South Asian Summer Monsoon Response to Aerosol-Forced Sea Surface Temperatures

Climate models suggest that anthropogenic aerosol-induced drying dominates the historical rainfall changes over the heavily populated South Asian monsoon region. The regional response depends on both the aerosol fast radiative effect and the slow process through sea surface temperature (SST) cooling. Two atmospheric general circulation models, NCAR-CAM5 and GFDL-AM3, are used to investigate the monsoon response to prescribed aerosol-forced SSTs. The total SST is separated into uniform cooling and a spatially varying component characterized by interhemispheric asymmetry. The monsoon rainfall is predominantly controlled by the nonuniform SSTs, in the local Indian Ocean, South, and East China Seas (IO-CSs). The reduced meridional SST gradient in the IO-CSs leads to weakened monsoon circulation, which drives a north-south dipole rainfall change. The latitudinal location of the dipole shows model dependence due to differences in local SSTs and their meridional gradient, which determines the latitudinal location of the meridional overturning circulation responses.