Quantitative study of the interannual variability of South Asian summer monsoon rainfall regulated by SST

Abstract

Most of the rainfall over South Asia occurs from June to September, and its variation is strongly related to the fluctuation of sea surface temperature (SST) on a global scale. In this study, we investigate how and to what degree the interannual variance (IAV) of South Asian summer monsoon (SASM) rainfall is regulated by SST anomalies through comparing the multi-model simulations forced by observed interannual SST variation and climatological SST just with annual cycle. Results indicate that the interannual change in global SST can explain nearly 50% of the IAV of SASM rainfall, in which dynamic process (via atmospheric circulation), instead of thermodynamic process (via water-vapour effect), plays a dominated role. SST influences the IAV of SASM rainfall mainly through changing the lower-and upper-level atmospheric circulations, namely, the large-scale vertical wind shears. Additional sensitivity experiments with the NCAR Community Atmosphere Model show that the effect of tropical Pacific SST (~24.0%) is more important than that of tropical Indian Ocean SST (~15.3%) on regulating the IAV of SASM rainfall.