Impacts of radiative effect of pre-monsoon biomass burning aerosols on atmospheric circulation and rainfall over Southeast Asia and southern China

Biomass burning aerosols (BBA) emitted from Southeast Asia in boreal spring can alter the regional climate via their strong radiative effect. In this study, we have examined the radiative impacts of BBA on the atmospheric circulation and rainfall during the emission season (April–May) using the Weather Research and Forecasting model with chemistry module. Results show that the surface cooling and the atmospheric heating induced by the semi-direct radiative effect of BBA can exert regional heterogeneous influences on precipitation over Southeast Asia and downwind southern China, by disturbing the atmospheric stability, regional circulation and moisture transport. Increased stability (cooling below and warming above) within the planetary boundary layer inhibits local shallow convection and rainfall over mainland Southeast Asia, leading to a build-up of available convective potential energy that favors precipitation downstream in coastal South China. On the other hand, increased solar heating by absorbing aerosols can serve as an anomalous heat source in the low-mid troposphere, inducing a low-level cyclonic wind anomaly and convergence and a mid-level anticyclonic wind anomaly and divergence, along with strong ascending motion reaching the mid-high troposphere. Eventually, the modified stability and regional moisture transport lead to significant redistribution of precipitation. The enhanced (weakened) moist and warm southwesterly wind due to BBA increase (decrease) rainfall over the southern coast (northern inland) of southern China. Extremely, enhanced heavy rain events are found to be associated with an intensified low-level jet stream along coastal South China.