Optical emissions associated with terrestrial gamma ray flashes
Abstract
Terrestrial gamma ray flashes (TGFs) are high-energy photon bursts produced by high-energy
electrons originating in the Earth’s atmosphere through bremsstrahlung processes. In this paper, we present
modeling studies on optical emissions resulting from the excitation of air molecules produced by the
large population of electrons involved in TGF events based on two possible production mechanisms:
relativistic runaway electron avalanches (RREAs) and acceleration of thermal runaway electrons produced
by high-potential intracloud lightning leaders. Numerical models developed in this study are first validated
through the calculation of fluorescence emissions from air excited by energetic electrons and comparison
with available laboratory observations. Detailed discussion of the role of excitation and ionization collisions
on the formation of the electron energy distribution is presented. Moreover, using Monte Carlo simulations,
we show that electron energy distributions established from the two TGF production mechanisms
considered here are inherently different over the full energy range. The strong energy dependence of the
capability of electrons to generate excited states responsible for optical emissions from neutral and ionized
nitrogen molecules leads to intrinsic differences in optical emissions produced by different mechanisms
of TGF production. We also show that TGFs are most likely accompanied by detectable levels of optical
emissions and that the distinct optical features are of significant interest for constraining and validating
current TGF production models.
Fichier principal
Xu_et_al-2015-Journal_of_Geophysical_Research__Space_Physics.pdf (1.02 Mo)
Télécharger le fichier
Origin : Publisher files allowed on an open archive
Loading...