A closer examination of terrestrial gamma‐ray flash‐related lightning processes

Abstract

This paper presents detailed comparisons between terrestrial gamma‐ray flashes (TGFs) detected by the RHESSI satellite and the lightning processes observed by the Los Alamos Sferic Array (LASA). It was found that all RHESSI‐detected TGFs were related to normal intracloud flashes that transported electrons upward in the cloud. Detailed temporal comparisons suggest that TGFs are more likely related to small, rather than large, lightning pulses, mostly at the level of 10−1−100 V/m when the pulses are normalized to an observation distance of 100 km. The corresponding peak current was estimated to be 3–19 kA with most of them below 10 kA, if the discharges were assumed to be individual steps in a stepped‐leader process. If the discharges were considered to be directly associated with runaway breakdown processes with a current propagation speed of c, the peak current would be 0.4–3.2 kA. Analysis of events that were close to the LASA stations showed that TGFs were most likely to occur during the initial milliseconds of IC flashes while the discharge developed vertically upward from the negative to the positive charge regions in the cloud. The heights of the TGF‐related lightning pulses were estimated to be in the range of 10.5–14.1 km along the upward development. An intense NBE with a peak current of 80 kA and a height of 16.1 km was found 2.9 ms after one TGF, and is believed to not be directly associated with the TGF but may be preconditioned by the TGF‐related discharge process.