Interdecadal change in the summer SST-precipitation relationship around the late 1990s over the South China Sea

Abstract

An interdecadal change in the air-sea interaction over the South China Sea (SCS) after the late 1990s has been identified using a local contemporaneous precipitation-sea surface temperature (SST) and precipitation-SST tendency relationship. During 1979–1998, there is a negative precipitation-SST relationship over the SCS, with a larger magnitude over the northeastern SCS (NESCS) than over the southwestern SCS (SWSCS). The remote effect of warmer SST over the tropical Indian Ocean plays a crucial role in a strong anticyclone and suppressed rainfall over the SCS and western North Pacific. Due to greater mixed-layer depth over the SWSCS than over the NESCS, entrainment heat flux makes a larger contribution to a positive precipitation-SST tendency over the SWSCS than over the NESCS. The cloud-radiation effect has a dominant and positive contribution to the SST tendency over the NESCS, whereas it has a negative contribution to SST tendency over the SWSCS. In contrast, the precipitation-SST correlation becomes weakly negative over the NESCS and significantly positive over the SWSCS during 1999–2013. The CESM-CAM5 model demonstrates that cooler SST over the tropical central-eastern Pacific (TCEP) triggers a weak anticyclone, slightly suppressing rainfall over the SCS. The cloud-radiation effect still contributes mostly to a positive SST tendency over the NESCS. Warmer SST over the SWSCS induces an increase in surface evaporation and low-level moisture convergence and causes enhanced rainfall. That offsets the remote effect of TCEP SST and results in a negative precipitation-SST tendency with negative cloud-radiation feedback. The interdecadal change in remote forcing to SCS rainfall around the late 1990s is related to the evolution of TCEP SST anomalies from the preceding winter to summer, which is possibly modulated by the phase of the Pacific Decadal Oscillation.