Modeling Observed Fermi Terrestrial Gamma-ray Flashes

One of the great mysteries in the atmospheric sciences is the source of terrestrial gamma-ray flashes (TGFs). TGFs are short bursts of gamma-rays observed by satellites in low Earth orbit that come from the atmosphere with energies extending up to several tens of MeV. The Gamma-ray Burst Monitor (GBM) on board the Fermi spacecraft has detected more than 16 TGFs since its launch in 2008. The GBM detector utilizes twelve sodium iodide scintillators and two bismuth germinate scintillators. In this study, the observed TGFs will be modeled with the relativistic runaway electron avalanche (RREA) simulation developed by Dwyer at Florida Institute of Technology. The particles in the simulation will travel from the thundercloud region to the spacecraft, 565 km above the surface of the earth, which will allow us to model the geometry of the particle beams as they propagate through the atmosphere and inner magnetosphere to the GBM. These simulations will make it possible to study the energy spectra, time-intensity profiles, anisotropies and composition (electrons, positrons, or gamma-rays). The detector response functions will then be used to fit the model to the GBM data. Various source properties will be considered such as electric field strength, beaming geometries, and altitudes.