Evidence for Extended Charging Periods Prior to Terrestrial Gamma‐Ray Flashes

We present an analysis of lightning interflash intervals in 219 terrestrial gamma ray flash (TGF) producing thunderstorms. Clustering was used to identify groups of lightning sferics, interpreted as individual thunderstorms, in combined World Wide Lightning Location Network and Earth Networks Total Lightning Network data. In these individual groups of sferics, analysis was done on the lightning flash frequency within +/- 10 min of the Fermi recorded TGF. We find that typical interflash intervals immediately prior to TGFs are 24% longer than mean interflash intervals in their individual producing storms, while the interflash intervals immediately following the TGFs are typically 8% shorter than normal. The significance of these results, tested using a numerical bootstrap method, was found to be highly significant for the pre-TGF interval. These results could imply that a stronger electric field is necessary for the production of TGFs and may help to explain why some lightning strikes produce TGFs while others do not.