Photonuclear Reactions in Lightning: 2. Comparison Between Observation and Simulation Model

During a winter thunderstorm on 6 February 2017 in Japan, photonuclear reactions such as N-14(gamma, n)N-13 were triggered by a downward terrestrial gamma-ray flash (TGF), as reported by Enoto et al. (2017, ). 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, ). The observation and model consist of three components: annihilation gamma rays from positrons produced by beta(+)-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) x 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.