Aerosol Effects on Electrification and Lightning Discharges in aMulticell Thunderstorm Simulated by the WRF-ELEC Model

Abstract. To investigate the effects of aerosol on lightning activity, the Weather Research and Forecasting (WRF) Model with a two-moment bulk microphysical scheme and bulk lightning model was employed to simulate a multicell thunderstorm that occurred in the metropolitan Beijing area. The results suggest that under polluted condition lightning activity is significantly enhanced during the developing and mature stages, while it is being delayed at the initial stage. Electrification and lightning discharges within the thunderstorm show distinguish characteristics by different aerosol conditions through microphysical processes. Elevated aerosol loading increases the cloud droplets numbers, the latent heat release, updraft and ice-phase particle number concentrations. More negative charges in the upper level are carried by ice particles and enhance the electrification process. A larger effective radius of graupel particles further increases non-inductive charging due to more effective collisions. The first lightning discharge was delayed at the beginning of polluted thunderstorm, coincident with the delayed occurrence of graupel and ice particles, which are responsible for charge generation through the non-inductive mechanism. In the continental case where aerosol concentrations are low, less latent heat releases in the upper parts of the cloud and as a consequence, the updraft speed is weaker leading to smaller concentrations of ice particles, lower charging rates and less lightning discharges.