Cloud Top Radiative Cooling Rate Drives Non-Precipitating Stratiform Cloud Responses to Aerosol Concentration

Increases in aerosol concentration are well known to influence the microphysical processes and radiative properties of clouds. By reducing droplet size, an increase in aerosol can lessen collision efficiency and increase liquid water path (LWP) in precipitating clouds or enhance evaporation rate and decrease LWP in non-precipitating clouds. We utilize large eddy simulations to further investigate these aerosol indirect effects in Arctic mixed-phase clouds and find, in agreement with previous studies, precipitating clouds to experience an increase in LWP and non-precipitating clouds a decrease in LWP. Most importantly however, our results reveal a different explanation for why such an LWP decrease occurs in decoupled, non-precipitating clouds. We find enhanced evaporation near cloud top to be driven primarily by a strengthening of maximum radiative cooling rate with aerosol concentration which drives stronger entrainment, an effect that holds true even in clouds that are optically thick.

Automated summary

Increases in aerosol concentration can affect the microphysical processes and radiative properties of clouds, leading to changes in liquid water path (LWP). Precipitating clouds experience an increase in LWP while non-precipitating clouds experience a decrease in LWP. In decoupled, non-precipitating clouds, the decrease in LWP is primarily driven by enhanced evaporation near the cloud top due to a strengthening of maximum radiative cooling rate with aerosol concentration.