Different aerosol effects on the daytime and nocturnal cloud-to-ground lightning in the Sichuan Basin

Abstract. The effect of aerosols on lightning has been involved in many studies, but its mechanisms are complex and far from understood. The relationship between cloud-to-ground (CG) lightning and aerosols on an hourly time scale in the Sichuan Basin during 2010–2018 was investigated. The effects of aerosols, dynamics-thermodynamics factors (convective available potential energy: CAPE and vertical wind shear: SHEAR) and cloud-related factors (total column cloud liquid water: TCLW and total column cloud ice water: TCIW) on the CG lightning flashes on day and night were analysed. The diurnal variation of CG lightning flashes has two peaks under clean conditions, while only one peak was found in the diurnal variation of ground flash under polluted conditions. In the early morning and night, more CG lightning flashes were found under polluted conditions, but in other periods, the difference in the CG lightning flashes between polluted and clean conditions is insignificant. Similar results were also found in the percentage of positive CG lightning flashes. At night, aerosols are positively correlated with the CG lightning flashes, and the response of CG lightning flashes to CAPE, SHEAR and TCLW is more evident under high aerosol loading. In the afternoon, aerosols have no significant effects on CG lightning and its response to dynamics-thermodynamics and cloud-related factors. This difference seems to be caused by the different impacts of aerosol radiative and microphysical effects in these two periods. In the afternoon, aerosols may directly (indirectly) reduce the solar radiation reaching the ground and suppress convection through aerosol radiative effects (aerosol microphysical effects). Aerosols may also stimulate convection through microphysical effects. In this period, the two opposite effects of aerosols on convection offset each other. At night, without solar radiation, the aerosol microphysical effects may play a dominant role in the entire AOD range to promote convection.