Upper-Layer Circulation in the South China Sea*

Upper-layer circulation is investigated by using all available historical temperature profiles combined with climatological temperature–salinity relationships in the South China Sea. Two cyclonic eddies are revealed: one is located east of Vietnam (called the East Vietnam eddy) and the other is off northwest Luzon (called the West Luzon eddy). Both local Ekman pumping and remotely forced basin-scale circulation are important mechanisms controlling these two eddies. The Luzon Strait transport (relative to 400 db) is estimated to be of the order 3.0 Sv (1 Sv = 1 × 106 m3 s−1) in the mean, and has a seasonal cycle dominated by the annual signal, with a maximum (5.3 Sv) in January–February and a minimum (0.2 Sv) in June–July. Pressure gradients are also examined to explore the dynamics of the intrusion of waters from the Pacific into the South China Sea through the Luzon Strait.