracers with a point source capability by using the precomputed 3-D current field from the oceanic reanalysis. The tracers are released at a constant flow rate uniformly in the vertical for one year at nine sewage plants chosen from six Nadas on the basis of larger discharge. The results exhibit that bimodal transport patterns occur in the both sides relative to the Bisan Strait (BS) located around the middle of the SIS. On the eastern side, the eastward tracer transport is significantly promoted because of the persistent clockwise circulation in the SIS, enhanced particularly in winter. The tracers remain mostly near the release sites, whereas some portion flows out to the open ocean through the eastern opening. In contrast on the western side of the BS, the discharged effluent is rather spread widely over the entire SIS. The outgoing effluent from the western opening is immediately transported eastward by the Kuroshio and trapped in a mesoscale circulation shed by the Kuroshio. 

OS17-D3-PM2-303A(L3S)-015 (OS17-A005)
A New Perspective on Interannual Sea-Level Variability Around the South China Sea Based on Empirical Mode Decomposition of Tide-Gauge Data
1 Nanyang Technological University, Singapore, 2 Institute of Meteorology, Hydrology and Climate Change, Viet Nam, 3 Earth Observatory of Singapore, Singapore
#Corresponding author: +Presenter

What major forcings govern sea-level variability on an interannual time scale? How does sea level around the South China Sea (SCS) respond to them? Investigations of interannual variability around the SCS have been sparse: the few studies to date have focused on sea level anomalies and sea surface height from ocean models. Here, we use sea-level records from 10 tide gauges around the SCS to explore the interaction between sea level and three major forcings in the region: El Niño-Southern Oscillation (ENSO), monsoons, and oceanic dynamics (via Luzon Strait Transport). To extract the interannual mode, we applied Empirical Mode Decomposition (EMD), a new and robust method to decompose tide-gauge data into time-dependent frequencies, from which we analyze modes with ~2-7 year periods.

Our results show that while the role of oceanic volume transport is minor, interannual sea-level variations are significantly impacted by ENSO. However, in contrast to other studies, our analyses reveal that ENSO signals are dominant only in the southern and central SCS (correlations of ~0.5-0.8). In the northern and western SCS, sea level is more clearly influenced by winter wind stress, with the exceptions of the Gulf of Tonkin and the Gulf of Thailand, where basin geometry and local geography play a role. Sea level in the SCS correlates more highly with the winter monsoon than the summer monsoon, indicating the relative strength of the winter monsoon across the SCS. Notably, this correlation is more evident since the mid-2000s, which may reflect the recent amplification of the East Asian Winter Monsoon.

Our study confirms that EMD is capable of accurately capturing the interannual mode from sea-level records and that the power of climate and ocean forcings on tide gauges is non-uniform and site specific. This challenges regional generalizations for future sea-level planning.

Poster Presentations

  OS17-D4-PM2-P-016 (OS17-A002)
The Response of Phytoplankton Growth to the Physical Processes in Changjiang Estuary and Min-Zhe Coastal Waters
Yihe WANG+, Hui WU#
East China Normal University, China
#Corresponding author: +Presenter

The Hydrodynamics condition in the Changjiang Estuary and Min-Zhe coastal waters is complex and varies seasonally. The key physical processes such as Changjiang diluted water and the seasonal shelf circulation and wind jointly influence the distribution of temperature and nutrient as well as the characteristics of current, which further influences the marine primary productivity. For all this, based on the already built high-resolution, three-dimensional, physics-biogeochemistry coupling numerical model that considers multiple key physical processes such as the runoff, tide, shelf circulation and seasonal wind, this study simulated the growth process of two kinds of phytoplankton including diatoms and dinoflagellates, and furthermore, the study analyzed the influences of those key physical processes on the spatial and temporal distribution of the phytoplankton biomass.

The growth of phytoplankton is mainly controlled by the temperature, light intensity and nutrient concentration. In this study, through analyzing the characteristics of temperature, light condition and nutrient distribution in the Changjiang Estuary and Min-Zhe coastal waters during the time from April to September, the spatial and temporal distribution of two kinds of phytoplankton including diatoms and dinoflagellates is given. Furthermore, by setting numerical trials changing the dynamic conditions to analyze the variation of temperature and nutrient concentration caused by the various key physical processes changes, the biomass variation of two kinds of phytoplankton including diatoms and dinoflagellates is given.
  OS17-D4-PM2-P-017 (OS17-A007)
Intraseasonal Variability and Its Impact on the Chlorophyll Distribution Around Sunda Shelf
Tengfei XU+, Zexun WEI#, Shujiang LI
State Oceanic Administration, China
#Corresponding author: +Presenter

