Characterizing the TGF-Lightning Relationship Using ENTLN

Comparing the timestamps of TGFs (terrestrial gamma flashes) detected by the GBM instrument on the Fermi space telescope to those of ENTLN (Earth Networks Total Lightning Network) radio lightning detections allows association of TGFs with individual lightning strokes. The ENTLN network is used due to its high detection efficiency for IC (intra-cloud) lightning. Examining all TGFs with strong ENTLN radio associations reveals three distinct timescales of activity. The shortest timescale component includes radio signals within ±200 μs of the TGF. The second component includes radio signals within ±6 ms of the TGF. The third component occurs after the TGFs out to ~800 ms. Signals in the first component are predominantly the TGFs themselves. The pattern of signals in the second and third components confirms the hypothesis in which IC lightning travels from the upper negative charge layer to the upper positive charge layer, generating a TGF, followed by a flurry of further lightning activity that propagates through both layers. Specifically, the second timescale component consists of vertical strokes, during which TGFs can occur randomly. The third component is the horizontal activity that follows.