南海环流动力机制研究综述

Overview of the South China Sea circulation and its dynamics

南海的环流复杂,但通过近20 a来的研究工作,国内外学者对此已取得了不少的成果.本文就南海环流框架性的问题,综述了有关的文献,认为对南海上层海洋三方面的环流分量的驱动机制已有了初步的认识.这三方面分别是:(1)准季节性风场;(2)黑潮向南海的净输运;(3)黑潮向南海的涡度平流输送.但是对这些驱动的时空变化仍相当不清楚.三者皆增强了南海北部的海盆尺度气旋式环流,其强化的西南向西边界流靠近东沙群岛,建议称为“东沙海流”.没有水文证据显示黑潮水是以分支形式进入南海,其向南海的输运也不可能主要通过中尺度涡过程,具体机制有待研究.每年在南海生成的中尺度涡平均约有10个,风场与沿岸地形所生成的强风应力旋度可能是其主要的驱动机制.作为框架性的认识,也有三方面的工作进行得较少,即:(1)吕宋海峡的上层水交换;(2)南海的中尺度涡生成机制,虽然强风应力旋度及前述的第三种环流驱动机制也有中尺度涡伴生;(3)自吕宋海峡进入的深层水对南海上层海洋环流的影响.

The South China Sea （SCS） has a complex energetic circulation, especially at its northern part. Three major factors contributing to a generally cyclonic gyre in the upper ocean of the northern SCS are identified： （1） monsoonal wind forcing; （2） net water transport into the SCS through the Luzon Strait; （3） vorticity advection from the Kuroshio. The intensified western boundary current of the cyclonic gyre, called the “Dongsha Current” in this paper, flows southwestward next to the shelf south of China. It extends all the way south in winter and reaches central Vietnam in summer. Every year around 10 meso-scale eddies are present in the SCS. Strong wind-stress curl from orographic effects is likely responsible for their generation. Vorticity advection from the Kuroshio can also induce meso-scale eddies. Available hydrographic data do not support the notion that the Kuroshio water enters the South China Sea as a “branch” current, nor primarily as meso-scale eddies. More likely, the Kuroshio water enters the South China Sea principally during the winter monsoon through sub-mesoscale processes confined in the surface layer.