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

Bowers, G. S.; Smith, David M.; Kelley, N. A.; Martinez-McKinney, G. F.; Cummer, S. A.; Dwyer, J. R.; Heckman, S.; Holzworth, R. H.; Marks, Frank D.; Reasor, Paul D.; Gamache, John F.; Dunion, Jason; Richards, T H; Rassoul, H. K.

doi:10.1029/2017jd027771

Cited by 26 publications

(20 citation statements)

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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%

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%

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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“…Different authors have used different standards to define the luminosity of a TGF; the values for the lower limits on TGF luminosity in the right‐hand columns of Table 2 can be converted as follows. To convert to photons >1 MeV (as used by Bowers et al, 2018), divide the number of photons >20 keV by a factor of 5.41. This is a characteristic of the generic RREA spectrum (Dwyer, 2003; Dwyer & Smith, 2005).…”

Section: “Paralyzing” Tgfs and Compton Tail Analysismentioning

confidence: 99%

Special Classes of Terrestrial Gamma Ray Flashes From RHESSI

Smith

Kelley²,

Buzbee

et al. 2020

JGR Atmospheres

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We report on three classes of terrestrial gamma ray flashes (TGFs) from the (RHESSI) satellite. The first class drives the detectors into paralysis, being observed usually through a few counts on the rising edge and the later tail of Comptonized photons. These events-and any bright TGF-reveal their true luminosity more clearly via their Compton tail than via the main peak, since the former is unaffected by the unknown beaming pattern of the unscattered radiation, and Comptonization mostly isotropizes the flux. This technique could be applied to TGFs from any mission. The second class is more than usually bright and long in duration. When the magnetic field at the conjugate point is stronger than at the nearby footpoint, we find that 4 out of 11 such events show a significant signal at the time expected for a relativistic electron beam to make a round trip to the opposite footpoint and back. We conclude that a large fraction of TGFs lasting more than a few hundred microseconds may include counts due to the upward moving secondary particle beam ejected from the atmosphere. Finally, using a new search algorithm to find short TGFs in RHESSI, we see that these tend to occur more often over the oceans than land, relative to longer-duration events. In the feedback model of TGF production, this suggests a higher thunderstorm potential, since more feedback per avalanche implies fewer "generations" of avalanches needed to complete the TGF discharge.

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“…The idea that a TGF could have a reverse beam due to positron bremsstrahlung has been known to be possible in theory given the simulations presented in Dwyer (), though the feasibility of detecting such a reverse beam has not been explored in detail. Recently Bowers et al () believe they observed this phenomenon in the eyewall of Hurricane Patricia in the 2015 season. A TGF was detected onboard an aircraft at 2.6 km altitude, but the radio signal for the associated lightning strike suggested an upward motion of electrons (and therefore upward‐directed TGF).…”

Section: Background and Summarymentioning

confidence: 92%

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

Ortberg

Smith

et al. 2020

JGR Atmospheres

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In 2015, Bowers et al. (2018, https://doi.org/10.1029/2017JD027771) detected a terrestrial gamma ray flash (TGF) in Hurricane Patricia from an aircraft flying at 2.6 km through what they argued to be a beam of downward gamma radiation produced by the positron component of the TGF. This paper uses the energy spectrum for gamma rays produced by the positrons of a relativistic runaway electron avalanche as simulated by the REAM code, propagated through a model of the Earth's atmosphere in Geant4, to examine the feasibility of detecting a typical upward TGF through its reverse positron beam at various altitudes on the ground. We find that, with patience, modest‐sized scintillators on mountains as low as 1 km should be able to observe the same TGFs seen from spacecraft.

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

Cited by 26 publications

References 50 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

Special Classes of Terrestrial Gamma Ray Flashes From RHESSI

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

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