We previously documented geographic distributions of the optically brightest lightning on Earth – known as “superbolts” – using two space-based instruments: the photodiode detector (PDD) on the Fast On-orbit Recording of Transient Events (FORTE) satellite and the Geostationary Lightning Mapper (GLM) on NOAA’s newest Geostationary Operational Environmental Satellites (GOES). In this study, we further examine the superbolts identified by the PDD and GLM to reconcile the differences between their geographic distributions. We find that both the physical extent of the parent flash and the development speed of its leaders are important for making a superbolt.

The oceanic PDD superbolts tend to occur early in flashes that rapidly expand laterally into long-horizontal “megaflashes.” The top GLM superbolts occur over land at later times in particularly large megaflashes that grow more slowly until they extend over multiple hundreds of kilometers. The FORTE PDD missed these delayed superbolts due to limitations in its triggering.

Coincident TRMM measurements show that the warm season megaflash superbolts detected by LIS/GLM and Turman’s (1977) wintertime oceanic superbolts also observed by the PDD occur in otherwise similar thunderstorm environments. Both are marked by: low storm heights (< 10 km), widespread rainfall near the surface, small infrared brightness temperature gradients, and low flash rates. We suggest that the vertically-compact, stratiform nature of these clouds allows them to store more charge between flashes, providing favorable conditions for superbolt production.