Processes in -CG lightning flashes detected from space by GLM: A ground-truth study in the Amazon

Negative lightning flashes involve a number of different processes, including preliminary breakdown, stepped leaders, return strokes, continuing currents, and M-components. The Geostationary Lightning Mapper (GLM) onboard of Geostationary Operational Environmental Satellite R-series (GOES-R) is an optical lightning detector. The GLM provides three types of data: events, groups, and flashes. According to GLM designers, the group data are intended to track strokes. We recorded wideband lightning electric fields in the Amazon and compared them with the corresponding GLM group data (optical energy) to investigate what lightning processes can be detected by GLM from space. Based on a sample of 13 -CG flashes containing 37 return strokes, we found that GLM detected all the return strokes. It also detected what appeared to be IC branches, but did not detect one CID/NBE that occurred after a RS in a -CG flash. Further, the GLM detected 70% of first-stroke leaders (9 out of 13), as well as subsequent-stroke leaders in five multiple-stroke flashes. The GLM did not detect any preliminary breakdown processes. Two return strokes were followed by luminosity detections lasting for more than 10 ms, indicating some continuing current flowing in the lightning channel to the ground.