Effects of Cloud Condensation Nuclei Concentration on the Electrification of Thunderstorm: A Numerical Simulation

In this paper, the Weather Research and Forecasting (WRF) model coupled with a non-inductive electrification mechanism and Morrison two-moment bulk microphysics scheme has been used to investigate the effect of cloud condensation nuclei (CCN) concentration on the development of thunderstorm electrification. Meanwhile, a bulk lightning parameterization scheme is incorporated into the WRF model. Fifteen examples with the initial CCN concentration changing from 500 cm^-3 to 4000 cm^-3 have been conducted. The results show that increasing CCN concentration decreases the number concentration of graupels but increases their mass content, leading to a greater mean size of graupels. On the contrary, with the increase in CCN concentration, the number concentration of ice crystals increases, while the mass content remains almost unchanged, resulting in a smaller mean size of ice crystals. In addition, the relative differences in falling speed between graupels and ice crystals increase mainly because of the changes in their size. This leads to an increase in the mean charge separation per rebounding collision. In summary, due to more ice crystals participating in the rebounding collision process and a larger mean charge separation per rebounding collision, increasing CCN concentration results in an enhancement in the electrification intensity, which leads to increases in the mean charge density.