Variability of the Observed Deep Western Boundary Current in the South China Sea

Abstract

The existence of a deep western boundary current (DWBC) in the South China Sea (SCS) was verified by direct observations from three current moorings deployed from September 2015 to September 2018. The average current speeds observed in the DWBC were around 1 cm s−1 along the northern boundary and 3 cm s−1 along the western boundary. The DWBC demonstrates significant intraseasonal variability in the 30–120-day-period band, which may come from the variability in the Luzon overflow or the eddies in the deep SCS forced by a stable Luzon overflow. In addition, observations found that this DWBC along the northern boundary can reverse its direction meridionally in the spring. Model results suggest that if the Luzon overflow decreases one-third of its typical transport, this current reversal can occur. This behavior can be explained through “relaxation” theory.