SURFACE CIRCULATION IN THE SOUTH CHINA SEA

A three-dimensional, primitive-equation model with a free surface is used to simulate the monthly circulation in the South China Sea. The model has a resolution of 0.4 degrees in the horizontal and 21 layers in the vertical in a region from 2 degrees N to 24 degrees N and from 99 degrees E to 124 degrees E. Inflow and outflow in the Kuroshio, through the Taiwan Strait, and between the Sunda Shelf and the Java Sea are prescribed bimonthly. At the sea surface, the model is forced by monthly-averaged climatological winds and temperature and seasonally-averaged salinity. Several important features are reproduced in the model simulation. First, a strong coastal jet is present at the western boundary. The current is southward along the continental margin from China to southern Vietnam in winter. In summer, the current is northward and separates from the coast between 11 degrees N and 14 degrees N. The transition in September begins as a southward undercurrent, which is remotely forced by the northeast monsoon in the northern reaches of the south China Sea. The undercurrent extends to the surface in about a month. Second, inflow through the Luzon Strait from October to February transports the Kuroshio water in the top of 300 m of the water column westward along the continental slope south of China. In summer, eastward flow in the Luzon Strait transports surface water west of Luzon to the region east of Taiwan. Finally, a subsurface current, which is opposite to the surface current, exists over the Sunda Shelf and is driven by a pressure gradient set up by monsoon winds. These simulated currents are in qualitative agreement with the circulation inferred from the available observations.