The sensitivity of tropical convective precipitation to the direct radiative forcings of black carbon aerosols emitted from major regions

摘要

Previous works have suggested that the direct radiative forcing (DRF) ofblack carbon (BC) aerosols are able to force a significant change intropical convective precipitation ranging from the Pacific and Indian Oceanto the Atlantic Ocean. In this in-depth analysis, the sensitivity of thismodeled effect of BC on tropical convective precipitation to the emissionsof BC from 5 major regions of the world has been examined. In a zonal meanbase, the effect of BC on tropical convective precipitation is a result of adisplacement of ITCZ toward the forcing (warming) hemisphere. However, asubstantial difference exists in this effect associated with BC overdifferent continents. The BC effect on convective precipitation over thetropical Pacific Ocean is found to be most sensitive to the emissions fromCentral and North America due to a persistent presence of BC aerosols fromthese two regions in the lowermost troposphere over the Eastern Pacific. TheBC effect over the tropical Indian and Atlantic Ocean is most sensitive tothe emissions from South as well as East Asia and Africa, respectively.Interestingly, the summation of these individual effects associated withemissions from various regions mostly exceeds their actual combined effectas shown in the model run driven by the global BC emissions, so that theymust offset each other in certain locations and a nonlinearity of this typeof effect is thus defined. It is known that anthropogenic aerosols containmany scattering-dominant constituents that might exert an effect opposite tothat of absorbing BC. The combined aerosol forcing is thus likely differingfrom the BC-only one. Nevertheless, this study along with others of its kindthat isolates the DRF of BC from other forcings provides an insight of thepotentially important climate response to anthropogenic forcingsparticularly related to the unique particulate solar absorption.