A Terrestrial Gamma-Ray Flash inside the Eyewall of Hurricane Patricia

On 23 October 2015 at ~1732 UTC, the Airborne Detector for Energetic Lightning Emissions (ADELE) flew through the eyewall of Hurricane Patricia aboard National Oceanic and Atmospheric Administration's Hurricane Hunter WP-3D Orion, observing the first terrestrial gamma-ray flash (TGF) ever seen in that context, and the first ever viewed from behind the forward direction of the main TGF gamma-ray burst. ADELE measured 184 counts of ionizing radiation within 150 μs, coincident with the detection of a nearby lightning flash. Lightning characteristics inferred from the associated radio signal and comparison of the gamma-ray energy spectrum to simulations suggests that this is the first observation of a reverse beam of positrons predicted by the leading TGF production model, relativistic runaway electron avalanches. This paper presents the first experimental evidence of a previously predicted second component of gamma-ray emission from TGFs. The brightest emission, commonly observed from orbit, is from the relativistic runaway electron avalanche bremsstrahlung; the second, fainter component reported here is from the bremsstrahlung of positrons propagating in the reverse direction. This reverse gamma-ray beam penetrates to low enough altitudes to allow ground-based detection of typical upward TGFs from mountain observatories.

Duke Scholars

Author Steven A. Cummer Electrical and Computer Engineering