Two first-author papers
– Photonuclear Reactions in Lightning: 1. Verification and Modeling of Reaction and Propagation Processes
– Photonuclear Reactions in Lightning: 2. Comparison Between Observation and Simulation Model
were published in the Journal of Geophysical Research: Atmospheres, a journal of the American Geophysical Union. The two papers were edited from a part of my doctoral dissertation and were published as a series.
In 2017, we detected neutrons and positrons in sync with a lightning discharge and found that the lightning discharge triggered a terrestrial gamma-ray flash, causing a photonuclear reaction in the atmosphere (Enoto et al. , Nature, 2017). Although this result revealed the mechanism of the photonuclear reactions caused by lightning discharge, on the other hand, the number of gamma rays, neutrons, and positrons emitted was not quantitatively evaluated. In the first paper, we modeled the terrestrial gamma-ray flash and described a series of processes from scatterings of gamma rays in the atmosphere, generation of photonuclear reactions, and propagation of neutrons and positrons in the atmosphere by Monte Carlo simulations with Geant4. In the second paper, we incorporated the detector response into the model obtained in the first paper and compared it with the actual observation data. As a result, we found that the amounts of each component of the terrestrial gamma-ray flash, neutrons, and positrons are consistent with the model and can be explained quantitatively by the photonuclear reactions. It was also found that the terrestrial gamma-ray flash emitted the same amount of gamma rays as those observed in space. It is generally thought that electrons are less likely to be accelerated near the ground, where the atmospheric pressure is higher than in space, but this result suggests a mechanism by which electrons are efficiently accelerated and amplified regardless of the density of the atmosphere.