Effects of Aerosol Solubility and Regeneration on Warm-Phase Orographic Clouds and Precipitation Simulated by a Detailed Bin Microphysical Scheme

This study evaluates the possible impact of aerosol solubility and regeneration on warm-phase orographic clouds and precipitation. The sensitivity evaluation is performed by simulating cloud formation over two identical 2D idealized mountains using a detailed bin microphysical scheme implemented into the Weather Research and Forecasting model (WRF) version 3. The dynamics, thermodynamics, topography, and microphysical pathways were designed to produce precipitating clouds in a linear hydrostatic mountain wave regime. The cloud over the second mountain is affected by regenerated aerosols advected from the cloud over the first mountain. Effects of aerosol solubility and regeneration were investigated with surface relative humidity of 95% and 85% for both clean and polluted background aerosol concentrations. Among the findings are the following: 1) The total number of cloud drops decreases as the aerosol solubility decreases, and the impacts of aerosol solubility on cloud drops and precipitation are more significant in polluted clouds than in clean clouds. 2) Aerosol regeneration increases cloud drops and reduces the precipitation by 2%-80% in clouds over the second mountain. Regenerated aerosol particles replenish one-third to two-thirds of the missing particles when regeneration is not considered. 3) Different size distributions of regenerated aerosol particles have negligible effect on clouds and precipitation except for polluted clouds with high aerosol solubility. 4) When the solubility of initial aerosol particles decreases with an increasing size of aerosol particles, the modified solubility of regenerated aerosol particles increases precipitation over the second mountain.