Relativistic Runaway Electron Avalanches Within Complex Thunderstorm Electric Field Structures

Abstract

High-energy radiation originating from thunderclouds can be registered by detectors on satellites and on the ground surface. Intense bursts of photons with energy 10 keV-100 MeV lasting 0.1-5 ms are called terrestrial gamma ray flashes (TGFs) and are usually observed from satellites (Fishman et al., 1994;Mailyan et al., 2016;Østgaard et al., 2019). Thunderstorm ground enhancements (TGEs) and gamma ray glows can be observed under thunderclouds and have a duration of up to several hours (Chilingarian, 2011;A. Gurevich et al., 2016;Torii et al., 2009). The gamma-radiation of thunderclouds is caused by bremsstrahlung of runaway electrons, which accelerate and multiply in the electric field, forming relativistic runaway electron avalanches (RREAs) (

The criterion for infinite positron feedback in dynamics of relativistic runaway electron avalanches

“…Carlo simulations [5,24]. [5] proposed that the feedback coefficient is proportional to exp L λ RREA , where L -electric field region length, λ RREA -RREA exponential growth length, which can be used as a tool to extrapolate infinite feedback conditions [22]. Nevertheless, an analytical model is required for a complete understanding of relativistic feedback physics.…”

“…RREAs dynamics with positron feedback within a region with uniform critical electric field can be described step by step via a relatively simple onedimensional kinetic approach. A a RREA-accelerating region within a thunderstorm is called a cell [22]. If a RREA starts at the point z 0 from a single seed relativistic electron then its dynamics can be described, on average, as follows [4,5,15]: Here, N RREA (z, z 0 ) -number of runaway electrons at the point z within a RREA starting from the point z 0 (Figure 1 (a)).…”

“…It has been shown that gamma-ray process lengths do not depend on the electric field value while they depend on the air density hyperbolically, as 1 ρ , where ρ is the air density [22]. This can be generally applied to processes, which are not related to the electric field directly, for example, positron annihilation length.…”

“…Gamma decay length for 10 km altitude is approximately 1750 m [22]. Therefore, the formula is as follows:…”

“…A numerical solution of a kinetic equation considering relativistic feedback has been presented in [16,21]. RREAs physics in complex thunderstorm electric filed structures was firstly studied in [22,23].…”