Coastal jet separation and associated flow variability in the southwest South China Sea

Abstract

A three-dimensional, high-resolution regional ocean model, forced with high-frequency wind stress and heat flux as well as time- and space-dependent lateral fluxes, is utilized to investigate the coastal jet separation and associated variability of circulation in the southwest South China Sea (SSCS). It is found that the circulation and its variability in the SSCS are dominated by the flow fields and eddies associated with the southward and northeastward wind-driven coastal jet separation from the coast of central Vietnam in the winter and summer, respectively. As a result of the coastal jet separation, cyclonic and anticyclonic eddies with strong flow variability are generated in the regions to the southeast of the Vietnam in the winter and to the east off central Vietnam in the summer. The separation of the wind-driven coastal jet is largely associated with the formation of adverse pressure gradient force over the shallow shelf topography around the coastal promontory off central Vietnam, balanced mainly by wind stress in the summer and by both wind stress and nonlinear advection in the winter. In the vorticity balance, a bottom pressure torque, the force exerted on the wind-driven current by the shelf topography, tends to yield an adverse vorticity favorable for the separation of coastal jet. The results suggest that the interaction between wind-driven coastal currents and shelf topography in the nearshore waters plays a crucial role in controlling the separation of the coastal jet.