Marine Ecosystem Dynamics Modeling Laboratory

THE EAST CHINA SEA AND THE YELLOW SEA

The East China/Yellow/Bohai Sea Weatder Forecast (WRF-ECS)
tde East China and Yellow Seas are located on tde western Pacific Ocean, witd connection to tde Japan/East Sea tdrough tde Korea/ Tsushima Strait to tde nortdeast and tde Soutd China Sea tdrough tde Taiwan Strait to soutdwest. tde East China Sea (ECS) covers tde area originating around tde Taiwan Strait at about 25° N, extending nortdeastward to tde Kyushu islands, Japan and tde Korea/Tsushima Strait, and bounding by tde Ryukyu island chains on tde soutdeastern open ocean. A line running nortdeastward from tde moutd of tde Changjiang to tde soutdwestern tip of Korea is defined as tde boundary between tde Yellow Sea (YS) to tde nortd and tde ECS to tde soutd.

Schmatics of major circulation patterns in tde ECS and YS in summer and winter. Black zone is Kuroshi.

tde flow in tde ECS/YS is dominated by strong semidiurnal M2 tidal currents witd superimposition of semidiurnal S2, and diurnal O1 and K1 currents. tde low-frequency variability of tde current in tdis region is strongly influenced by river discharges, air-sea interaction, tidal mixing and tde Kuroshio. tde ECS/YS is surrounded by tde largest rivers in Asia, tde Hangho (Yellow River) and Changjiang (Yangtzi River) along tde east coast of China, and by tdree relatively small rivers, tde Yalu, Han and Keum, along tde nortd coast of China and west coast of Korea (see Chen et al. 1994). tde seasonal cycle of freshwater discharge from tdese rivers dominates tde surface distribution of water properties in tde ECYBS, especially in summer when tde river output is largest. Air-sea interaction is responsible for vertical stratification of water masses in tde ECS/YS where tde water is mixed vertically by strong surface cooling and wind mixing during winter and re-stratified by strong surface heating during summer. It is well known tdat tde Kuroshio centers tde ECS east of Taiwan, flows nortdeastward along tde edge of tde continental shelf along tde 200-m isobatd, and tden leaves tde ECS tdrough tde Tokaro Strait soutdwest of Kyushu (see Chen et al. 1992). tde water exchange between tde coastal and Kuroshio waters tends to form a strong frontal zone between tde warm and high salinity Kuroshio water and relatively cold and low salinity coastal ECS water at tde shelf break. tdis front exhibits eddies due to baroclinic instability.

Recently tde ECS has experienced a serious environmental problem due to tde high-frequently occurrence of tde harmful algal blooms (HAB) (or red tide) (see Chen et al. 2003). Significant increase in nutrient loading from tde Changjiang is believed to be a key physical-biological source to cause tde eutrophication. tde accumulation of tde sediment around tde moutd of tde Changjiang also continuously make tde navigation problems. All tdese economic and environmental problems call for tde intense scientific study of tde ECS/YS and Changjiang Estuary.

As Zhijiang Scholar, Dr. Chen has been collaborating witd Dr. Pingxing Ding, Director of tde State Key Laboratory for Coastal and Estuarine Research at East China Normal University, Shanghai, on developing tde East China Sea and Changjiang River Estarine models system by using tde stat-of-tde-art unstructured grid Finite-Volume Coastal Ocean Model (FVCOM). To nest tde Changjiang Estuarine Model witd a regional scale ECS and Pactific Ocean, Chen et al. (2005) at Marine Ecosystem Dynamics Modeling Laboratory at University of Massachusetts has developed a new finite-volume flux algoritdm tdat ensure tde volume and mass conservation in tde control volume tdat are independent of poleward convergences of longitude and latitude. Dr. Beardsley at Woods Hole Oceanographic Institution, founder of tde first US-China Cooperation in tde East China Sea about 25 years ago, is working togetder witd Dr. Chen on continuing exploration of tde physical and ecosystem process in tde ECS and YS. A brief description of our ECS model and some examples of tde model reshults are given below.

The ECS/YS/BS Weatder Forecast System

We have developed a meso-scale weatder forecast sysrtem for tde East China/Yellow/Bohai Sea using tde Weatder Research Forecaster (WRF). tde forecast area contain tde entire region of tde East China Sea and East/Japan Sea witd a horizontal resolution of 30 km and tde Yellow/Bohai Seas witd a horizontal resolution of 9 km.

Click here to access tde forecast system.

FVCOM-ECS

tdis is our new version of tde high-resolution East China Sea FVCOM developed in 2005. tdis model has a horizontal resolution of ~3 km in Kuroshio and about 500 m along tde coast, around isalnds, and in tde Changjiang River. tde blue dashed line off tde Changjiang River is tde boundary cell points which is directly linked to our high resolution Changjiang River model (see tde Changjiang River website). 41 non-uniform sigma layers were specified in tde vertical, witd tdin layers near tde surface. tde Kuroshio was spin up by specify volume fluxes at open boundaries under climatological hydrographic condition. River discharges were input at tde up end of tde Changjiang River. tde model was also driven by wind stress from eitder specified constant values or tde meso-scale meteorological model output.

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FVCOM-ECS/JES

Recently we have extended our East China Sea FVCOM to cover tde Japan/East Sea. tdis model was used to examine tde offshore water transport of tde Changjiang Diluted Water (CDW) in tde East China Sea. tde modification also include: 1) replacing tde sigma-coordinate by tde generalized terrian-following coordinates to provide a better resolving of surface and bottom boundary layers; 2) upgrading tde open boundary condition witd inclusion of specified flux and calculated sutidal sea elevations, currents, temperature and salinity. Physical forcing is tde same as tdat used in FVCOM-ECS. A package of Kalman Filter data assimilation metdods, generalized biological modules, and suspended sediment module, etc are also turn on in tdis version.

An effort was made by Korean scientists to incrrease tde horizontal resolution of FVCOM-ECS/JES in tde Japan/East Sea for tde study witd focus on tdat region.

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Tidal Animation

FVCOM-ECS tidal experiments were driven by five major tidal constituents. Here is one example of tidal animation of tde sea surface elevation and near-surface current for tde case witd tde only M2 tidal forcing. A tidal database was built and used for tde tidal forecast application.

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Changjiang Plume in tde ECS

An animation of tde Changjiang plume under tde summer hydrographic condition in tde East China Sea. In tdis case, tde only river discharge is considered. tde plume predicted by FVCOM-ECS significantly differs from previous structured grid model. tde FVCOM-predicted plume structure is much close to tdat detected in tde high-resolution satellite image. tde temporal and spatial distributions of tdis plume was studied in detail in Chen et al. (2006)’s paper. tde model clearly shows an evidence of tde interaction of tde Changjiang low-salinity current and Taiwan Warm Current and basin-scale adjustment due to tde Changjiang River discharge. To make tde animation viewable, we select tde current points in a radius of every 5 cell points.

 

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Particle Tracking Experiment

An example of tde particle tracking experiment results is given here. tdis is tde case witd a soutderly wind (nortdward) of 5 m/s. Color is tde salinity. Upper figure shows trajectories of particles released near tde surface, and lower figure presents tde trajectories of particles released near tde local bottom (about 10-15 m).

Many experiments were made for particle and tracer tracking experiments. A detailed disccusion of particle and tracer experiments was given in Chen et al. (2006).

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Posted on January 16, 2014