Accession Number : AD1024088

Title :   Comparison of Terrestrial Gamma Ray Flash Simulations with Observations by Fermi

Descriptive Note : Technical Report,05 Aug 2015,04 Aug 2016

Corporate Author : University of New Hampshire Durham United States

Personal Author(s) : Dwyer,Joseph R

Full Text :

Report Date : 31 Oct 2016

Pagination or Media Count : 4

Abstract : For this project Monte Carlo simulations of terrestrial gamma rays flashes (TGFs) were preformed and results compared with spacecraft observations, including results from Fermi, and other simulations. As a result of this work, a paper has been written and will be submitted to the Journal of Geophysical Research-Space (Dwyer et al. 2016). For this paper, Monte Carlo simulations are used to determine source properties of terrestrial gamma-ray flashes (TGFs) as a function of atmospheric column depth and beaming geometry. The total mass per unit area traversed by all the runaway elections (i.e., the total grammage) during a TGF, Xi, is introduced, defined to be the total distance traveled by all the runaway electrons along the electric field lines multiplied by the local air mass density along their paths. It is shown that key properties of TGFs may be directly calculated from Xi and its time derivative, including the gamma-ray emission rate, the current moment, and the optical power of the TGF. For the calculations presented in this paper, the standard TGF gamma-ray fluence F(0) = 0.1 cm( -2) for a spacecraft altitude of 500 km and the standard total grammage Xi(0) = 10(18) g/cm2 are introduced, and results are presented in terms of these values. In particular, the current moments caused by the runaway electrons and their accompanying ionization are found for a standard TGF fluence, as a function of source altitude and beaming geometry, allowing a direction comparison between the gamma rays measured in low-Earth orbit and the VLF-LF radio frequency emissions recorded on the ground. Such comparisons should help test and constrain TGF models and help identify the roles of lightning leaders and streamers in the production of TGFs.

Descriptors :   gamma rays , emission , Thunderstorms , monte carlo method , lightning

Subject Categories : Atmospheric Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE