Structural Difference on the Response of Microphysical and Precipitation Processes to Aerosol Perturbation in a Quasi-Stationary Southwest Vortex System

Abstract

Using the WRF coupled with Thompson aerosol-aware microphysics scheme, a quasi-stationary southwest vortex (SWV) precipitation process occurring in the Sichuan Basin is simulated. Based on three experiments with low aerosol concentration background (“Low”), medium aerosol concentration background (“Medium”), and high aerosol concentration background (“High”), the effects of hydrophilic aerosol serving as Cloud Condensation Nuclei (CCN) on microphysical and precipitation processes are investigated. Results indicate the impact of hydrophilic aerosol on clouds and precipitation structure exhibits structural difference. Aerosol increases from “Low” to “Medium”, precipitation in middle circle of SWV decreases, precipitation in outer circle of SWV increases. Because the outer circle of SWV with strong convection competes with the middle circle of SWV for liquid droplets, leading to a reduction in ice-phase particles in middle circle of SWV. In contrast, more ice-phase particles are formed in outer circle of SWV. The increased ice-phase particles melt into raindrops, leading to an increase in precipitation. Aerosol increases from “Medium” to “High”, precipitation in middle circle of SWV increases, precipitation in outer circle of SWV decreases. The size of liquid droplets formed in outer circle of SWV further becomes smaller. This is not conducive to the formation of ice-phase particles, leading to weaker convection, which makes it becomes less competitive. A large number of small cloud droplets in middle circle of SWV are transported above the freezing layer and participate in the formation of ice-phase particles. The released latent heat promotes convective development, resulting in more precipitation.