Role of Air-sea Coupling in the Interannual Variability of the South China Sea Summer Monsoon

Abstract

A possible role of the air-sea coupling in the South China Sea (SCS) summer monsoon variability is studied using a coupled general circulation model (CGCM) and its atmospheric component (AGCM). The 50-year integration of the CGCM well reproduces the summer monsoon variability over SCS, where the precipitation anomaly is positively correlated with the low-level cyclonic circulation anomaly that accompanies enhanced surface westerlies. Negative sea surface temperature (SST) anomaly is found in SCS during the strong monsoon years, indicating the atmospheric driving SST through wind-induced evaporation. The 50-year AGCM run forced by historical SST obtained from the CGCM reveals the monsoon variability amplified by about 50 percent as compared with the CGCM. The absence of the air-sea coupling keeps SST warm in SCS, which increases the local evaporation and precipitation. The enhanced precipitation over SCS may intensify surface westerly over the remote regions, resulting in an increase in the moisture flux convergence that in turn contributes to the positive precipitation anomaly. This result suggests that the air-sea coupling works to stabilize the monsoon and hence suppress the variability via the large-scale moisture transport and the wind-induced local evaporation.