Sunda Strait is the outflow strait of the South China Sea branch of the Pacific to Indian Ocean Throughflow. The annual mean volume transport through Sunda Strait is around 0.25 Sv from the Java Sea to the eastern Indian Ocean, only 2.5% of the Indoensian Throughflow, thus has been ignored by previous investigations. However, the Nutrient concentrations are found highly related to the inflow/outflow through the Sunda Strait. Particularly, our observation shows significant intraseaonal variability at period around 30~40 days in Sunda Strait, which is forced by local zonal wind in combination with intraseasonal Kelvin waves that derived from equatorial Indian Ocean. The mechanism of intraseasonal variability in Sunda Strait is found different from that in Lombok Strait. The Lombok intraseasonal variability is identified as penetrated intraseasonal Kelvin waves, which propagating northward to arrive at Makassar Strait. In comparison, the intraseasonal Kelvin waves leap over Sunda Strait, rather than penetrate into the strait. However, the eastward propation of these Kelvin waves is able to induce sea level anomalies south of Sunda Strait, favoring strengthen or flatten the sea level gradient between the Java Sea and the Indian Ocean. This sea level gradient, together with the impact of onshore or offshore transport forced by local wind, drives the intraseasonal variability of along channel flow in Sunda Strait. Analyses also show significant change of chlorophyll concentration around Sunda Strait during the intraseasonal variability enents.

  OS17-D4-PM2-P-018 (OS17-A009)
T/S Vertical Structure Under the Influence of Oceanic Eddies in the Kuroshio Extension Region
Wenjin SUN1#+, Changming DONG2,3, Ruyun WANG1
1 HoHai university, China, 2 Nanjing University of Information Science & Technology, China, 3 University of California, Los Angeles, United States
#Corresponding author: +Presenter

Based on an oceanic eddy data set collected from the altimetry sea surface height anomalies and Argo vertical profiles collocated within detected eddy areas, the temperature, salinity, potential density, mixed layer depths (MLD) and buoyant frequency in the Kuroshio Extension (KE) region under the influence of eddies are investigated.We examined those physical parameters response to 56728 oceanic eddies in the KE region during the period of 1999--2013. The MLD has significant seasonal variation. Mean vertical structures of temperature, salinity, geostrophic current of the composite eddies are estimated by analyzing Argo profile data collocated in altimeter-detected eddies. The composite analysis shows that eddy-induced ocean variations are mainly confined in the upper 800 dbar. In the eddy core, CE (AC) could induce a cooling (warming) of 1.5℃ (2℃) between 250 and 450 dbar, maximum positive (negative) salinity varies of 0.1 (0.1) in the upper 400 (450) dbar and maximum positive (negative) potential density varies of 0.25 (0.2) kg/m3 in the upper 400 (450) dbar. The CE (AC) can lead an enhance (reduce) of buoyancy frequency at the up ocean, while the depth more than about 400 meter the influence will be weaker and can be neglect.

  OS17-D4-PM2-P-019 (OS17-A010)
A Simulation of Flow Pass the Deep Water Seamount: The Caiwei Seamount in the Northwest Pacific
Xingliang JIANG1#+, Changming DONG1,2, Chunsheng WANG3, Dongfeng XU3
1 Nanjing University of Information Science & Technology, China, 2 University of California, Los Angeles, United States, 3 State Oceanic Administration, China
#Corresponding author: +Presenter

The deep water seamount, Caiwei, which is located in the northwest Pacific Ocean has extensively been investigated by the China Ocean Mineral Resource R&D Association and temperature, salinity and currents were measured. In this study, we employ the Regional Ocean Modeling System (ROMS) to simulate the flow passing the Caiwei Seamount for a field experiment period 2012 – 2014. The comparison of the simulation results with the observational data shows that the ROMS reproduces the temperature and salinity vertical profiles generally. The model also reveals a clockwise gyre around the seamount in the bottom layer of the ocean. The momentum balance around the seamount are analyzed and it is found that nonlinear terms are important at the edge of seamount but the geostrophic balance is dominant in the other areas.

