A numerical study of aerosol impacts on thunderstorm electrification under different water vapor conditions

Numerical simulations are carried out to investigate the impacts of varying the cloud condensation nuclei (CNN) on dynamic and microphysical processes as well as electrification and charge structure in thunderstorm clouds under different water vapor conditions by changing the relative humidity and aerosol initial concentration. The results are as follows: (1) The thunderstorm clouds will produce more small cloud droplets and precipitation process is restrained as the aerosol concentration increases. When water vapor increases, the increase in cloud drop content is faster, the content of raindrops increase, and the trend of precipitation weakening is relieved. (2) When water vapor content is relatively low, more small cloud droplets are brought into the frozen layer to form abundant ice crystal particles as the aerosol concentration increases. The content of graupel increases, and thus the electrification is enhanced. When the aerosol concentration increases to a certain level (3000 cm⁻³), the decrease in ice crystal size and raindrop content restrain the growth of graupel particles, and the electrification is restrained. Therefore, the occurrence of inductive electrification and non-inductive electrification increases first and then decreases as the aerosol concentration increases. The increase in water vapor promotes the growth of ice particles, and the electrification presents a continuous increasing trend, the charging rate reaches the maximum value at 3000 cm⁻³ aerosol concentration, and the amplification of charge density increases. (3) When water vapor content is relatively low, thunderstorm clouds are difficult to develop into a deep system and the change in aerosol concentration has little influence. The charge structure develops from tripolar to dipole in the dissipation period. When the water vapor content is relatively high, thunderstorm clouds can rapidly develop into a deep system. The charge distribution of thunderstorm shows a multi-layer complex structure as the aerosol concentration increases. Therefore, water vapor content plays an important role in the aerosol concentration impacts on the microphysics, electrification and charge structure of thunderstorm clouds.