Characterizing the source properties of terrestrial gamma ray flashes. Issue 8 (24th August 2017)

• Record Type: Journal Article
• Authors: Dwyer, Joseph R.; Liu, Ningyu; Eric Grove, J.; Rassoul, Hamid; Smith, David M.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 8(2017)
• Page Start: 8915
• Page End: 8932
• Publication Date: 2017-08-24
• Subjects: Lightning -- Thunderstorms -- Terrestrial gamma ray flashes; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2017JA024141
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: 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 electrons (i.e., the total grammage) during a TGF, Ξ, 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 Ξ 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, a standard TGF gamma ray fluence, F 0 = 0.1 cm −2 above 100 keV for a spacecraft altitude of 500 km, and a standard total grammage, Ξ0 = 10 18 g/cm 2, 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 direct 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. Key Points: Monte Carlo simulations are used to relate the gamma ray fluences recorded by spacecraft with source properties of the TGF The total grammage of the TGF is introduced, allowing more meaningful comparisons of models and observations TGF radio, optical, and gamma ray emissions are predicted Plain Language Summary: Terrestrial gamma ray flashes (TGFs) are bright bursts of gamma rays, usually observed from space, that originate from thunderstorms in the Earth's atmosphere. Even though they were discovered 23 years ago, it is still not clear how they are generated inside thunderstorms. There is also considerable disagreement on how bright they are at the source, hindering efforts to model these events. In this paper, the results of Monte Carlo simulations of TGFs are presented. Key properties of TGFs inside thunderstorms are determined and predictions about the relationships between the gamma ray, optical, and radio emissions are made.