  OS17-D4-PM2-P-020 (OS17-A011)
Chlorophyll Rings in Oceanic Eddies in the North Pacific Ocean
Guangjun XU1,2#+, Changming DONG1,3, Jinsong YANG2, Yu LIU1
1 Nanjing University of Information Science & Technology, China, 2 State Oceanic Administration, China, 3 University of California, Los Angeles, United States
#Corresponding author: +Presenter

Eight years (2003 - 2010) of satellite-measured sea level anomalies (MSLA) and chlorophyll concentration in the North Pacific are applied to investigate the high chlorophyll concentration occurring in the periphery of eddies, called "Chlorophyll Rings". 5,365 cyclonic eddies and 7,078 anticyclonic eddies with distinct chlorophyll characteristics are identified. In spatial and temporal distribution, cyclonic and anticyclonic eddies have similar seasonal variations: more in March, September and October; "Chlorophyll Rings" more appear in both east and west coasts of the Pacific and the extension of Kuroshio. Using Argo data and surface drifters, we find that upwelling is presented in the periphery of anticyclonic eddies, which brings nutrient-rich water upwards into the euphotic zone. During an eddy life period, chlorophyll in the surface water around the eddies could be advected to the periphery of eddies.

  OS17-D4-PM2-P-021 (OS17-A013)
Mass Transport Induced by Coastal Trapped Waves Along the Coast of China Seas
Lin JIANG1#+, Changming DONG1,2
1 Nanjing University of Information Science & Technology, China, 2 University of California, Los Angeles, United States
#Corresponding author: +Presenter

Coastal trapped waves (CTWs) refer to a group of low frequency waves  along an coastal area. Theoretically, the barotropic CTWs can induce the mean Lagrangian transport even with weak friction. The mean Lagrangian transport can be subdivided into a Stokes drift and a mean Eulerian drift. Because of the shallow and broad shelves in the China Seas, the rigid lid approximation used in the analytical solution from the literature is not applicable. We relax the approximation in the CTWs theory for the China Seas. Using idealized bottom topography and other realistic physical parameters for CTWs along the coast of China seas, we calculate the mean Lagrangian transport induced by the CTW along the coast of China Seas. 

  OS17-D4-PM2-P-022 (OS17-A015)
Numerical Study of Multiple-Scale Physical Processes in the East China Sea
Yu LIU1#+, Changming DONG1,2, Yang YU1
1 Nanjing University of Information Science & Technology, China, 2 University of California, Los Angeles, United States
#Corresponding author: +Presenter

In this study, we employ the Regional Oceanic Model System (ROMS) to simulate the oceanic circulation in the East China Sea (ECS) with a high resolution. The model is forced by fully dynamic forcing, including atmospheric momentum, heat and freshwater fluxes at the sea surface, tidal forcing and main river runoffs. The numerical solution is evaluated against observational data. Using the high-resolution product, we investigate the multiple-scale processes in the ECS: interannual, seasonal, intraseasonal (eddy) scales. The Kuroshio effect on the circulation is examined. The water exchange between the Kuroshio and shelf water is examined. The river runoff impacts on the circulation is also discussed.

  OS17-D4-PM2-P-023 (OS17-A016)
Global Ocean Wave Variation During the Last 23 Years (1993-2015)
Yuhan CAO1#+, Changming DONG1,2, Jin WANG1
1 Nanjing University of Information Science & Technology, China, 2 University of California, Los Angeles, United States
#Corresponding author: +Presenter

The trend of global significant wave height (SWH) from the year 1993 to 2015 is calculated using a merged data from six altimeters and in-situ data sets from the National Data Buoy Center(NDBC). Results show that the averaged SWHs at high latitude in the Pacific Ocean , the North-East Atlantic Ocean and the Southern Indian Ocean have a downward trend using linear fitting method. Further, using empirical orthogonal function (EOF) and moving average filtering methods, the annual and seasonal variations of the SWH are examined and it is found that different variations between the first and second decades are presented. The dominant modes of the wave and the wind  have similar characteristic.

  OS17-D4-PM2-P-024 (OS17-A018)
Large Eddy Simulation of a Hydrothermal Plume
Gao XIAOQIAN1,2#+, Changming DONG1,3, Liang JUNHONG4, Li GUOJING5, Chujin LIANG2, Jinsong YANG2
1 Nanjing University of Information Science & Technology, China, 2 State Oceanic Administration, China, 3 University of California, Los Angeles, United States, 4 Louisiana State University, United States, 5 South China Sea Institute of Oceanology of Chinese Academy of Sciences, China
#Corresponding author: +Presenter

Hydrothermal plume is one of major phenomena of convection instability in ocean which  induces strong exchanges of heat and momentum with ambient seawater. To better understand hydrothermal plumes we use Large eddy simulation (LES) to study a hydrothermal plume. LES combine advantage and avoid disadvantage of Direct Numerical Simulation (DNS) and Reynolds-averaged Navier-Stokes Simulation (RANS) by dealing with large scales and small scales separately. We conduct a series of numerical experiments to examine the sensitivity of the hydrothermal plume to the parameters of the vent and oceanic hydrographic condition. We further compare the numerical results with observed data from a mooring system in the southern Indian ocean, which is located at 100 meters away from a hydrothermal vent.

  OS17-D4-PM2-P-025 (OS17-A019)
A Model Study for the River Plume of Jiulong Estuary in the Wet Season of 2015
Chao GU1+, Fanghua XU1#, Peng CHENG2, Wei ZHOU3
1 Tsinghua University, China, 2 Xiamen University, China, 3 Beijing Climate Center, China
#Corresponding author: +Presenter

Jiulong River located in the Southeast of China is one of the largest rivers entering the Taiwan Strait. The estuarine circulation is generally dominated by semidiurnal tides. In wet seasons, the enhanced river runoff potentially exerts large impact on the longitudinal and lateral circulations in the estuary. To study the influence of river plume on estuary dynamics in wet seasons, we configure a three-dimensional baroclinic model in the wet season of 2015 using the Regional Ocean Modeling System (ROMS). It is forced by realistic river discharge, tides, winds, and surface heat flux and freshwater flux. The hindcast model results are compared well with in-situ measurements, including temperature, salinity, and velocity profiles. Temporal and spatial variations in stratification induced by spring-neap tidal cycles and river runoff are quantitatively consistent with observations. The influence of the river plume on the estuarine dynamics is investigated. On one hand, the river plume spreading tends to stabilize the water column, and on the other hand, the plume spreading is a competition between the lateral pressure gradient and Coriolis forces. 

  OS17-D4-PM2-P-026 (OS17-A020)
Variability of Circulation in the Pearl River Estuary: Observation and FVCOM Modeling
Wenfeng LAI#+, Jiayi PAN
Chinese University of Hong Kong, Hong Kong SAR
#Corresponding author: +Presenter

A cruise measurement was implemented in 3-11 May 2014 in the Pearl River estuary and the plume area to explore the estuary circulation and dynamical properties. The ADCP data show that the flood tide causes divergence in the deep channel in the cross estuary direction, while the ebb tide causes convergence. The unstructured grid finite-volume coastal ocean model (FVCOM) with higher spatial resolution is implemented to explore details of the variability of circulations in the Pearl River Estuary, validated by cruise observations and tidal gauge seal level data. Modeling results suggest that the residual surface currents flow seaward and the bottom current flow landward due to the density gradients effects. Under the northeasterly wind, the stratification is weak and the plume turns westward along the coast with an anti-cyclonic bulge, enhancing the seawater intrusion more inside in the estuary, whereas under the southwesterly wind, the plume water spreads eastward, thins, and displays a density gradient current structure that enhances the stratification. With only freshwater discharge forcing, there are the sub-tidal lateral circulations with convergence at the surface and divergence near the bottom of the deep channel. Combined with the tidal effect, lateral circulation is clockwise in the center of the deep channel. Under the northeasterly wind, there is a westward lateral flow at the surface and eastward at the bottom, whereas the lateral circulation is in the opposite direction under the southwesterly wind. The cross-estuary momentum analysis based on the modeling suggests that one main mechanism driving the secondary flow in PRE is Ekman forcing, which represents a dynamical balance between friction and the Coriolis acceleration. The other one is cross-channel baroclinic pressure gradients that arise from differential advection of the longitudinal density gradient. The magnitude of the momentum terms of the experiments considering the tidal effect is ten times larger than non-tidal effect experiments. The northeasterly wind strengthens the nonlinear advection effect more and the southwesterly wind strengthens the friction of the ocean surface.

  OS17-D4-PM2-P-027 (OS17-A023)
Oceanic Eddy Statistical Comparison Using Multiple Observational Data in the Kuroshio Extension Region
JinLin JI1+, Changming DONG1,2, Biao ZHANG1#, Yu LIU1
1 Nanjing University of Information Science & Technology, China, 2 University of California, Los Angeles, United States
#Corresponding author: +Presenter

Eddy characteristics derived from different data resources are compared: sea surface temperature (SST), sea surface height anomaly (SSHA) and surface drifter trajectories. The comparison suggests that the eddy statistical characteristics are different using different variables to delineate eddies, but they show the similar trend. Based on the comparison, abnormal eddies with warm (cold) core but counter-clockwise (clockwise) rotation are found in the KE region. 

