Generation mechanism of the counter-wind South China Sea Warm Current in winter

Abstract

A 22-year (1994–2015) HYbrid Coordinate Ocean Model (HYCOM) global reanalysis is used to study the generation mechanism of the counter-wind characteristic of the South China Sea Warm Current (SCSWC) in winter seasons. Our analysis clearly demonstrates that the counter-wind SCSWC in winter is driven by wind relaxation. An Extended Empirical Orthogonal Function (EEOF) analysis of the hourly Sea Surface Height (SSH) and wind stresses reveals that the most dominant SSH mode is an Ekman mode. When the wind relaxes, the Ekman transport anomaly is offshore and generates a favorable cross-shore SSH slope for the northeastward surface currents over the continental shelf mainly by geostrophic balance. The alongshore pressure gradient force also increases when the wind relaxes, and dominates the weak wind stresses to push the alongshore water northeastwards. We also identify the region south of Taiwan Strait as the origin of the SCSWC, instead of the Hainan Island or Gulf of Tonkin, Vietnam due to the dominant Ekman dynamics.