Diurnal differences in the effect of aerosols on cloud-to-ground lightning in the Sichuan Basin

Abstract

The effect of aerosols on lightning has been examined in many studies, but its mechanisms are complex and far from understood. This study investigated the influence of aerosols on cloud-to-ground (CG) lightning during both afternoon (12:00–18:00 Beijing Time) and night (23:00–05:00 Beijing Time) in the Sichuan Basin by analysing 9-year datasets of CG lightning, aerosol loading, dynamic-thermodynamic, and cloud-related data from ground-based measurements, satellite, and model reanalysis to understand the difference in the influences of aerosols under conditions with and without solar radiation. The relationship between lightning and aerosol optical depth (AOD) is nonlinear in the afternoon and at night with a turning point at AOD ≅ 0.3. When AOD is less than 0.3, increasing AOD will lead to an increase in lightning flashes both in the afternoon and at night. When the AOD exceeds 0.3, the increase of AOD will reduce the lightning flashes in the afternoon but have no obvious effect on the lightning flashes at night. The different relationship between aerosol loading and lightning flashes in the afternoon and at night after AOD exceeds 0.3 is related to the changes in solar radiation in these two periods. In the afternoon, excessive aerosols reduce the solar radiation reaching the ground through its direct and indirect radiative effects, resulting in the decrease of the surface temperature, increasing atmospheric stability, inhibiting convection, and thus reducing lightning. At night, due to the absence of solar radiation, the influence of aerosols on surface temperature is weakened; thus, the inhibition of aerosols on lightning activity is weakened.