Constraining Downward Terrestrial Gamma Ray Flashes Using Ground‐Based Particle Detector Arrays

Until recently, there were only a few ground‐based observations of terrestrial gamma ray flashes (TGFs). Since the Telescope Array in Utah, USA, started reporting detections of high‐energy particles correlated with lightning, their number has greatly increased. Ground observations of TGFs represent a valuable addition to space‐borne detectors. The proximity to the event and the ability to observe an event with several detectors may reveal new information about the production of TGFs. In this paper, we study downward directed TGFs using Monte Carlo modeling of photon transport through the atmosphere. The Telescope Array‐observed pulses of gamma rays spread over periods of a few hundred microseconds. We predict such structures to be observable at satellite altitude, given sufficient time resolution. Additionally, we demonstrate how various source spectra would lead to different number of photons reaching ground, which impacts the conclusions one can draw using observational data. Plain Language Summary Terrestrial gamma ray flashes (TGFs) are bursts of high‐energy photons that originate in thunderstorms. TGFs have been routinely observed from space since their discovery. Until recently, there were only a few ground‐based observations of TGFs. Their number has increased since the Telescope Array started reporting detections of high‐energy particles at the same time as lightning. Ground observations of TGFs represent a valuable addition to detectors in space. They are closer to the source of the event, and it is possible to observe a single event with several detectors. Because of this, ground observations may reveal new information about the production mechanisms of TGFs. We study downward TGFs by modeling photons moving through the atmosphere. The Telescope Array‐observed pulses of gamma rays. We predict that similar pulses should be observable by satellites, given sufficient time resolution. TGFs are thought to start out as photons moving in a cone‐shaped beam. We want to find the shape of this beam from ground observations, but photons interacting with the atmosphere changes how the beam looks. We determine the beam shape by the photons' positions on ground. We also find that the number of photons reaching ground is dependent on the photons' initial energies. Key Points We model downward directed TGFs in order to be able to better interpret ground observations We compare impulse responses at ground and satellite and identify beam geometries on ground The n