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In this study, we analyze 44 terrestrial gamma-ray flashes (TGFs) detected by the Fermi Gamma-ray Burst Monitor (GBM) occurring in 2014–2016 in conjunction with data from the U.S. National Lightning Detection Network (NLDN). We examine the characteristics of magnetic field waveforms measured by NLDN sensors for 61 pulses that occurred within 5 ms of the start-time of the TGF photon flux. For 21 (out of 44) TGFs, the associated NLDN pulse occurred almost simultaneously with (that is, within 200 μs of) the TGF. One TGF had two NLDN pulses within 200 μs. The median absolute time interval between the beginning of these near-simultaneous pulses and the TGF flux start-time is 50 μs. We speculate that these RF pulses are signatures of either TGF-associated relativistic electron avalanches or currents traveling in conducting paths “preconditioned” by TGF-associated electron beams. Compared to pulses that were not simultaneous with TGFs (but within 5 ms of one), simultaneous pulses had higher median absolute peak current (26 kA versus 11 kA), longer median threshold-to-peak rise time (14 μs versus 2.8 μs), and longer median peak-to-zero time (15 μs versus 5.5 μs). A majority (77%) of our simultaneous RF pulses had NLDN-estimated peak currents less than 50 kA indicating that TGF emissions can be associated with moderate-peak-amplitude processes. The lightning flash associated with one of the TGFs in our data set was observed by a Lightning Mapping Array, which reported a relatively high-power source at an altitude of 25 km occurring 101 μs after the GBM-reported TGF discovery-bin start-time.
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Compton Scattering Effects on the Spectral and Temporal Properties of Terrestrial Gamma‐Ray Flashes
Abstract Terrestrial gamma‐ray flashes (TGFs) are high‐energy photon bursts originating from the Earth's atmosphere. In this study, using first‐principles Monte Carlo simulations, we quantify the effects of Compton scattering on the temporal and spectral properties of TGFs induced by a tilted source geometry. Modeling results indicate that the source orientation is a critical parameter in TGF analysis but has been significantly underestimated in previous studies. Offset distance between the lightning source and satellite location cannot be used as a single parameter characterizing Compton scattering effects. In the tilted geometry, Compton scattering effects are more pronounced in the falling part of TGF pulses and can lead to an increase of the falling part of TGF pulses by several tens of microseconds. Moreover, by performing curve‐fitting analysis on simulated TGF light curves, we explain how the symmetric and asymmetric pulses measured by the Gamma‐Ray Burst Monitor on Fermi satellite are consistent with the Compton scattering effects. Fermi‐measured TGF pulses can be fully explained using Gaussian‐distributed TGF sources with an average duration of ∼206 μs.
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- Award ID(s):
- 1744099
- PAR ID:
- 10448821
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 124
- Issue:
- 8
- ISSN:
- 2169-9380
- Page Range / eLocation ID:
- p. 7220-7230
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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