Aerosol-induced changes of convective clouds observed from ground-based observations and CloudSat/CALIPSO

Description

Aerosols have strong impacts on deep convective clouds and associated precipitation through complex microphysical or thermodynamic effects. Using 10-year ground-based observations, we show that warm base mixed-phase clouds in summer are strongly invigorated by aerosols, while this effect does not exist for shallow warm clouds. This finding is further confirmed by using a large ensemble of satellite data acquired by the Moderate Resolution Imaging Spectroradiometer onboard the Earth Observing System’s Aqua platform, the CloudSat cloud profiling radar, and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite over the tropical regions. We identified two distinct responses of clouds and precipitation to increases in aerosol loading. Cloud-top temperatures decrease significantly with increasing aerosol index (AI) over oceans and aerosol optical depth (AOT) over land for mixed-phase clouds with warm cloud bases; no significant changes were found for liquid clouds. The distinct responses are explained by two mechanisms, namely, the aerosol invigoration effect and the microphysical effect. Aerosols can significantly invigorate convection mainly through ice processes, while precipitation from liquid clouds is suppressed through aerosol microphysical processes. Precipitation rates are found to increase with AI for mixed-phase clouds, but decrease for liquid clouds, suggesting that the dominant effect differs for the two types of clouds. These effects change the overall distribution of precipitation rates, leading to more or heavier rains in dirty environments than in cleaner ones.