Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration,Nanjing University of Information Science Technology
The Weather Research and Forecasting model with a spectral-bin microphysical scheme (WRF-SBM) was used to simulate a hailstorm occurred in summer of Xinjiang. The effects of aerosol concentration on microphysical characteristics and precipitation of the hailstorm as well as formation mechanism of hail are studied by sensitivity tests. The results show that the convection of the hailstorm is stronger with larger aerosol concentration. At the development stage of the hailstorm, the liquid water content increases with the increase of aerosol concentration and the ice water content is the highest under moderate polluted condition. The hail mixing ratio increases first and then decreases with the increase of aerosol concentration. Under moderate polluted condition, there is appropriate cloud droplet size and relatively sufficient supercooled water, which is favor for the transformation of water from liquid phase to ice phase and therefore contributing to hail growth. Hail is initially formed by the riming of supercooled liquid water by ice crystals, but this process is rapidly weakened after the development of hailstorm. Then the freezing of droplets becomes the main source of hail for a short while. However, once the hail is formed, it will grow rapidly by collecting the supercooled water, which becomes the dominant process of the hail growth. The severe polluted condition will postpone the onset of hail formation processes. With enhanced aerosol loading, the surface accumulated liquid precipitation is increased while the ice phase precipitation is increased first and then reduced. The moderate aerosol concentration leads to larger amount of hail mixing ratio and higher percentage of hail in ice-phase precipitation. However, with further increased aerosol concentration, both values are reduced. Therefore, we propose “the optimal aerosol concentration” that is most suitable for hail growth.