Ground‐level observation of a terrestrial gamma ray flash initiated by a triggered lightning

Abstract

We report on a terrestrial gamma ray flash (TGF) that occurred on 15 August 2014 coincident with an altitude‐triggered lightning at the International Center for Lightning Research and Testing (ICLRT) in North Central Florida. The TGF was observed by a ground‐level network of gamma ray, close electric field, distant magnetic field, Lightning Mapping Array (LMA), optical, and radar measurements. Simultaneous gamma ray and LMA data indicate that the upward positive leader of the triggered lightning flash induced relativistic runaway electron avalanches when the leader tip was at about 3.5 km altitude, resulting in the observed TGF. Channel luminosity and electric field data show that there was an initial continuous current (ICC) pulse in the lightning channel to ground during the time of the TGF. Modeling of the observed ICC pulse electric fields measured at close range (100–200 m) indicates that the ICC pulse current had both a slow and fast component (full widths at half maximum of 235 μs and 59 μs) and that the fast component was more or less coincident with the TGF, suggesting a physical association between the relativistic runaway electron avalanches and the ICC pulse observed at ground. Our ICC pulse model reproduces moderately well the measured close electric fields at the ICLRT as well as three independent magnetic field measurements made about 250 km away. Radar and LMA data suggest that there was negative charge near the region in which the TGF was initiated.

Gamma Ray Signatures of Neutrons From a Terrestrial Gamma Ray Flash

“…The initial dip in the energy of this feature at~0.375 s is consistent with the detector's high voltage power supply sagging from the large current drawn by the PMT. Similar PMT sagging and dead time effects have been observed in a plastic and NaI(Tl) scintillator during a (Hare et al, 2016).…”

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

“…While astronomical satellites in near‐Earth orbits routinely detect TGFs beamed upward, on‐ground facilities have also detected similar phenomena but beamed downward, called downward TGFs. They have been observed with rocket‐triggered (Dwyer et al, ; Hare et al, ) and natural lightning discharges (Abbasi et al, , ; Colalillo, ; Dwyer et al, ; Tran et al, ). In particular, downward TGFs during winter thunderstorms are sometimes bright enough to produce a number of neutrons via photonuclear reactions (Babich, , ) close to the ground; thus, the neutrons and their byproducts can be observed by sea level measurements (Bowers et al, ; Enoto et al, ; Wada et al, , ).…”

Constraining Downward Terrestrial Gamma Ray Flashes Using Ground‐Based Particle Detector Arrays

“…Gamma ray flashes have also been observed from ground during Japanese winter thunderstorms (e.g., Enoto et al, ; Smith et al, ). While the observations by Dwyer et al (), Dwyer et al (), Enoto et al (), and Hare et al () were made by several detectors simultaneously, the total number of photons received was limited, and the events are few and far between. The number of ground observations of gamma ray flashes from thunderstorms increased significantly as unusual observations correlated to lightning activity were reported from the Telescope Array (TA) in Utah, USA (Abbasi et al, , ).…”