A Numerical Study of Aerosol Effects on Microphysical Process and Electrification in Thunderstorms

A two-dimensional (2-D) cumulus model with electrification and lightning processes is implemented to investigate aerosol effects on microphysical process, electrification, and charge structure in thunderstorms. The 2-D cumulus model coupled with a droplet freezing module is used to simulate a SEET (Studies of Electrical Evolution in Thunderstorms) case. The results show that the number concentration of cloud droplets increases and its scale decreases with increasing aerosol concentration, but the content of raindrops reduces. Ice crystals grow rapidly in low temperature region, which is attributed to droplets freezing, and the number concentration of ice crystals increases but the scale decreases. The number concentration of graupels increases first and then decreases sharply because ice crystals are difficult to grow into graupels with larger scale when the aerosol concentration exceeds 1000 cm^-3. In addition, the charge structure of thunderstorms is not affected by aerosol concentration, but aerosols have significant effect on the strength of electrification, i.e., when the aerosol concentration is lower, more ice crystals and graupels collision enhances the non-inductive charging process and increases the charge density as the aerosol concentration increases; however, the non-inductive charging rate starts to decrease when the aerosol concentration exceeds 1000 cm^-3 due to the appearance of small ice crystals and little graupels, and the charge density is reduced.