Aerosol, cloud, and precipitation interactions: A numerical study of the effects of regenerated aerosols on orographic clouds and precipitation

Atmospheric aerosols affect cloud and precipitation features, and further impact the climate system through the interactions between aerosols, clouds, and precipitation. On the other hand, aerosols are modulated by clouds and precipitation. The aerosol particles processed and redistributed by clouds and precipitation affect the subsequent development of clouds and precipitation. The complexities and uncertainties associated with the observational studies on aerosol-cloud-precipitation interactions (ACPI) justify the use of numerical models. However, most numerical studies investigate ACPI without considering the regeneration of aerosol particles from evaporated cloud droplets, which is a real process in clouds. Thus, their results seem to be inconclusive. This study applies a detailed bin microphysics scheme coupled with the Weather Research and Forecasting model (WRF) to investigate the regenerated aerosol effects on orographic clouds and precipitation. Both warm-phase and mixed-phase clouds have been simulated over two 2D idealized bell-shaped mountains. The results showed that (1) the exclusion of aerosol regeneration in the model results in more precipitation on the ground. (2) The cloud and precipitation properties are very sensitive to the size distributions of regenerated aerosols. (3) The riming rates of ice and snow are not sensitive to regenerated aerosols but that of graupel is very sensitive. (4) The ground precipitation of mixed-phase clouds are not as sensitive as that of the warm-phase clouds to regenerated aerosols. (5) The qualitative effects of regenerated aerosols on mixed-phase orographic clouds and precipitation properties do not change with the choices of different ice nucleation parameterizations. (6) The spatial-temporal variabilities of the background aerosol concentration are reduced when regeneration is considered.