渤海冬季环流形成机制动力学分析及数值研究

DYNAMIC ANALYSIS AND NUMERICAL MODELING OF FORMING MECHANISMS OF WINTER CIRCULATIONS IN THE BOHAI SEA

采用涡度方程、海面实测风应力分布和二维数值方法，对渤海冬季环流形成机制进行了研究。结果表明，渤海冬季海面风应力分布东岸大、西岸小，又因海底十分平坦，从而风应力切变形成的负涡度，成为渤海中部及辽东湾海流是顺时外向流动的主要驱动机制。当考虑海面实测风应力分布、潮余流和开边界入流等条件时，用二维数值方法模拟的渤海冬季环流，与实测吻合良好。一系列数值实验进一步表明：上述关于渤海环流形成机制的动力学分析是正确的；潮余流对黄河三角洲外海的北－东北向海流有重要贡献；海峡处北进、南出的流场是由冬季季风与北深、南浅的海底地形共同作用的结果。

With the vorticity equation measured mean surface wind velocity and two-dimensionalnumerical model, forming mechanisms of winter cireulation of the Bohai Sea are presented. Becauseof small horizontal variation of water density in winter and of very plain bottom, the wind stressbecomes the only main acting force to drive the winter cireulation of the Bohai Sea.From Zhang etal's (1983) statistical wind field data of the Bohai Sea it is found that the wind stress in its eastempart is obviously larger than in its westem part in winters. Calculations show that the averagedvorticity of wind stress is about- 0. 67 × 10-7N/ m3 So on the basis of the vorticity equationnegative vorticity of horizontal shearof the wind stress must drive the clockwise cireulation in the center part of the Bohai Sea and inLiaodong Bay: But most of the present numerical models of Bohai Sea winter cireulation, usingconstant wind velocity, produce anticlockwise water movement in its main part which does not agreeat all with measarements. Because these models ignored the above horizontal shear of wind stress.Using two-dimensional numerical model, and taking into account the effects of the measared windstress distribution, tidal current and inflow at the open boundary, the Bohai Sea wither cireulations issuccessfully modeled and obtained current pattern is almost the same as that measured. A series ofnumrical model tests showed that our dynamic analyses of the fonning mechanism of wintercireulations is completely correct; that horizontal shear vorticity really induces the clockwisecireulation in the main part of the Bohai Sea and in the Liaodong bay; that tidal residual currentsmake important contribution to the north-northeastward current in the Yellow River Delta offshore;that the Bohai Strait flow pattem (inflow in northern part outflow in southm part) is induced bythe of winter monsoon and the deep northem and shallow southem bottom topograph in the strait.