Dominant role by vertical wind shear in regulating aerosol effectson deep convective clouds

摘要

Aerosol-cloud interaction is recognized as one of the key factors influencing cloudproperties and precipitation regimes across local, regional, and global scales and remainsone of the largest uncertainties in understanding and projecting future climate changes.Deep convective clouds (DCCs) play a crucial role in the general circulation, energybalance, and hydrological cycle of our climate system. The complex aerosol-DCCinteractions continue to be puzzling as more "aerosol effects" unfold, and systematicassessment of such effects is lacking. Here we systematically assess the aerosol effects onisolated DCCs based on cloud-resolving model simulations with spectral bin cloudmicrophysics. We find a dominant role of vertical wind shear in regulating aerosol effectson isolated DCCs, i.e., vertical wind shear qualitatively determines whether aerosolssuppress or enhance convective strength. Increasing aerosols always suppressesconvection under strong wind shear and invigorates convection under weak wind shearuntil this effect saturates at an optimal aerosol loading. We also found that the decreasingrate of convective strength is greater in the humid air than that in the dry air when windshear is strong. Our findings may resolve some of the seemingly contradictory resultsamong past studies by considering the dominant effect of wind shear. Our results canprovide the insights to better parameterize aerosol effects on convection by adding thefactor of wind shear to the entrainment term, which could reduce uncertainties associatedwith aerosol effects on climate forcing.