The Hazards Posed by Mesoscale Lightning Megaflashes
AbstractLighting megaflashes extending over >100 km distances have been observed by the Geostationary Lightning Mappers (GLMs) on NOAA’s 16-series Geostationary Operational Environmental Satellites (GOES). The hazards posed by megaflashes are unclear, however, due to limitations in the GLM data. We address these by reprocessing GOES-16 GLM measurements from 1/1/2018 to 1/15/2020 and integrating them with Earth Networks Global Lightning Network (ENGLN) observations. 194,880 GLM megaflashes are verified as natural lightning by ENGLN. Of these, 127,479 flashes occurred following the October 2018 GLM software update that standardized GLM timing. Reprocessed GLM/ENGLN lightning maps from these post-update cases provide a comprehensive view of how individual megaflashes evolve.This megaflash dataset is used to generate statistics that describe their hazards. The average megaflash produces 5-7 CG strokes that are spread across 40-50% of the flash extent. As flash extent increases beyond 100 km, megaflashes become concentrated in key hotspot regions in North and South America while the number of CG and IC events per flash and the overall peak current increase. CGs in the larger megaflashes occur over 80% of the flash extent measured by GLM, while the majority contain regions where the megaflash is the only lightning activity in the preceding hour. These statistics demonstrate that there is no safe location below an electrified cloud that is producing megaflashes and current lightning safety guidance is not always sufficient to mitigate megaflash hazards.