On the origin of the particle fluxes from the thunderclouds: Energy spectra analysis

Abstract

Simultaneous measurements of the gamma ray differential energy spectra, electric field disturbances, and meteorological conditions provided by experimental facilities located at Mt. Aragats in Armenia allows to establish the model of particle acceleration and propagation in thunderstorm atmosphere. We present comparisons of measured and modeled thunderstorm ground enhancements (TGEs). The origin of the majority of TGEs is the MOS process -the modification of energy spectra of cosmic ray electrons in the atmospheric electric fields. The gamma ray differential energy spectra are well described by the power law function with indexes in the range −1.5 ÷ −2.5 for the electric field strengths 0.8-1.5 kV/cm at altitudes of 3400-5000 m a.s.l. The good agreement of the characteristics of experimental and simulated TGEs gives hope to estimate the intracloud electric field by the observed parameters of TGE gamma ray energy spectra.

Gamma Ray Glow Observations at 20‐km Altitude

“…For these locations we will consider two mechanisms for producing the glow and in both cases we assume that it is the cosmic background flux that is enhanced. The first one is similar to the MOS mechanism suggested by Chilingarian et al (, ) for explaining the Thunderstorm Ground Enhancements but here applied to higher altitudes. This idea builds on the ideas suggested earlier by McCarthy and Parks () to explain the first glow observations from the early 1980s (McCarthy & Parks, ; Parks et al, ).…”

“…This mechanism requires field strength of just a fraction of E t but gives the cosmic background electron and positron sufficient extra energy to produce enhanced fluxes of gamma rays. The spectral shape resulting from RREA and MOS was also investigated by Cramer et al () who found similar spectral behavior as reported by Chilingarian et al ().…”

“…Gamma ray enhancements of 50–100% above background level for >1 min were observed at sea level in Japan during winter storms (Tsuchiya et al, , ), while Chilingarian et al () and Chilingarian () reported enhancements usually of a few percentage, but occasionally up to 100%, above the background level that were detected at the Aragats Mountain in Armenia, 3,200 m above sea level, and lasting for several minutes. Chilingarian et al () termed their observations Thunderstorm Ground Enhancements, and in a few modeling papers (Chilingarian et al, , ) they found strong support for the Modification Of Spectra (MOS) process as the production mechanism. This mechanism requires field strength of just a fraction of E t but gives the cosmic background electron and positron sufficient extra energy to produce enhanced fluxes of gamma rays.…”

A simulation study on the electric field spectral dependence of thunderstorm ground enhancements and gamma ray glows

“…Cramer et al [] found that as the electric field approaches the runaway electron threshold value, the solution to the electron energy spectrum is a convolution between a power law function and a Gaussian distribution [see Cramer et al , , equation (39)]. At the same time, it is worth mentioning that even if the power law fits seem not to be correct at relatively high fields above δ = 1.05, as it was shown by Chilingarian et al [, ], most of the measured TGEs correspond to lower field cases, where power law still applies. Moreover, it was shown that most of the TGEs or glows occur under fields below the runaway threshold, so called Modification of Spectra (MOS) process [ Chilingarian et al , ].…”

“…For most of the TGE glows, only gamma ray spectra are possible to estimate. At the same time, the estimations of Chilingarian et al [] showed that some of the events correspond to cases where the electric fields are lower than the critical field necessary for the RREA initiation. This process is termed Modification of Spectra (MOS), when secondary cosmic ray electron spectra are modified without an avalanche multiplication process earlier suggested by Chilingarian et al [].…”