CEDAR: Mechanisms and Effects of Terrestrial Gamma-Ray Flashes

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A 3-year theoretical investigation of the mechanisms and effects of Terrestrial Gamma-ray Flashes (TGFs) will be carried out under this grant. Recent observations of TGFs from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft have demonstrated the need for a revision of the current model for their generation. This project will investigate a new mechanism for the production of TGFs based on the possibility for production of runaway electron avalanche driven by electromagnetic impulses (EMP) radiated by rapidly moving lightning return strokes. The proposed program builds on previous models of TGF production developed by the proposing team and the main objective is to determine the quantitative feasibility of the EMP-driven mechanism. This includes the development of a kinetically based Monte Carlo model of the partially synchronized runaway acceleration of relativistic electrons by the lightning EMP. In addition, model results will be compared to experimental data, including TGF fluxes and energy spectra as observed on RHESSI.This project is cross-disciplinary in that it will advance understanding of the electrodynamic coupling between the lower (neutral) atmosphere, where thunderstorms occur, and the higher altitude ionized layers of the mesosphere and the ionosphere. In addition, relativistic runaway acceleration is a fundamentally new particle acceleration phenomenon and the results of this research project, therefore, will have broader scientific impact beyond atmospheric sciences.