TGFs, Gamma‐Ray Glows, and Direct Lightning Strike Radiation Observed During a Single Flight of a Balloon‐Borne Gamma‐Ray Spectrometer

Helmerich, Christopher; McKinney, Todd; Cavanaugh, Everett; Dangelo, Sarah

doi:10.1029/2023ea003317

Cited by 2 publications

References 68 publications

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Thunderstorm ground enhancements in Finland: observations using spectroscopic radiation detectors

Leppänen,

Peräjärvi,

Paatero

et al. 2024

Acta Geophys.

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This study reports observations of Thunderstorm Ground Enhancements (TGE) that occurred in Southern Finland in the Municipality of Vantaa (60° 18’ N 24° 58’ E at 55 m a.m.s.l) on May 17th, 2020 between 10:23 and 10:28 UTC. The TGEs occurred when a storm front moved across the Helsinki region from roughly a southwest to northeast direction. The TGEs were caused by a Runaway Relativistic Electron Avalanche (RREA) occurring inside a thundercloud. Three independent measuring units of high-volume NaI(Tl) γ spectrometers were used to record ambient dose rate and γ spectra. The observed TGEs manifested themselves as sudden increases in γ radiation on the ground with a wide range of energies from 100 keV up to the maximum of the detector system of 8.8 MeV. The first event lasted 50 s and produced an increase in γ radiation of about 7–12% in the spectra measured with a ten-second collection time. The enhancement in γ radiation was terminated suddenly and simultaneously with an in-cloud lightning strike. This was followed by an 88–100 s long period when the level of γ radiation returned to normal values. After this, a second enhancement was observed to increase the level of γ radiation by 20–50%. The second enhancement lasted 100 s and it was also terminated simultaneously with an in-cloud lightning flash. The second enhancement appears to be stronger, but the exact locations of the thundercloud emitting the γ radiation were not known. From the duration of the second enhancement and the prevailing wind speed, the size of the RREA was estimated to be 400–1000 m. In the second enhancement, the most intense increase was between 100 and 1000 keV, although very-high-energy γ rays was observed up to 8.8 MeV. The shape of the background-subtracted γ spectra agreed well with the observations and predictions of the shape of the bremsstrahlung spectrum emitted by an RREA. Additionally, in the background-subtracted spectra, a minor enhancement of the 511 keV peak was also observed where the RREA also increased the number of positrons which annihilated and increased the emission of the 511 keV γ rays. The results of these high-latitude, low-altitude TGE events are the first ones report in Finland.

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Thunderstorm ground enhancements in Finland: observations using spectroscopic radiation detectors

Leppänen,

Peräjärvi,

Paatero

et al. 2024

Acta Geophys.

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High latitude observations of Terrestrial Gamma-Ray Glow in Finland with spectroscopic radiation detectors

Leppänen,

Peräjärvi,

Paatero

et al. 2024

Preprint

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Terrestrial Gamma Glow (TGG) was detected for the first time in high latitudes outside the latitudinal band of ± 38° where Terrestrial Gamma Flashes (TGF) are typically observed. This study reports the observations of a TGG events that occurred in Southern Finland at the municipality of Vantaa (60° 18’ N 24° 58’ E at 55 m a.m.s.l) on May 17th, 2020 between 10:15 and 10:30 UTC. Three independently measuring units of NaI(Tl) γ spectrometers were used when a thundercloud emitting the γ radiation passed over or near the location of the detectors. The events occurred when a storm front moved across the Helsinki region in Finland in a roughly northeast direction. Two separate the γ radiation enhancements were observed. The first event lasted 52 s. and produced an increase in γ radiation of about 7 -12 %, after a break of about 85 -100 s., a second event occurred lasting about 100 s increasing the γ radiation by 20-50 % during the 10-second collection time. The exact locations of the thunderclouds emitting the γ radiation were not known and it is possible that the first event occurred farther away from the detectors and was hence seen as a weaker enhancement. The horizontal size was estimated by using the average wind speed and the duration of the second enhancement. The size estimate was around 400-500 m with maximum upper limit of 1000 m. In the second enhancement most visible increase in the γ radiation was in the 100 keV - ~800 keV energy range where a uniform increase was observed. In addition, a clear enhancement in the high energy γ rays, with energies from 3000 keV up to the maximum of the detector system of 8900 keV, was also observed. The presence of high energy γ rays is a clear signals of a TGG event. The shape of the background subtracted γ spectrum has a power law shape and agreed well with that of a predicted photon spectrum produced by a Runaway Relativistic Electron Avalanche.

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TGFs, Gamma‐Ray Glows, and Direct Lightning Strike Radiation Observed During a Single Flight of a Balloon‐Borne Gamma‐Ray Spectrometer

Cited by 2 publications

References 68 publications

Thunderstorm ground enhancements in Finland: observations using spectroscopic radiation detectors

Thunderstorm ground enhancements in Finland: observations using spectroscopic radiation detectors

High latitude observations of Terrestrial Gamma-Ray Glow in Finland with spectroscopic radiation detectors

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