Ground- and Space-Based Observations of Horizontally Extensive Lightning Flashes

Horizontally-extensive lightning flashes occur frequently in association with mature and late phases of multicellular thunderstorms, both in trailing stratiform regions and horizontally-extensive anvils. The spatial relationship between these flashes and the parent cloud volume is of importance for space launch operational decision making, and more importantly, general lightning safety. These horizontally-extensive flashes can produce cloud-to-ground strokes far away from the convective core and where there is heavy rain. Before this topic can be accurately studied, there is a need to understand the degree to which current lightning observation systems can depict the spatial extent of these long flashes.

In this ongoing work, we will inter-compare the depiction of these horizontally-extensive flashes using several ground-based lightning locating systems (LLSs) located at Kennedy Space Center (KSC) with space-based observations observed by the recently-launched Geostationary Lightning Mapper (GLM) onboard the GOES-16 satellite. The ground-based datasets include the KSC Lightning Mapping Array (KSCLMA), the operational narrow-band digital interferometer network known as MERLIN, and the combined cloud-to-ground and cloud lightning dataset produced by the U.S. National Lightning Detection Network (NLDN). The KSCLMA system is a network of VHF time-of-arrival sensors that preferentially report and locate breakdown processes, and MERLIN is a geolocation network of VHF interferometers that each “point” to the discharges in the horizontal plane. MERLIN preferentially reports emissions lasting 100 microseconds or longer, generally produced by leaders propagating in established (ionized) channels.

Observations to date indicate that MERLIN and the KSCSLMA provide similar overall descriptions of the spatial and temporal extent of these flashes. The KSC LMA system has good location accuracy, and provides excellent 3-dimensional representation within ~100 km of KSC. It also has sufficient sensitivity to provide 2-dimensional flash mapping within ~250 km of KSC. The MERLIN system provides a more-detailed representation of fast leader propagation (in 2 dimensions) with ~100 km of KSC. Earlier work during the CHUVA campaign in Brazil with similar systems and the satellite-based sensor Lightning Imaging System (LIS) has shown that the interferometric data correlated much better in space and time with the LIS optical observations. This work discusses this relationship at KSC, where both the LMA and digital interferometer network perform much better than the systems used during CHUVA.