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

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.

A 3D Numerical Model to Estimate Lightning Types for PyroCb Thundercloud

“…There is no significant observational evidence indicating that high aerosol concentrations increase cloud electrification in pyroCb storms. According to the sensitivity analysis presented in previous studies [34,36,39], there is a noticeable non-linear relationship between the values of positive and negative charge densities and aerosol concentrations which can significantly affect the cloud charge structure. However, this paper does not aim to determine any qualitative link between aerosol concentrations and electrification.…”

“…This process lowers the efficiency of droplet collisions, which delays and inhibits the formation of raindrops. Studies in [34][35][36][37][38][39] have identified a positive correlation between lightning activity and aerosol concentrations. Additionally, those works demonstrate that high aerosol concentrations can significantly enhance the electrification process, according to the bulk microphysical model, or even weaken the electrification on further increase.…”

Lightning response to temperature and aerosols

“…Different nucleation schemes in simulations affect the participation of aerosols in the electrification process. Sun et al (2024) studied the effects of aerosols on the electrification and lightning based on the WRF-ELEC model (Fierro et al 2013) coupled with a sophisticated explicit charging parameterization (Saunders and Peck 1998) and three-dimensional lightning scheme (MacGorman et al 2001, Mansell et al 2005. They suggested that both IC, CG flashes and fraction of +CG are all increased by adding CCN concentrations through modifying the microphysical processes.…”

A CloudSat and CALIPSO‐Based Evaluation of the Effects of Thermodynamic Instability and Aerosol Loading on Amazon Basin Deep Convection and Lightning

“…Observations and numerical simulations suggest that adding aerosols to a pristine environment intensifies deep convection through aerosol-induced changes in the mixed phase layer of the cloud that enhance lightning (Fan et al, 2018;Sun et al, 2023Sun et al, , 2024. As the aerosol amount continues to increase, a larger population of tiny droplets begins to suppress the growth of graupel and the delivery of large, supercooled droplets to the mixed phase region thus suppressing charge separation and flash rates (Williams et al, 2002).…”