The Impact of Regenerated Aerosols on the Microphysics of Cumulus Clouds

Abstract Cumulus clouds play a crucial role in the Earth’s energy balance and water cycle. The interactions between aerosols and clouds significantly influence cloud dynamic and microphysical processes, and hence their radiative and rain properties. Aerosol regeneration, the process by which the complete evaporation of droplets releases aerosol particles back to the environment, is an important aspect of this interaction. This study examines the impact of regenerated aerosols on cloud microphysics (through lateral entrainment), using high-resolution simulations of single cumulus clouds under two aerosol regimes (clean and polluted). For each regime, two simulations were conducted: one incorporating an aerosol regeneration scheme and one without. Our results reveal that aerosol regeneration significantly impacts droplet concentrations and size distributions, particularly in the diluted regions of the cloud where evaporation predominantly occurs and regenerated aerosols can be later reactivated into droplets. In clean aerosol conditions, aerosol regeneration significantly reduces surface precipitation, producing only half of the amount compared to the simulation without regeneration. These findings highlight the critical importance of accurately representing aerosol–cloud interaction, particularly aerosol regeneration, in cloud models to better capture their effect on cloud microphysics and precipitation processes.