Terrestrial gamma-ray Flashes (TGFs) are intense, sub-millisecond bursts of gamma-rays routinely observed by satellites with energy spectra and timing characteristics consistent with bremsstrahlung from electron avalanches produced in thunderstorm electric fields. Since their discovery in 1994, the overwhelming majority of TGF observations have been from satellites. The goal of this work was to see how well TGFs could be observed from instruments on the ground or in the air, and whether there exist TGFs too dim to be seen from space, or TGF related phenomena impossible to observe from satellite.

Using portable instruments consisting of scintillation radiation detectors, we report on the ground observation of a 100 ms duration neutron flash from a lightning strike to a wind turbine in Japan, and evidence of positrons associated with lightning from observations aboard an airplane inside the eyewall of Hurricane Patricia. We discuss methods for deriving TGF brightness by comparing our observations to Monte Carlo simulations. Both the neutron flash seen in Japan, and the evidence for a downward beam of positrons produced in the eyewall of Hurricane Patricia are consistent with production from TGFs with brightnesses typical of TGFs so far observed from space.