Detecting an Upward Terrestrial Gamma Ray Flash from its Reverse Positron Beam

Ortberg, J.; Smith, David M.; Li, Joseph; Dwyer, J. R.; Bowers, G. S.

doi:10.1029/2019jd030942

Cited by 8 publications

(12 citation statements)

References 39 publications

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“…Based on the RREA theory, the gamma rays produced by reverse positron beam have a harder spectrum (Bowers et al, 2018; Ortberg et al, 2020). In this case, the CG‐TGF produced 8 high‐energy BGO counts and 10 low‐energy NaI counts.…”

Section: Measurements and Analysismentioning

confidence: 99%

“…According to the electron atmospheric absorption formula of e ‐folding column density of 45 g cm −2 (Smith et al, 2010), a 7 km source altitude will produce 150X more attenuation than a typical upward TGF source altitude of 12 km. In addition, the backward positron beam has only about 1% of gammas in the main forward beam (Ortberg et al, 2020). However, the relatively narrow beamed and higher energy backward positron‐produced gamma rays (Bowers et al, 2018) may produce some gain.…”

Section: Measurements and Analysismentioning

confidence: 99%

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A Satellite‐Detected Terrestrial Gamma Ray Flash Produced by a Cloud‐to‐Ground Lightning Leader

Cummer

Huang

et al. 2020

Geophysical Research Letters

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We report measurements of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma‐ray Burst Monitor that was produced during a negative cloud‐to‐ground (CG) lightning leader. This is the first report of a downward directed TGF occurring during a CG flash but detected by a space‐based instrument. The gamma ray photons are produced 3 ms preceding a return stroke (−146 kA) and are essentially simultaneous with an isolated low frequency radio pulse. Based on timing, the pulse is estimated to initiate at approximately 6 km altitude, and its polarity indicates downward moving negative charge, the opposite of regular satellite‐detected upward TGFs. A likely scenario is that the runaway electrons accelerate into the upper, positively charged end of the leader in a high field region, with the reverse positron beam generating upward gamma rays detectable from space. A search for similar waveform features indicates that this type of downward CG‐TGF may occur prior to 1% of high peak current CG strokes. Extrapolating gives a global rate of 5–10% of previously known TGFs and potentially a significant fraction of global TGFs.

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Section: Measurements and Analysismentioning

confidence: 99%

Section: Measurements and Analysismentioning

confidence: 99%

A Satellite‐Detected Terrestrial Gamma Ray Flash Produced by a Cloud‐to‐Ground Lightning Leader

Cummer

Huang

et al. 2020

Geophysical Research Letters

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“…The reverse positron beam is expected to be ∼100 times weaker than the electron beam, reducing its detectability. Partially improving the detectability, the average gamma‐ray energy is higher and the beam narrower (Ortberg et al., 2020). The positron‐beam TGF detected by Fermi GBM is consistent with these predictions: The TGF was at the detection threshold of GBM, had a high‐energy gamma ray (>10 MeV) and was observed at the low offset of 117 km (Pu et al., 2020).…”

Section: Discussionmentioning

confidence: 99%

A Terrestrial Gamma‐Ray Flash From the 2022 Hunga Tonga–Hunga Ha'apai Volcanic Eruption

Briggs

Lesage

Schultz

et al. 2022

Geophysical Research Letters

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The Hunga Tonga–Hunga Ha'apai submarine volcano recently resumed activity. Violent eruptions on 14th and 15th January 2022 launched a tall ash plume that produced extremely high lightning rates. Here we report a terrestrial gamma‐ray flash (TGF) that was produced by the volcanic lightning and observed from space by the Fermi Gamma‐ray Burst Monitor (GBM). Observations by radio lightning networks and especially by the Geostationary Lightning Mapper show that the only lightning close enough to produce a TGF detectable by Fermi GBM was from the volcano's plume. With the observing duration of Fermi, observing a single TGF is consistent with the hypothesis that the volcanic lightning of this eruption produced TGFs at the average rate of thunderstorm lightning. The observation of a strong TGF from space also indicates that the electric field was oriented so as to accelerate electrons upward.

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“…Modeling work by Ortberg et al. (2020) suggests that upward TGFs observable from space can theoretically be coobserved from the ground if the ground observation point is at sufficient altitude, say a mountaintop.…”

Section: Introductionmentioning

confidence: 99%

“…Considering that a TGF would experience considerable absorption from a source altitude of 6 km and that the reverse beam TGF is understood to be roughly 1% the brightness of the main forward beam (Ortberg et al., 2020), is this observation under these circumstances possible? Can a reverse beam TGF be seen from space from so deep in the atmosphere, and how bright would the main (downward) TGF need to be?…”

Section: Introductionmentioning

confidence: 99%

Determining a Lower Limit of Luminosity for the First Satellite Observation of a Reverse Beam Terrestrial Gamma Ray Flash Associated With a Cloud to Ground Lightning Leader

Chaffin,

Pu,

Smith

et al. 2023

JGR Atmospheres

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We provide an updated analysis of the gamma ray signature of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma‐ray Burst Monitor first reported by Pu et al. (2020). A TGF produced 3 ms prior to a negative cloud‐to‐ground return stroke was close to simultaneous with an isolated low frequency radio pulse during the leader’s propagation, with a polarity indicating downward moving negative charge. In previous observations this ’slow’ low frequency signal has been strongly correlated with upward directed (opposite polarity) TGF events (Pu et al., 2019; Cummer et al., 2011), leading the authors to conclude that the Fermi gamma ray observation is actually the result of a reverse positron beam generating upward directed gamma rays. We investigate the feasibility of this scenario and determine a lower limit on the luminosity of the downward TGF from the perspective of gamma ray timing uncertainties, TGF Monte Carlo simulations, and meteorological analysis of a model storm cell and its possible charge structure altitudes. We determined that the most likely source altitude of the TGF reverse beam was 7.5 km ± 2.6 km, just below an estimated negative charge center at 8 km. At that altitude the Monte Carlo simulations indicate a lower luminosity limit of 2 × 1018 photons above 1 MeV for the main downward beam of the TGF, making the reverse beam detectable by the Fermi Gamma‐ray Burst Monitor.

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Detecting an Upward Terrestrial Gamma Ray Flash from its Reverse Positron Beam

Cited by 8 publications

References 39 publications

A Satellite‐Detected Terrestrial Gamma Ray Flash Produced by a Cloud‐to‐Ground Lightning Leader

A Satellite‐Detected Terrestrial Gamma Ray Flash Produced by a Cloud‐to‐Ground Lightning Leader

A Terrestrial Gamma‐Ray Flash From the 2022 Hunga Tonga–Hunga Ha'apai Volcanic Eruption

Determining a Lower Limit of Luminosity for the First Satellite Observation of a Reverse Beam Terrestrial Gamma Ray Flash Associated With a Cloud to Ground Lightning Leader

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