冬季南海西边界急流的动力机制分析

Dynamic analysis on the winter current over western boundary of the South China Sea

利用高分辨率的无结构网格海洋数值模式FVCOM(Finite Volume Coastal Ocean Model),结合卫星高度计资料,分析了南海冬季西边界急流的三维空间结构特征及其形成与维持的动力机制。研究结果显示,冬季南海西向强化特征显著,存在西边界急流。该急流的水平和垂向结构复杂多变,表层与次表层海流的流场结构、流速与流幅均有较大差异。动力机制分析表明,该西边界急流具有明显的地转流特征,其压强梯度力与科氏力有较好的对应关系;同时,由于风应力、地形及平流效应的影响,西边界急流还具有显著的局地变化特征。进一步的数值实验分析表明,压强梯度力与海面风应力对南海冬季西边界急流的形成与维持起重要作用。其中,压强梯度力的垂向分布特征与西边界急流的三维结构吻合良好;而风应力对南海冬季西边界急流的影响与岸线及地形的分布特征有密切的联系。

The three-dimensional structure of western boundary current of the South China Sea （SCS） in winter is investigated with the unstructured grid, Finite-Volume Coastal Ocean Model （FVCOM） and the altimeter data. The dynamic mechanisms of the current are explored by the numerical experiment and the dynamical diagnose analysis. The modeling results and the altimeter data show that the western boundary current has greater velocity than nearby current, which comes from northern SCS and flows along the 200m isobath towards southwest. It＇s strengthened at the southeast of Hainan Island and forms the south rush flow. The horizontal and vertical structure of western boundary current is complicated and variable. Since the pressure gradient force is associated with the Coriolis force, the western boundary current is generally dominated by the geostrophic currents. On the other hand, the current has local characteristics because of the impact of the winds, topography and the nonlinear advection, etc. Among these factors, the pressure gradient force and winds have the most significant contributions on the formation and evolution of the western boundary current. The distribution of pressure gradient force is agreed with the three-dimensional structure of the current very well. The impact of winds on the current is related to the local topography and the coastline.