Analysis of Geostationary Lightning Mapper Events Using VHF Broadband Interferometers

Very high frequency (VHF) broadband interferometers map the progression of lightning in 2-dimensional sky coordinates with very high time resolution. Consequently, they are able to unambiguously identify the types and characteristics of most discharge processes within a lightning flash. When this information is combined with 3-dimensional VHF source locations obtained by a lightning mapping array (LMA), a more complete picture can be obtained of discharge context within a thunderstorm.

The Geostationary Lightning Mappers (GLMs) onboard the GOES-16 and GOES-17 satellites are providing near real-time coverage of optical lightning events within the western hemisphere. While VHF radiation is unimpeded by clouds, optical radiation is heavily scattered by them. Consequently, both the depth and geometry of clouds are important considerations for GLM optical detections.

In 2018, the New Mexico Tech VHF broadband interferometer was deployed in Oklahoma during the spring and early summer seasons. This system was redeployed in Utah during the summer and will likely remain there well into the fall season. Another VHF broadband system was deployed in New Mexico for the southwest summer monsoon season. All of these locations were within lightning mapping arrays which provided supporting 3D data.

These deployments covered a wide range of thunderstorm types ranging from large supercells and mesoscale convective systems down to more ordinary isolated thunderstorms. The optical depth of discharges within these storm types varies widely along with the frequency and types of discharge processes. Consistent with previous studies [Thomas et al., Geophys. Res. Lett., 27, 2000], there is a strong bias towards detection of events near cloud top. In particular, fast K-change events are rarely detected by a GLM unless they propagate into the upper levels of a storm. The same is true of negative leaders, which comprise the majority of GLM detections. The detection efficiency for these and other discharge processes will be explored in this presentation for the various locations and thunderstorm types.