A Modeling Study Of The Responses Of East China Sea Cold Eddy To Interdecadal Variation Of East Asian Monsoon And Kuroshio

The mesoscale eddy phenomenon in the ocean has got more attention since the1970’s. A lot of studies focused on the cold eddy which locates at the continental shelfin the north of the East China Sea (ECS) were conducted. The ocean environment ofthe ECS was largely influenced by the East Asian monsoon and the Kuroshio. It iswell known that the East Asian climate regime has changed experiencing a significantclimatic jump about1976/1977, whereas the variance of the cold eddy of the ECSbefore and atfer the climate jump did not attach enough importance. In this paper,high resolution oceanic and climatic reanalysis data such as SODA5CORA5COADSand CORE is used to study the trend of the oceanographic elements such as seatemperatures and currents of the ECS in recent decades and the relation between thetrend of oceanographic elements and the cold eddy. The high resolution regionalocean model constructed based on ROMS was applied to study the response of thecold eddy to the climate jump of the East Asian monsoon and Kuroshio before andatfer1976/1977. The main conclusions are listed below:1.Atfer the climate jump, the wind stress over the ECS weakened both inwinter and summer, and the heat transported to the ECS by Kuroshio is enhanced by8%and8.5%, respectively.2.The numerical experiment showed that, atfer the climate jump of the Asianmonsoon at1976/1977, the cold eddy is enhanced in summer and slightly weakenedin winter. Atfer the climate jump of the summer monsoon, the off-sea bifurcation ofthe Taiwan warm current and the Yellow sea warm current that located at thesouthwest side of Cheju Island is strengthened, enhancing the cyclonic current at thecold eddy region, which tends to strengthen the cold eddy in summer. Atfer theclimate jump of the winter monsoon, the Yellow sea warm current that located at thesouthwest side of Cheju Island is weakened and an anti-cyclonic current anomaly wasappeared, which favors the cold eddy weakened in winter.3.Otherwise, the model diagnostic result indicates that, atfer the climate jumpof the heat transported to the ECS by Kuroshio at1976/1977, the cold eddy issignificantly strengthened in summer. And the low temperature in summer at thecenter of the cold eddy is explicitly strengthened. Differed rfom that in summer, thecold eddy has little change in winter. As the Taiwan warm current is enhanced by theclimate change of Kuroshio in summer, the anticyclone of the cold eddy strengthened and the temperature of the center of the cold eddy reduced, furthermore, with theimpaction of the strengthened Taiwan warm current, the location of the cold eddymoved northward. While in winter, the cold eddy is influenced obviously by theYellow sea warm current. The climate jump of the Kuroshio has little effect on Yellowsea warm current. Besides, the strong mixing caused by winter monsoon weakens theinfluence of the heat transported to the ECS by Kuroshio. So the cold eddy has littlechange in winter.4. Analysis of the SODA shows that: atfer the climate jump at1976/1977, insummer the cold eddy is strengthened as in the center of the cold eddy thetemperature is decreased and the salinity is increased, whereas the cyclonic current isenhanced. In winter the temperature of the center of the cold eddy is decreasedslightly and the cyclonic current is weakened significantly, which shows that the coldeddy tends to getting weakened. Analysis of both the SODA and model result showsthat: before and atfer the climate jump at1976/1977, there is obvious inter-decadalvariability of the cold eddy of the East China Sea and the Asian monsoon andKuroshio are the main influencing factors.