Electric field change measurements of a terrestrial gamma ray flash

Abstract

The electric field change (E-change) data presented herein provide a complementary view of a known terrestrial gamma ray flash (TGF), namely, TGF1 from Cummer et al. (2014). The main E-change pulse coincident with TGF1 was likely an initial breakdown (IB) pulse of an intracloud (IC) flash since it had the typical characteristics of such an IC IB pulse: a bipolar shape with a positive leading peak and a duration of 47 µs. The IB pulse was especially energetic, with an estimated zero-to-peak amplitude between 36 and 47 V/m range normalized to 100 km (compared to an average IC IB pulse amplitude of ~1.5 V/m). The positive peak of the IB pulse occurred 19 µs after the beginning of the pulse. The first and most energetic gamma ray (7.6 MeV) detected in TGF1 occurred at 9 ± 10 µs after the beginning of the IB pulse. Thus, at the earliest the first detected gamma ray may have been produced just before or at the beginning of the IB pulse; at the latest, it may have been produced at the peak of the IB pulse.