Effect Of Aerosol As CCN And IN 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 aerosol serving as condensation nuclei (CCN) and ice nuclei (IN) 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 by using aerosol activation equation. 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.A squall line occurred in North China on June 13th 2014 is simulated to discuss the different microphysical and electric processes of the thunderstorm under different IN concentration background. The results show that enhancing IN concentration increases the growth of ice crystals by deposition, riming, and the WBF process, promoting more conversion of ice crystals into snow, leading to more ice crystals and snow. Meanwhile, the number concentration of graupel increases, due to more ice and snow particles collecting more cloud drops. Enhancing IN concentration results in enhancement in electrification intensity, due to more ice particles participating in the rebounding collision process. In addition,the rebounding collision process between ice and graupel particals plays a main role in the electrical process,because the number concentration of ice crystals is two magnitude higher than the number concentration of snow.