On the Role of Ocean Dynamics in the Surface Heat Budget of the South China Sea
Tangdong Qu
Abstract
Surface heat budget is examined using historical data in the South China Sea. On the seasonal time scale, the sea surface temperature (SST) is found to be negatively correlated with the mixed layer depth (MLD) in most parts of the basin, that is, SST tends to be higher when MLD is shallower and vice versa. Dynamically, the South China Sea can be partitioned into four smaller areas: one along the continental slope south of China, one off west Luzon, one in the central part of the basin, and one near the coast of Vietnam. Heat budget assessment in these smaller areas indicates that, although surface heat flux is fundamental to the seasonal change of SST, the effect of ocean dynamics is also significant. Advection by Ekman drift is the primary heating process in winter, equivalent to a surface heat flux of 30-80 W m-2 into the ocean, but it has little effect in summer as a result of weaker horizontal temperature gradient. Advection by Ekman pumping is significant in summer but becomes negligible as MLD deepens toward its seasonal maximum in winter. Advection by geostrophic flow is generally weak, except along the continental slope south of China, where convergent currents accomplish a warming advection of about 40 W m-2 in summer. In the central South China Sea, SST reaches its seasonal maximum in May, about 5 months before surface heat flux changes its sign. Ocean dynamics associated with the onset of the southwest monsoon might be the cause of this time difference.
