An Investigation of Geostationary Lightning Mapper Flash Extent

Abstract:

Flashes can extend for tens or hundreds of kilometers and each has the potential to come to ground multiple times. There is limited literature documenting the spatial extent, distribution of flash size, and where the largest flashes are most common. This is, in part, due to limitations in lightning observation systems. These include observing spatial extent but limited range (i.e, lightning mapping arrays) or having greater coverage but lacking spatial extent or a low Earth orbit (i.e., NASA’s low Earth orbiting Optical Transient Detector and Lightning Imaging Sensors). The advent of Geostationary Lightning Mapper (GLM) observations providing continuous, near hemispheric observations gives a new opportunity to observe and analyze the spatial extent of flashes. Prior to the GLM, the longest flash confirmed by the World Meteorological Organization was observed in Oklahoma (321 km). The GLM has recently been confirmed to have observed a new record flash of 709 km.

The GLM Lightning Cluster Filter Algorithm (LCFA) is configured specifically for near real-time processing. In order to maintain latency requirements, flashes that exceed thresholds of groups (101) or duration (3 s) are terminated and categorized as “degraded”. The Global Hydrology Resource Center Distributed Active Archive Center (GHRC DAAC), a joint venture between the University of Alabama in Huntsville (UAH) and NASA, is collaborating with Los Alamos National Laboratory (LANL) to use the GLM-Cluster Integrity, Exception Resolution, and Reclustering Algorithm (GLM-CIERRA). The algorithm does not reprocess the GLM LCFA output, but reassembles flashes split by the LCFA.

Using GLM-CIERRA, this presentation will conduct a first of its kind evaluation of lightning spatial extent from GLM observations from 2018-2019. This includes over 700 million flashes. The early analysis indicates that the top 1% of all flashes are > 45.8 km. For reference, this 1% of flashes (i.e., ~7 million) is equivalent to half the number of all flashes recorded by LIS in 17 years. Other results show that in two years there are almost 270,000 flashes > 100 km and nearly 1,800 exceeding 300 km. Early work by co-author Peterson has further shown that flashes exceeding 321 km and 7.78 s are primarily concentrated in the eastern two-thirds of the United States and southeastern South America.