In‐Flight Observation of Gamma Ray Glows by ILDAS

Abstract

An Airbus A340 aircraft flew over Northern Australia with the In‐Flight Lightning Damage Assessment System (ILDAS) installed onboard. A long‐duration gamma ray emission was detected. The most intense emission was observed at 12 km altitude and lasted for 20 s. Its intensity was 20 times the background counts, and it was abruptly terminated by a distant lightning flash. In this work we reconstruct the aircraft path and event timeline. The glow‐terminating flash triggered a discharge from the aircraft wing that was recorded by a video camera operating onboard. Another count rate increase was observed 6 min later and lasted for 30 s. The lightning activity as reported by ground networks in this region was analyzed. The measured spectra characteristics of the emission were estimated.

Gamma Ray Glow Observations at 20‐km Altitude

“…From the time profile one could argue that there might be more than one source for these gamma ray enhancements. The rapid increase and drop in intensity between 21:47:15 and 21:47:30 UT (45% increase in only 15 s) could be from a more localized (or transient) source than the longer but weaker glow from 21:46:30 to 21:48:10 UT (6–16% increase) and the second glow from 21:49:30 to 21:50:30 UT (10%), which both might originate from a static structures we fly in and out of, similar to the structure reported by Kochkin et al (). During the time we observe the increased gamma rays we were flying at constant magnetic latitude so the increase in gamma ray intensity cannot be explained by less magnetic shielding at higher magnetic latitudes.…”

High Peak‐Current Lightning Discharges Associated With Downward Terrestrial Gamma‐Ray Flashes

“…They are thought to originate from bremsstrahlung of relativistic electrons accelerated and multiplied in large-scale electrified regions. They have been observed near thunderclouds by airborne experiments (Eack et al, 1996;Kelley et al, 2015;Kochkin et al, 2017;McCarthy & Parks, 1985;Parks et al, 1981) and mountain-top experiments (Alexeenko et al, 2002;Bowers et al, 2019;Chilingarian et al, 2010Chilingarian et al, , 2011Chilingarian et al, , 2016Torii et al, 2009;Tsuchiya et al, 2009Tsuchiya et al, , 2012. Since cloud bases are lower during winter thunderstorms in coastal areas of Japan Sea than summer (Goto & Narita, 1992;Kitagawa & Michimoto, 1994), gamma-ray glows become detectable even by sea level experiments (Kuroda et al, 2016;Torii et al, 2002Torii et al, , 2011Tsuchiya et al, 2007Tsuchiya et al, , 2011Tsuchiya et al, , 2013Wada et al, 2018).…”

“…Since cloud bases are lower during winter thunderstorms in coastal areas of Japan Sea than summer (Goto & Narita, 1992;Kitagawa & Michimoto, 1994), gamma-ray glows become detectable even by sea level experiments (Kuroda et al, 2016;Torii et al, 2002Torii et al, , 2011Tsuchiya et al, 2007Tsuchiya et al, , 2011Tsuchiya et al, , 2013Wada et al, 2018). They sometimes terminate with lightning discharges (Alexeenko et al, 2002;Chilingarian et al, 2015Chilingarian et al, , 2017Eack et al, 1996, Kelley et al, 2015Kochkin et al, 2017;McCarthy & Parks, 1985;Tsuchiya et al, 2013;Wada et al, 2018), and a part of them also coincided with downward TGFs (Smith et al, 2018;Wada et al, 2019a).…”

Origin of enhanced gamma radiation in thunderclouds

“…Seed electrons from an ambient population of cosmic rays are accelerated in the strong electric field forming an electrongamma ray avalanche, directed either downwards to the Earth's surface or upwards into the open space, depending on the direction of the electric field. Intense fluxes of gamma rays observed in space are called terrestrial gamma flashes (TGFs) [3][4][5]; the ones in the atmosphere are called gamma glows [6][7][8][9], and the ones that are observed on the ground are called thunderstorm ground enhancements (TGEs) [10][11][12][13][14][15][16]. In the latter, also neutron fluxes are observed [17][18][19][20].…”