Numerical Simulation Of Seasonal Changes Of The Circulation And Changjiang Diluted Water In The Yellow Sea And East China Sea

In this paper, making using of the three dimensional ECOM model, which includes monthly averaged data of Changjiang discharge, wind, sun radiation, net heat flux, evaporation, precipitation, circulation and tide from measured data and results of model calculations, to analyze and investigate characters and dynamic mechanisms of the seasonal changes of the circulation and Changjiang diluted water in the Yellow Sea and East China Sea.Including several factors, the circulation numerical experiment in the Yellow Sea and East China Sea reconstructed the Kuroshio, the Taiwan Warm Current, the Tsushima Warm Current, the Yellow Sea Warm Current, coast currents and so on fairly well. The place of the Kuroshio entering into the continental shelf is always at the northeast area of Taiwan. In autumn and winter, the main intrusion of the Kuroshio happens in the surface and mid layers; in spring and summer, the main intrusion happens in the bottom layer. While the surface and mid flows of the Taiwan Warm Current are moving along the shore of Fujian and Zhejiang, their directions turn east obviously for one time. The place where the flow turns east changes seasonally in the surface layer, but it doesn't change in the mid layer. The source of the Tsushima Warm Current will change in the year: in January and February the main source is the flow from the Kuroshio; from March to August, the main source gradually changes from the Kuroshio to mixed water of the flow from the Taiwan strait and the Changjiang diluted water; after August, the main source changes back to be the Kuroshio. From April to August, the Yellow Sea Cold Water Mass appears in the mid and bottom layers, and its highest intensity appears in August. The appearance of Cold Water Mass induces a large-scale cyclone circulation in the center of the Yellow Sea. After September, the Cold Water Mass weakens in the mid and bottom area of the Yellow Sea, and it disappears with the cyclone circulation after November. In the bottom of the Yellow Sea, there is the Yellow Sea Warm Current,which comes from Cheju Island, flowing into Bohai Strait in the whole year. From March to August, the Yellow Sea Warm Current weakens and a part of it flows west while the Yellow Sea Cold Water Mass is enhancing. The source of the Yellow Sea Warm Current in the bottom layer is mixed by water of the Kuroshio and some current from the continental shelf.From January to April, the Changjiang diluted water keeps its south direction along the bank, because of the north wind. From May to August, the direction of the Changjiang diluted water gradually turns to the north, while the wind direction is turning to the south. The Changjiang diluted water can't expand to the north, but only to the northeast, because of the affection of the Yellow Sea Cold Water Mass in summer. For the flux in July is the largest, the Changjiang diluted water can expand farthest to the northeast in July. After September, the wind turns north quickly, which makes the Changjiang diluted water turn south and expand along the shore in a short time.The vertical mix influence of wave weakens while the water depth is increasing. There are no obvious thermocline and halocline in winter, so the vertical mix influence of wave does not affect the main structure of the winter circulation in the Yellow Sea and East China Sea obviously, in spite of its increment of vertical viscosity and diffusivity in the near surface layer. In summer, the vertical mix influence of wave makes the vertical distribution of temperature and salinity in the surface layer almost uniform. It makes the gradient structure horizontal in the surface layer, brings the baroclinic press towards the shore, and blocks Changjiang diluted water expanding northeast. Because of the change of Changjiang diluted water, the structure of surface circulation in the Yellow Sea and East China Sea are affected by the vertical mix influence of wave. But in the realm of deep water, the structure of circulation is not affected obviously.