Estimation of doses from electrons, photons, and secondary particles associated with TGFs
Résumé
In 1994, a new type of radiation coming from the Earth's atmosphere was discovered. This radiation, now known as terrestrial gamma-ray flashes (TGFs), comes in the form of bursts of high-energy photons, lasting less than one millisecond [Fishman et al., Science, 264, 1313, 1994]. Initially expected to be rare events, we now know that they are related to common thunderstorms [Chronis et al., BAMS, 97, 639, 2016 ; Splitt et al., JGR, 115, A00E38, 2010] and intra-cloud lightning discharges [e.g., Cummer et al., GRL, 42, 7792, 2015]. Briggs et al. [JGR, 118, 3805, 2013] estimate 400,000 TGFs per year, as detectable by the Fermi-Gamma ray Burst Monitor (GBM). Thunderstorms also produce another type of events, called gamma ray glows. These are significant elevations of the background radiation, lasting from seconds to minutes. Both are explained by the same phenomena: bremsstrahlung emission and relativistic runaway electron avalanche (RREA) [e.g., Kelley et al., Nat. Commun., 6, 7845, 2015 ; Wada et al., Comm. Phys., 2, 67, 2019]. A conservative estimate of the occurence of gamma-ray glows is that 8% of electrified storms produce them [Kelley et al., 2015]. Both TGFs [e.g., Cummer et al., GRL, 41, 8586, 2014] and gamma ray glows [e.g., Eack and Beasley, JGR, 120, 6887, 2015] are produced at thunderstorm altitudes, which calls for a precise assessment of the risk encountered by aircrew and passengers on a plane that would fly near or through thunderstorms. The exposure of aircrew is usually monitored by software that estimates the dose received for each individual, within the route flight data, taking into account the galactic component (cosmic rays) and relevant solar flares. Dwyer et al. [JGR, 115, A00E14, 2010] estimated the dose that a TGF could produce as a function of the diameter of the electron beam, and showed that TGFs could be an additional non negligible exposure for aircraft passengers. In this work, we will present calculations of doses produced by different parts and components of TGFs: RREA, gamma-rays and secondary particles, within the different theories of production (leader-based model [e.g., Xu et al., GRL, 39, L08801, 2012 ; Celestin et al., JGR, 120, 10, 712, 2015] and relativistic feedback model [e.g., Dwyer, JGR, 113, D10103, 2008]) that would be received by humans if an airplane were to find itself in such an event.