1/22/2024 0 Comments Radio gamma internationalTGFs reported from ground-based observations are associated with (usually high-intensity) cloud-to-ground discharges effectively transporting negative charge to ground. TGFs are typically detected worldwide by satellite-based instruments 1, 8, but several ground-based 9, 10, 11, 12, 13, 14 and two aircraft-based 15, 16 observations have been made. However, some important parameters of the processes leading to the production of TGFs, such as the spatial-scale of the electron-acceleration region and the source of the seed particles necessary for the RREA processes, as well as the current and charge-transfer characteristics of TGFs remain unknown. A leading hypothesis for TGF-production is the Relativistic Runaway Electron Avalanche (RREA) 6, 7 process followed by bremsstrahlung photon emission occurring in the presence of thundercloud electric fields. Some models assume that charged particles are accelerated in the relatively-high electric field region concentrated at the tips of lightning leaders 2, 3, while other models consider the particle-acceleration to occur in large-scale electric fields in thunderclouds 4, 5. The mechanism for creating the causative high-energy electrons in the source region still remains unclear. TGFs are one of the highest-energy (10–20 MeV or more) natural photon emissions on Earth. 1, are brief (typically less than 1 ms) bursts of energetic gamma-ray photons generated during thunderstorms. Terrestrial gamma ray flashes or TGFs, a phenomenon discovered relatively recently by Fishman et al. This provides independent evidence that the EMPs and TGFs are produced by the same phenomenon, rather than the EMPs being from “regular” lightning in TGF-producing thunderstorms. TGFs detected by the GBM with sources at farther horizontal distances are expected to be intrinsically brighter and were found to be associated with EMPs having larger median peak-amplitudes. We examined, for the first time, the dependence of the TGF-associated EMP-peak-amplitude on the horizontal offset distance between the Fermi spacecraft and the TGF source. ![]() Here we show the existence of two categories of TGFs − those that were accompanied by quasi-simultaneous electromagnetic pulses (EMPs) detected by the GLD360 and those without such simultaneous EMPs. Radio frequency (RF) measurements were obtained from the Global Lightning Dataset (GLD360). The Gamma-ray Burst Monitor (GBM) on board the Fermi spacecraft provided the energetic radiation measurements. In this study, we analyze an unprecedentedly large dataset comprised of 2188 TGFs whose signatures were simultaneously measured using space- and ground-based detectors over a five-year period. ![]() Terrestrial gamma ray flashes (TGFs) are a class of enigmatic electrical discharges in the Earth’s atmosphere.
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