Photonuclear Reactions in Lightning: 2. Comparison Between Observation and Simulation Model. Issue 20 (9th October 2020)

• Record Type: Journal Article
• Authors: Wada, Y.; Enoto, T.; Nakazawa, K.; Yuasa, T.; Furuta, Y.; Odaka, H.; Makishima, K.; Tsuchiya, H.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 20(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-09
• Subjects: photonuclear reaction -- lightning -- thunderstorm -- high‐energy atmospheric physics -- terrestrial gamma‐ray flash; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD033194
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: During a winter thunderstorm on 6 February 2017 in Japan, photonuclear reactions such as 14 N( γ, n ) 13 N were triggered by a downward terrestrial gamma‐ray flash (TGF), as reported by Enoto et al. (2017, https://doi.org/10.1038/nature24630 ). In the present paper, we compare the observation with a simulation model of downward TGFs and subsequent photonuclear reactions constructed by the first paper of the series and Wada, Enoto, Nakazawa, et al. (2019, https://doi.org/10.1103/physrevlett.123.061103 ). The observation and model consist of three components: annihilation gamma rays from positrons produced by β + ‐decay nuclei, deexcitation gamma rays originating from neutron captures, and radiation doses by TGF photons. Each component of the observation is reproduced by the simulation model, and we constrain a relation between the number of avalanche electrons and their production altitude of the downward TGF. The constraints by three components match within an order of magnitude. The downward TGF is estimated to comprise (0.5–2.5) × 10 19 avalanche electrons above 1 MeV produced at an altitude of 1.4–2.7 km. Despite differences in altitude, direction, and season, downward TGFs in winter thunderstorms are thought to have the same mechanism of electron acceleration and multiplication in lightning as TGFs observed by in‐orbit satellites. Plain Language Summary: Lightning flashes are sometimes accompanied by strong high‐energy emission called "terrestrial gamma‐ray flashes" (TGFs). The energy of gamma rays in TGFs is high enough to trigger nuclear reactions with atmospheric nuclei such as nitrogen and oxygen. The nuclear reactions produce neutrons and unstable isotopes that emit positrons. In the companion paper of this series, we calculated the nuclear reactions and propagation processes of their products such as positrons and neutrons and modeled their characteristics at ground level by simulations. In the present paper, the simulation model is compared with the actual observation of a TGF and nuclear reactions during winter thunderstorms in Japan. The model successfully reproduces the observation and estimate the production altitude the number of energetic electrons involved in the TGF. Key Points: A simulation model of photonuclear reactions in lightning is compared with an observation during a winter thunderstorm reported by Enoto et al. (2017, https://doi.org/10.1038/nature24630 ) Three detected signatures originating from positrons, neutrons, and TGF photons are reproduced by the simulation model A downward TGF triggering photonuclear reactions comprised 10 18 to 10 19 avalanche electrons produced at 1.4–2.7 km above sea level