Constraints on terrestrial gamma ray flash production from satellite observation

Terrestrial gamma-ray flash (TGF) production has been modeled by several emission mechanisms. In spite of extensive studies of these mechanisms and the existing satellite data, significant uncertainties exist about the nature of the source. In this paper, we present a method to develop approximate production-mechanism-independent constraints on TGF production on the basis of Monte Carlo simulation of gamma-ray propagation through the atmosphere. A broad range of possible source parameters are simulated, based on assumptions of a simplified source with varying general properties. The results of the simulations are compared with averaged satellite data, from which constraints are derived. Constraints on the basis of photon fluence and spectral shape are presented and indicate a source of 10(3) - 10(5) J at an altitude of 15 - 20 km. Possible constraints based on the lateral distance between the location of TGF production and the spacecraft nadir point is also discussed.