A framework for modeling aerosol-cloud-lightning interactions: Validation of charge structure and aerosol effects

TL;DR

This paper introduces a new modeling framework within the Weather Research and Forecast Model to simulate aerosol-cloud-lightning interactions, successfully reproducing observed charge structures and elucidating aerosol effects on lightning and precipitation.

Contribution

It presents a novel, detailed framework for explicitly modeling aerosol effects on cloud electrification and lightning, incorporating multi-species aerosols and charge separation processes.

Findings

The model reproduces observed tripolar charge structures.

Increasing aerosols enhances lightning frequency.

Aerosols suppress rainfall while increasing lightning activity.

Abstract

This study develops a novel framework within the Weather Research and Forecast Model for modeling aerosol-cloud-lightning interactions. The framework explicitly represents aerosol-cloud interactions by prescribing aerosols with two configurations: an idealized setup, where both cloud condensation nuclei (CCN) and ice nucleating particles (IN) are assumed to have a single chemical composition and spatially uniform distributions; and a quasi-realistic configuration, with multi-species aerosols assigned spatially varying distributions, where hygroscopic components act as CCN, dust particles act as IN, and all aerosol species influence radiative transfer. Cloud microphysics is coupled with detailed charge separation and discharge processes to enable the lightning simulation. The framework is evaluated using two thunderstorms in Guangdong, China. For an isolated storm, the model successfully reproduces the observed tripolar charge structure (positive-negative-positive), demonstrating its capability in simulating cloud electrification. For a frontal storm, it captures well the observed precipitation and lightning, and shows that increasing CCN suppresses the rainfall while enhancing the lightning. Higher CCN concentrations produce more numerous but smaller cloud droplets, which suppresses the coalescence into rain droplets, allows a greater number of droplets to loft into the upper troposphere, and forms more but smaller cloud ice particles. This boosts graupel-ice collisions, intensifies non-inductive charging, strengthens the upper positive charge and the vertical electric-field gradient, ultimately increasing the lightning frequency. In contrast, no significant aerosol-induced invigoration of updrafts is observed. These results highlight the dominant role of aerosol microphysical effects over dynamical invigoration in modulating thunderstorm electrification and lightning activity.