Effects of Different Aerosols on Cloud-to-ground Lightning Activity in the Yangtze River Delta

Abstract

Lightning activity poses threats to human life and property safety. A large volume studies indicate that aerosol plays a significant role in lightning activity. To explore the effect of different types of aerosols on lightning activity in the Yangtze River Delta and its surrounding areas, cloud-to-ground (CG) lightning location data and aerosol optical depth from reanalysis dataset is analyzed in the target area(27.5°-35°N, 115°-122.5°E) during 2015-2021.The spatial distribution of aerosol optical depth (AOD) with CG lightning condition and without CG lightning condition, and monthly variation of aerosol concentration under two conditions are investigated. All the grids in the target region show that sulfate AOD is higher, while dust AOD is lower with CG lightning. In summer there are little differences between the AOD with CG lightning and without CG lightning conditions. In other months, more sulfate aerosol and less dust aerosol are found with CG lightning condition.The spatial distribution of CG lightning density difference under higher and lower AOD conditions is given. The results show that when the sulfate AOD is high, the CG lightning density of most grids is higher. The CG lightning density is significantly lower when the dust AOD is high.The correlation coefficient between CG lightning density and the AOD for different types of aerosols is calculated for the months when CG lightning is active. When the concentration of sulfate aerosol is low, the correlation coefficient between sulfate AOD and CG lightning density is significant. When the sulfate aerosol concentration exceeds a certain threshold, there is no significant correlation between CG lightning density and sulfate AOD. The positive correlation may be due to the fact that the cloud microphysical effect of sulfate aerosols can promote the development of convection. With sufficient water vapors, sulfate aerosols form cloud condensation nuclei and promote CG lightning activity. When the concentration of sulfate aerosols is higher than the threshold value, the cloud microphysical effect and the radiation effect of aerosol may be counterbalanced, which may lead to weak correlation between CG lightning density and aerosol concentration. The results also show a weak negative correlation between dust aerosol and CG lightning density in April, May, June, and no significant correlation in July, August, September. Considering the low concentration of dust aerosols in the Yangtze River Delta and its surrounding areas, the inhibitory effect of dust aerosols on CG lightning activity may not be just explained by the radiation effect. The large particle size of dust aerosol may play a significant role in suppressing CG lightning activity.

Keywords

• cloud-to-ground lightning activity
• aerosol
• cloud microphysics