The effects of aerosol on the growth of hydrometeors in deep convective clouds

Abstract

The impact of aerosol on the development of deep convective clouds and the growth of hydrometeors was investigated using the Weather Research and Forecasting model with a detailed spectral bin microphysics scheme. The simulated cloud top temperature, the vertical profile of moving speed of hydrometeors, and the spatial distributions of precipitation rate were compared with observations from satellite, cloud radar, and weather stations, respectively. The results show that the smaller cloud droplets in the polluted condition have greater mobility with ambient air, which can reach up to 10 km of altitude comparing with 7 km in clean condition, thereby increase the collecting efficiency between ice crystals and supercooled liquid droplets therein. Moreover, ice crystals move slowly around 8 km, thereby facilitating the riming of ice particles by supercooled water to form hailstones. The efficient upward transport of cloud droplets in the convective core area further amplifies this process. Increased aerosol concentration enhances the hail production rate by 2 to 3 orders of magnitude, and results in a 3.48 % increase in effective terminal velocity of hailstone from surface to 4.5 km. The aerosol-induced hail growth effect is stronger over convective cores than that over non-core area. The intensified sedimentation of hail and its accompanying melting in strong downdraft regions contribute to the increased surface precipitation at late stage of convection in polluted condition.