Mesoscale Convective Systems Dominate the Energetics of the South Asian Summer Monsoon Onset

The rapid onset of the South Asian summer monsoon (SASM) is featured as an abrupt increase of rainfall and atmospheric column-integrated moist static energy (MSE). Using convection-permitting simulations, a novel cloud tracking technique, and an MSE budget, the relative roles of mesoscale convective systems (MCSs) and non-MCS deep convection in the SASM onset energetics are studied. The analysis shows MCSs greatly contribute to the sudden increases of rainfall, diabatic MSE sources, and the subsequent enhanced export of column-integrated MSE during the rapid onset phase. A “diabatic sources-energy export” plane analysis delineates the different roles of MCSs and non-MCS deep convection. Although deep convection always leads to a net energy export, mesoscale organization of deep convection dominates the convection-associated positive feedbacks that accelerate the energy cycle of the SASM onset. Sensitivity experiment shows that the results are insensitive to the model resolutions.