Lightning Correlation with Environmental Variables Using the TRMM LIS

Societal and environmental impacts of lightning are experienced globally, from forest fires to the modification of the NOx cycle. Lightning occurs in intense cumulonimbus clouds, which are more likely to occur in environments with higher values of convective available potential energy (CAPE), humidity, and large-scale upward motion. While many studies have examined the relationship between the environment and intense convection or convective cloud properties and lightning, a comprehensive analysis of the relationship between the environmental state and lightning production remains lacking in the literature. This exercise is especially useful when considering the analysis of lightning potential in global climate models (GCMs), which usually determines lightning occurrence based on highly derived convective properties from whichever cumulus parameterization is being employed in the model.

Lightning flash counts and rates across the global tropics and subtropics are obtained using the Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS), and then compared to 3-hourly reanalysis data from MERRA2 for the period between 1997 and 2015. Environmental fields of interest include multiple formulations of CAPE since it varies based on the estimation of the lifting condensation level, column saturation fraction (representing the column-integrated atmospheric moisture), and omega at different atmospheric levels. The lightning and reanalysis data will be analyzed at three grid resolutions (0.5, 1, and 2.5°) to determine if there is scale sensitivity to the lightning-environmental relationships. Land vs ocean correlations will also be thoroughly investigated since lightning and thunderstorm properties are very different depending on the surface over which they occur. For example, preliminary results show that almost all lightning over land occurs at high column saturation fraction (between 0.8 and 0.9), while there is no obvious pattern between column saturation fraction and flash counts over ocean. The correlation of TRMM lightning data and these environmental parameters will give insight to what conditions are the best predictors of lightning events.