  OS17-D4-PM2-P-028 (OS17-A024)
Coastal-Trapped Waves by Local Wind on a Small Bay
Efrain MATEOS#+
Instituto Mexicano de Tecnología del Agua, Mexico
#Corresponding author: +Presenter

Sea level, temperature and velocities fields, from numerical model, were analyzed to study the generation of coastal-trapped waves (CTW) on Todos Santos Bay, Mexico. The model included the California Current System and synoptic winds, which main directions are towards the equator. The wind causes a net southward water transport. In consequence, a bulge of warm water is formed at the south of the bay. This bulge of water is released every four to five days as internal CTW. These waves travel to the north. The CTW on the bay can explain the three or four day velocity variability found in previous studies.

  OS17-D4-PM2-P-029 (OS17-A028)
Different Transport Mechanisms Between Cyclones and Anticylones in the South China Sea with Ocean Modeling
Xiayan LIN1#+, Changming DONG2,3, Dake CHEN1, Yu LIU2
1 State Oceanic Administration, China, 2 Nanjing University of Information Science & Technology, China, 3 University of California, Los Angeles, United States
#Corresponding author: +Presenter

Eddies play a very important role in the water mass, energy, biogeochemical, heat transport.To better understand the mechanisms in the eddy-driven transport, we set up two ideal eddies (one for cyclone, the other is anticyclone) to study the different processes of these two eddies during their life period. In a Lagrangian frame,an individual particle is released at every grid within eddy's boundary. Through tracking the particles, we find that the anticyclonic eddy has better transport ability and better conservation than the cyclonic eddy with particles kept near its boundary and leak outside the boundary. We apply the finding to the numerical results from realistic numerical experiments in the South China Sea to interpret eddy-driven transport.

  OS17-D4-PM2-P-030 (OS17-A032)
Wave Climatological Analysis in the East China Sea
Jin WANG1#+, Changming DONG1,2, Yuhan CAO1
1 Nanjing University of Information Science & Technology, China, 2 University of California, Los Angeles, United States
#Corresponding author: +Presenter

The ERA-Interim dataset from ECMWF (European Centre for Medium-Range Weather Forecasts) are used to study the wave and wind climate in the East China Sea (ECS).

The temporal and spatial variablities in the wave and wind fields on multiple scales from the intraseasonal to decadal are discussed in detail.

The results show that the wave height and the wind speed are highly correlated, especially in winter. For interannual and decadal scale, the wind and wave in the ECS is strongly influenced by the ENSO and PDO with the negative correlation. The trends of the mean wave height and wind speed are studied. Wind speeds increase by 0.005-0.015ms-1a-1 and wave heights by 0.005-0.007ma-1 in most of the ECS during the 36 years from 1979-2014.The regions of the maximum increasing slopes in both wave height and wind speed are located just to the northeast of Taiwan.

It can also be noted that the wind increases along the mean path of the Kuroshio current, which is guided by the Ryukyu islands. The influence of typhoon on the extreme wave and wind trends is also studied. The results show that the trends during typhoon and 90-th percentile have similar spatial distributions, especially for the wave height trend. The regions of the maximum increasing slop of wave height and wind speed are located just to the northeast of Taiwan.

The maximum increasing rates of both wave height during typhoon and 90-th percentile wave height are 0.01ma-1. The maximum increasing rates of wind speed are 0.03ms-1a-1, 0.02ms-1a-1 respectively, which are slightly different between the two. So typhoons could be the main reason for the extreme wave in the ECS.

  OS17-D4-PM2-P-031 (OS17-A034)
Numerical Study on the Bottom Branch of the Yellow Sea Warm Current
Junchuan SUN1#+, Zexun WEI1, Dezhou YANG2, Baoshu YIN2
1 State Oceanic Administration, China, 2 Chinese Academy of Sciences, China
#Corresponding author: +Presenter

