Characterizing lightning emissions that cause gamma ray flashes



[1] Terrestrial gamma ray flashes (TGFs) are bursts of high-energy radiation released in Earth's atmosphere during thunderstorms and are believed to be associated with lightning. Progress has been made in their study, but much remains to be learned about the properties of these events and related lightning activity. To characterize the lightning processes that produce TGFs, Lu et al. analyzed 56 TGFs detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite from 2004 to 2009. They looked at the timing and characteristics of the very low frequency (VLF) and ultralow-frequency (ULF) emissions that occur in conjunction with TGFs. The researchers determined that the large majority of TGF-associated lightning signals contain at least one VLF impulse superimposed on a slow ULF pulse, indicative of significant upward negative charge transfer within 2–6 milliseconds; gamma rays are emitted in the course of this slow process, suggesting that this process plays a key role in gamma ray production, the authors report. (Journal of Geophysical Research-Space Physics, doi:10.1029/2010JA016141, 2011)