Validation of GLM Flash Rates in Isolated Deep Convection

Abstract:

The Geostationary Lightning Mapper (GLM) aboard GOES-16 and GOES-17 have documented millions of lightning flashes since the satellites entered orbit. One main goal of GLM was to lengthen lead times for severe thunderstorm warnings by capturing sharp changes in lightning flash rate termed “lightning jumps”. In this thrust, it is important to understand the detection efficiency of GLM. The validation of GLM flash rates can be ascertained in part by comparing lightning flash rates from GLM to those measured by VHF Lightning Mapping Array networks. A simple ratio of GLM flashes to LMA flashes termed the “GLM Detection efficiency” can therefore be determined for isolated thunderstorms. This study includes analysis of isolated deep convection in Alabama, Colorado, and West Texas. A total of 34 convective storms were included in this study. The results suggest that the GLM flash rate is less than that measured by LMA in many storms. We find that when the LMA flash rate is greater than 50 flashes min^-1, the GLM detection efficiency is generally below 25%. While part of the low detection efficiency can be attributed to increasing GLM detection thresholds at the edges of the instrument’s field of view, we demonstrate by these many case studies that flash size and optical attenuation by cloud particles contribute significantly to DE reduction.