Reversal Asymmetry of Rainfall Change Over the Indian Ocean During the Radiative Forcing Increase and Stabilization

The rainfall responses over the Indian Ocean (IO) are investigated based on the Representative Concentration Pathways 4.5 (RCP4.5) experiments of 13 models, in which the experiments are extended to the year 2300, from the Coupled Model Intercomparison Project Phase 5 (CMIP5). During the radiative forcing (RF) increase, the rainfall pattern displays northwest-southeast dipole asymmetry. After RF stabilization, rainfall increases over the southern IO and decreases over the northern IO where is a wet region in climatology. Diagnostic analysis demonstrates that both the changes in atmospheric circulation (dynamic component) and the moisture increase (thermodynamic component) play a key role in determining this rainfall dipole during RF increase, but the effect of the latter is reduced after RF stabilization. The responses of rainfall, sea surface temperature (SST) and atmospheric circulation are well coupled during the two periods: (a) the anomalous circulation affects the rainfall change by transporting abundant moisture to maintain the energy balance, with easterlies (northerlies) in RF increase (stabilization); and (b) in turn, heat released by the SST warming further induces the circulation change. Furthermore, during RF increase, the attribute of SST pattern is mainly led by ocean dynamics, especially heat transport due to ocean current changes, while after RF stabilization, it is mainly due to ocean heat transport leading by temperature changes.