Study On The Influence Of Surface Relative Humidity On The Microphysical And Electrical Process In Thunderstorms

In order to deepen the understanding of the correlation between different surface relative humidity and lightning activity,this study combined satellite observation data to regionalize China's land and explored the relationship between summer lightning activity and surface relative humidity in Nanjing and multiple directions in China.Combined with the data of surface temperature and aerosol optical depth(AOD),the possible causes of non-linear related phenomena between the two are further discussed.In this paper,based on the two-dimensional cumulus model with electrification and discharging processes of the coupled aerosol module,and combined with a mountain thunderstorm case,four sensitivity experiments with the different relative humidity conditions(60%,70%,80% and 90%)have been simulated.Further compare of the differences in the microphysical processes of thunderstorm clouds under different water vapor environments,discuss the role of different relative humidity levels in the dynamic,microphysical,and electrical processes of thunderstorm clouds,and focus on analyzing the impact of changes in relative humidity on the electrical processes of thunderstorm clouds.The main research conclusions are as follows:(1)The spatial distribution of regional lightning activity and relative humidity in summer in China is: the eastern humid region is a high-density area of lightning density,and the density of lightning decreases with increasing latitude,and the arid region in western China is a low-density area of lightning density.The lightning density in Nanjing area is positively correlated with the relative humidity,and the strong lightning activity in this area may be related to higher relative humidity(more than 90%).(2)In the four typical regions of China,the relationship between lightning activity and surface relative humidity is non-linear.In areas where the relative humidity is greater than 80%(or less than 55%),the lightning density is negatively correlated(positively correlated)with the relative humidity.(3)The occurrence of lightning activity requires certain humidity conditions.In dry areas on land,the increase in humidity is conducive to the occurrence of lightning activity;but in areas where the relative humidity is too high,excessive humidity may reduce convection activity The ability to rise,thereby inhibiting the occurrence of lightning activity.(4)In areas with high relative humidity on the ground,temperature conditions may be the main factors that cause increased lightning activity;in areas with median relative humidity on the ground,high-concentration aerosols may reduce the ability of convective activity through radiation effects.The key reason why thunderstorm activity is suppressed;in the middle and high values of surface relative humidity,the reason why the lightning density and the surface humidity are weak in this area may be related to the influence of monsoon or atmospheric currents;in the low value of surface relative humidity,special terrain The increase in conditions and ground humidity is conducive to creating conditions for the occurrence of lightning.(5)The relative humidity has obvious differences in the dynamics and microphysical characteristics of thunderstorm clouds.As the relative humidity increases,the number of cloud droplets increases and the ascending wind speed increases;when the relative humidity increases,the larger updraft and cloud water content help to produce larger-sized ice crystals and haze particles;the larger cloud droplets,Ji and ice crystals promote charge separation through non-inductive electrification and induction electrification mechanisms.(6)The electrification process of thunderstorm clouds is significantly affected by relative humidity.When the relative humidity increases from 60% to 90%,due to the increase in particle number concentration,the non-inductive electrification rate and the induced electrification rate increase significantly,and the total flash number increases.In addition,the greater the RH,the faster and more the charge separation Strong.And only when the relative humidity is as high as 90%,can the ground flash.In the case of 90% RH,some positive CG lightning is generated in thunderstorms with a dipolar charge structure.Overall,the greater the relative humidity,the faster and stronger the convection activity,which promotes the initial charge and discharge of thunderstorm clouds.