夏季长江冲淡水转向机制的数值试验

利用普林斯顿海洋环流模式(POM)，通过一系列的理想试验，探讨了夏季长江冲淡水的扩展机制。结果表明：(1)倾斜底形是夏季长江冲淡水向东北偏转的一个必要条件；夏季冲淡水向东北偏转是南风、斜压效应和底形的共同作用的结果，其中风应力和底形的相互作用占主导地位；单纯的底形东倾不能使冲淡水向北偏转。平底时，南风和淡水浮力强迫都不能使冲淡水向北偏转。(2)无风时，人海淡水可以在河口附近强迫出一个反气旋涡旋和贴岸南下的狭窄的沿岸流，反气旋涡旋与淡水浮力强迫(斜压效应)有关，南下沿岸流则与质量输入有关；平底时，反气旋涡旋位于河口正东，倾斜底形时，反气旋涡旋向北拉伸，冲淡水的一部分沿岸向北扩展；人海淡水在河口附近强迫出一个闭合的垂直环流圈：上层为离岸流，淡水向外海扩展，约在离岸30—45km处有下降流；低层有高盐水沿海底流向河口，约在离河口。lOkm处与向海的径流相遇，引起上升流。

NUMERICAL STUDY ON THE MECHANISM OF THE EXPANSION OF THE CHANGJIANG RIVER DILUTED WATER IN SUMMER

A series of numerical experiments were conducted using Princeton Ocean Model (POM) to investigate the behavior and mechanism of the expansion of the Changjiang River diluted water on the shelf of the East China Sea The results show that the bottom topography with variable depths is an essential prerequisite in determining the northeastward expansion of the Changjiang River diluted water in summer The turning of the outflow of the Changjiang River in summer is due to the combined effects of the upwelling favorable wind stress,baroclinicity and bottom topography,whereas the interaction between the wind stress and topography is the main cause On the contrary,in the case of flat bottom,neither the upwelling favorable wind nor the buoyancy forcing induced by the outflow freshwater can make the diluted water turn northeastward Further,without wind forcing,the inflow freshwater induces an anticyclonic eddy near the estuary and a southward coastal current; the former is due to the buoyancy forcing ,while the latter is produced by the mass input from the Changjiang River In the case of flat bottom,the anticyclonic eddy is located in the east of the river mouth When the bottom with variable depths is considered,the anticyclonic eddy is stretched northward,and part of the discharged water flows northward The inflow freshwater can produce a closed vertical circulation cell in the estuary: the freshwater flows seaward in the upper layer and the downwelling occurs around 30-45km away from the coastline; the saline water returns in the lower layer,with the occurrence of upwelling when it meets the seaward inflow around 10 km away from the coastline