The most noticeable hydrographic feature in the Yellow Sea in winter is the presence of warm and salty water mass along the Yellow Sea Trough (YST), which suggests the existence of Yellow Sea Warm Current (YSWC). Previous studies have shown that the YSWC flows along the western side of the YST, while the circulation in the deep YST remains unknown. In this paper, the circulation in the deep YST was carefully examined by numerical simulations based on the Regional Ocean Modeling System (ROMS) together with observations. The historical observation data and model results indicate the presence of a bottom branch of the YSWC which wanders northwestward along the YST in winter. Model results demonstrate that the bottom branch of the YSWC is driven by the northerly wind and the strength of the northerly wind determines the velocity of the bottom branch of the YSWC. The bottom branch of the YSWC flows over several depressions on the seabed and its pathway is S-shaped and leaning to the west due to conservation of potential vorticity. Numerical experiments also reveal that the bottom friction has important influence on the two branches of the YSWC. The bottom branch of the YSWC becomes rather weak when the bottom friction parameter is small. With the increase of the bottom friction parameter, the west branch of YSWC becomes weaker while the bottom branch of the YSWC becomes stronger.

  OS17-D4-PM2-P-032 (OS17-A039)
Spatial and Temporal Variability of Sea Surface Salinity in South China Sea
Yuanyuan FU#+, Xuhua CHENG
South China Sea Institute of Oceanology, China
#Corresponding author: +Presenter

Sea surface salinity(SSS) from situ hydrographic data reveals a freshening trend in SSS in the South China Sea (SCS) during 2004- 2012. Such freshening is also found in the OFES output (ocean general circulation model for the Earth Simulator) and UK met office EN4 objective analyses during 1993-2012. In OFES data, a remarkable freshening is located in the west of Luzon Island. The salinity budget analysis in the upper layer indicates that both the fresh water forcing and horizontal salinity advection in the SCS contribute to the negative trend of SSS in the SCS. In the west of Luzon Island, the excessive precipitation accounted for the decrease of SSS to a great extent, which is associated with the strengthening trend of Walker Circulation. Unlike to the surface freshening, the subsurface salinity increased during 1993-2012, which is related to the intrusion of saltier water from Sulu Sea via Mindoro Strait.

  OS17-D4-PM2-P-033 (OS17-A043)
Effects of Ocean Mesoscale Eddy on Atmosphere
Haixia SHAN#+
Nanjing University of Information Science &Technology, China
#Corresponding author: +Presenter

Atmospheric response to the mesoscale eddy is one of hot topics in the study of mesoscale air-sea interaction, the satellite observations indicated that oceanic mesoscale eddies can leave mesoscale imprints on surface wind, cloudiness and precipitation patterns. What’s more, atmospheric responses to these oceanic eddies are not confined in the marine atmospheric boundary layer (MABL). Although a number of physical mechanisms have proposed, but there is no clear consensus on the potential mechanisms, it still need to further strengthen the understanding of the mechanism of the atmospheric response to the ocean mesoscale eddy. The published literatures show that most studies still remain in the stage of data analysis, this study investigates the atmospheric response to SST anomalies associated with mesoscale oceanic eddies with the Weather Research and Forecasting (WRF) in an idealized, motionless, horizontally homogeneous, and an f-plane assumption. Through a series of sensitivity tests, this project aims to obtain the quantitative relationship of between the mesoscale eddy and the atmospheric variables and study the effects of different atmospheric condition and ocean mesoscale eddy feature on the atmospheric response to the mesoscale eddy. The physical mechanism of ocean mesoscale eddy modulate its dynamic and thermodynamic structure in the atmospheric boundary layer is investigated as well.

  OS17-D4-PM2-P-034 (OS17-A048)
The Coupled Estuarine-Shelf Response in the Flooding Season: A Case Study in the Northern South China Sea
Bo HONG1#+, Hongzhou XU2
1 South China University of Technology, China, 2 Chinese Academy of Sciences, China
#Corresponding author: +Presenter

The coupled interactions between Pearl River Estuary and adjacent coastal ocean in the northern South China Sea are investigated to reveal the responses of the system to the flooding. The flow field and subsequent transport pathways of material exchange between the estuary and shelf are important for understanding the related dynamic mechanism . Analyses of the data from a mooring station facilitate the correlation analyses between the flow field and the forcing field. A three dimensional model was used to reproduce the observed event, which allows schematic analyses on the coupled estuarine-shelf response. The effects of river discharge, wind forcing, and tide are estimated. The results indicate that the transport across the frontal area are fluctuated by wind forcing. Synoptic events are selected to reveal the contribution of each forcing factors. As demonstrated in this study, monitoring and mapping of the transport in this coupled system during a range of environmental conditions will improve valuable insights on the temporal and spatial variability of key parameters that are crucial to the ecological system.