Understanding the Effects of Aerosols on Electrification and Lightning Polarity in an Idealized Supercell Thunderstorm via Model Emulation

Abstract

Abstract Aerosol effects on the lightning intensity and polarity of a continental supercell storm were investigated using a three-dimensional lightning scheme within the Weather Research and Forecasting model. We find that both intra-cloud (IC) and cloud-to-ground (CG) flashes are enhanced by the increasing number of cloud condensation nuclei (CCN), especially the percentage of positive CG (+CG) strokes peaking at 42%. Electrical characteristics of the storm varied in different aerosol scenarios through microphysical processes. Added aerosols increase the number of cloud droplets and ice-phase hydrometeors. The greater ice-crystal concentration and larger graupel size ensure sufficient charge separation, leading to higher charge density and more lightning discharges. In addition, an inverted polarity charge structure with a strong positive?charge region in the mid?levels was formed mainly due to the positively charged graupel in the presence of higher supercooled cloud water content. Positive lightning channels originating from this positive-charge region propagated to the ground, producing more +CG strokes. When the aerosol concentration was low, the charge density in the upper positive-charge region was much lower due to smaller ice-particle content. Consequently, there were barely any +CG strokes. Most of the negative CG flashes deposited positive charge in the lower negative-charge region.