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  • Determining a Lower Limit of Luminosity for the First Satellite Observation of a Reverse Beam Terrestrial Gamma Ray Flash Associated With a Cloud to Ground Lightning Leader
Title: Determining a Lower Limit of Luminosity for the First Satellite Observation of a Reverse Beam Terrestrial Gamma Ray Flash Associated With a Cloud to Ground Lightning Leader
Abstract We provide an updated analysis of the gamma ray signature of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma ray Burst Monitor first reported by Pu et al. (2020,https://doi.org/10.1029/2020GL089427). A TGF produced 3 ms prior to a negative cloud‐to‐ground return stroke was close to simultaneous with an isolated low‐frequency radio pulse during the leader’s propagation, with a polarity indicating downward moving negative charge. In previous observations, this “slow” low‐frequency signal has been strongly correlated with upward‐directed (opposite polarity) TGF events (Pu et al., 2019,https://doi.org/10.1029/2019GL082743; Cummer et al., 2011,https://doi.org/10.1029/2011GL048099), leading the authors to conclude that the Fermi gamma ray observation is actually the result of a reverse positron beam generating upward‐directed gamma rays. We investigate the feasibility of this scenario and determine a lower limit on the luminosity of the downward TGF from the perspective of gamma ray timing uncertainties, TGF Monte Carlo simulations, and meteorological analysis of a model storm cell and its possible charge structure altitudes. We determined that the most likely source altitude of the TGF reverse beam was 7.5 km ± 2.6 km, just below an estimated negative charge center at 8 km. At that altitude, the Monte Carlo simulations indicate a lower luminosity limit of 2 × 1018photons above 1 MeV for the main downward beam of the TGF, making the reverse beam detectable by the Fermi Gamma ray Burst Monitor.  more » « less
Award ID(s):
2235299 2026304
PAR ID:
10462863
Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Atmospheres
Volume:
128
Issue:
18
ISSN:
2169-897X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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