Gamma-ray observations at 20 km altitude above thunderstorms

In the spring of 2017 the «GOES-R Validation Flight Campaign» was undertaken with an ER-2 aircraft over the continental United States. The scientific target of the campaign was validation of observations by the Advanced Baseline Imager (ABI) and Geostationary Lightning Mapper (GLM) instruments onboard the recently launched GOES-R satellite and, simultaneously, observation of energetic radiation from thunderstorms and lightning. The scientific payload consisted of a suite of instruments designed to detect optical signals, electric fields and gamma rays from lightning. Starting from Georgia, USA, a total of 11 flights were performed, for a total of about 70 flight hours at a cruise altitude of 20 km. Flying at this altitude and being directly over active thunderstorms should be optimal to detect intense terrestrial gamma-ray flashes (TGFs). These observations were the first of their kind. In a preliminary search through the data we found no clear evidence of intense TGFs, but further analysis is required. Clear signatures of gamma-ray glows are seen. In this paper we will present a more thorough analysis of the gamma-ray observations during the campaign.