Effect of cloud condensation nuclei concentration on a hail event with weak warm rain process in a semi-arid region of China

Abstract

Although there are several studies on the effects of cloud condensation nuclei (CCN) concentration on convection, it requires more attention. A hail event in semi-arid China is simulated with four different CCN concentration levels, which correspond to the marine area, mid-continental, continental, and polluted background CCN concentrations. It was found that the auto-conversion of cloud water to rainwater is not significant in the simulated convection. The increase in CCN concentration was accompanied by a large number of graupel particles of smaller size, which consequently induced smaller rain droplets. It is shown that increasing CCN concentration changed the dominant average mass-weighted diameters of the graupel, hail particles and rain droplet. The number concentration of rain droplets increased with CCN concentration, corresponding to the significant evaporation during the falling process. Consequently, the maximum of rainfall on the ground did not increase. Additionally, increasing the CCN concentration does not have the same apparent impact on the size of hail particles.