Photoelectric Effect in Air Explains Lightning Initiation and Terrestrial Gamma Ray Flashes

Terrestrial gamma ray flashes (TGFs) are high-energy photon bursts that have been linked to short bursts of electromagnetic radiation associated with lightning activity. The most puzzling unexplained aspect of these events is that gamma rays originate from very compact regions of space while the source regions often seem to be optically dim and radio silent when compared to processes in ordinary lightning discharges. In this work, we report a mechanism that allows precise quantitative explanation of these peculiar features of TGFs and their relationships to the observed waveform characteristics of associated radio emissions. The mechanism represents an extension of earlier ideas on feedback processes in growth of relativistic runaway electron avalanches (Dwyer, 2003, https://doi.org/10.1029/2003GL017781), and is based on a recent demonstration of the dominant role of the photoelectric feedback on compact spatial scales (Pasko, Celestin, et al., 2023, https://doi.org/10.1029/2022GL102710). Since discussed events often occur in isolation or precede formation of lightning discharges, the reported findings propose a straightforward solution for the long-standing problem of lightning initiation.