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arXiv · 1810.03853

Characterizing upward lightning with and without a terrestrial gamma-ray flash

D. M. Smith·G. S. Bowers·M. Kamogawa·D. Wang·T. Ushio·J. Ortberg·J. R. Dwyer·M. Stock
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Abstract

We compare two observations of gamma-rays before, during, and after lightning flashes initiated by upward leaders from a tower during low-altitude winter thunderstorms on the western coast of Honshu, Japan. While the two leaders appear similar, one produced a terrestrial gamma-ray flash (TGF) so bright that it paralyzed the gamma-ray detectors while it was occurring, and could be observed only via the weaker flux of neutrons created in its wake, while the other produced no detectable TGF gamma-rays at all. The ratio between the indirectly derived gamma-ray fluence for the TGF and the 95% confidence gamma-ray upper limit for the gamma-ray quiet flash is a factor of $1\times10^7$. With the only two observations of this type providing such dramatically different results -- a TGF probably as bright as those seen from space and a powerful upper limit -- we recognize that weak, sub-luminous TGFs in this situation are probably not common, and we quantify this conclusion. While the gamma-ray quiet flash appeared to have a faster leader and more powerful initial continuous current pulse than the flash that produced a TGF, the TGF-producing flash occurred during a weak gamma-ray "glow", while the gamma-ray quiet flash did not, implying a higher electric field aloft when the TGF was produced. We suggest that the field in the high-field region approached by a leader may be more important for whether a TGF is produced than the characteristics of the leader itself.

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D. M. Smith, G. S. Bowers, M. Kamogawa, D. Wang, T. Ushio, J. Ortberg, J. R. Dwyer, M. Stock. 2018-10-09. Characterizing upward lightning with and without a terrestrial gamma-ray flash. https://doi.org/10.1029/2018jd029105

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