High-Energy Atmospheric Physics: Terrestrial Gamma-Ray Flashes and Related Phenomena

Dwyer, J. R.; Smith, David M.; Cummer, Steven A.

doi:10.1007/978-1-4614-6455-6_5

Cited by 103 publications

(186 citation statements)

References 216 publications

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“…In particular, the observations indicate that the TGFs occur within the first few milliseconds of upward intracloud (IC) flashes (Cummer et al, , ; Lu et al, ; Lyu et al, ; Shao et al, ; Stanley et al, ). Concurrently, the observations were found to be consistent with the relativistic runaway electron avalanche (RREA) model (Dwyer, , ; Dwyer & Smith, ; Dwyer, Smith, et al, ). In normally electrified storms, IC flashes occur between the main midlevel negative and the upper positive charge region.…”

Section: Introductionmentioning

confidence: 53%

Gamma Ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders

et al. 2018

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Bursts of gamma ray showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700-km 2 cosmic ray observatory located in southwestern Utah, USA. In data collected between 2014 and 2016, correlated observations showing the structure and temporal development of three shower-producing flashes were obtained with a 3-D lightning mapping array, and electric field change measurements were Key Points:• Gamma ray showers have been detected in a surface scintillator array coincident with lightning observed by a lightning mapping array or Delta E antenna • The showers were produced less than 4-5 km above ground in the first 1-2 ms of downward negative breakdown during cloud-to-ground flashes • The source durations are better resolved than for satellite observations and are consistent with being produced by stepping of the initial leader breakdown Supporting Information:• Supporting Information S1 obtained for an additional seven flashes, in both cases colocated with the TASD. National Lightning Detection Network information was also used throughout. The showers arrived in a sequence of 2-5 short-duration (≤10 s) bursts over time intervals of several hundred microseconds and originated at an altitude of ≃3-5 km above ground level during the first 1-2 ms of downward negative leader breakdown at the beginning of cloud-to-ground lightning flashes. The shower footprints, associated waveforms and the effect of atmospheric propagation indicate that the showers consist primarily of downward-beamed gamma radiation. This has been supported by GEANT simulation studies, which indicate primary source fluxes of ≃10 12 -10 14 photons for 16 ∘ half-angle beams. We conclude that the showers are terrestrial gamma ray flashes, similar to those observed by satellites, but that the ground-based observations are more representative of the temporal source activity and are also more sensitive than satellite observations, which detect only the most powerful terrestrial gamma ray flashes.

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Section: Introductionmentioning

confidence: 53%

Gamma Ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders

et al. 2018

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“…Correspondingly, the photon energy distribution produced by these electrons will have energies weaker than that of the electrons. A rough estimate of the average energy gain can be derived from equation [ Dwyer , ; Dwyer et al , ; Skeltved et al , ]. An average energy of 7.3 MeV, or less, of avalanche length can then be expected.…”

Section: Discussionmentioning

confidence: 99%

“…An extensive overview of TGF properties and related phenomena is found in Dwyer et al []. In this section we summarize the parameters that are important from the perspective of the production mechanisms.…”

Section: Properties Of Tgfs and Of Their Source Electronsmentioning

confidence: 99%

Constraints to do realistic modeling of the electric field ahead of the tip of a lightning leader

et al. 2017

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Several computer models exist to explain the observation of terrestrial gamma‐ray flashes (TGFs). Some of these models estimate the electric field ahead of lightning leaders and its effects on electron acceleration and multiplication. In this paper, we derive a new set of constraints to do more realistic modeling. We determine initial conditions based on in situ measurements of electric field and vertical separation between the main charge layers of thunderclouds. A maximum electric field strength of 50 kV/cm at sea level is introduced as the upper constraint for the leader electric field. The threshold for electron avalanches to develop of 2.86 kV/cm at sea level is introduced as the lower value. With these constraints, we determine a region where acceleration and multiplication of electrons occur. The maximum potential difference in this region is found to be ∼52 MV, and the corresponding number of avalanche multiplication lengths is ∼3.5. We then quantify the effect of the ambient electric field compared to the leader field at the upper altitude of the negative tip. Finally, we argue that only leaders with the highest potential difference between its tips (∼600 MV) can be candidates for the production of TGFs. However, with the assumptions we have used, these cannot explain the observed maximum energies of at least 40 MeV. Open questions with regard to the temporal development of the streamer zone and its effect on the shape of the electric field remain.

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“…This study also has implications to lightning‐related phenomena such as the relativistic feedback discharges that are thought to produce Terrestrial Gamma‐ray Flashes (TGFs) [ Dwyer , ; Dwyer et al ., ; Liu and Dwyer , ]. Terrestrial gamma‐ray flashes are bursts of extremely high energy radiation coming from thunderclouds and have been observed from space [e.g., Fishman et al ., ] and from ground [ Dwyer et al ., ].…”

Section: Discussionmentioning

confidence: 99%

Streamer formation and branching from model hydrometeors in subbreakdown conditions inside thunderclouds

et al. 2015

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Electric field values measured inside thunderclouds have consistently been reported to be up to an order of magnitude lower than the value required for the conventional electrical breakdown of air. This result has made it difficult to explain how lightning frequently occurs in thunderclouds. A few different theories have been offered to explain the lightning initiation process, one of them being the theory of lightning initiation from hydrometeors. According to this theory, lightning can be initiated from electrical discharges originating around thundercloud water or ice particles in the measured thundercloud electric field. These particles, called hydrometeors, are believed to cause significant enhancement of the thundercloud electric field in their vicinity and then initiate streamers that are the precursor discharges for the hot lightning leader channel. Previously, Liu et al. (2012a) reported streamer formation from a model hydrometeor in an electric field value of half of the conventional breakdown threshold (E k ) for air. In this paper, we present modeling results for streamer formation in electric fields as low as one third of the breakdown threshold. According to our results, initiation of stable streamers from thundercloud hydrometeors in a 0.3E k electric field is possible, only if enhanced ambient ionization levels (e.g., the ionization created by corona discharges around the same or other nearby hydrometeors) are present ahead of the streamer. The magnitude and distribution of this ambient density may be a determining factor on whether the streamer branches, recovers after the prebranching stage, or continues propagating stably. We investigate the streamer branching behavior and characteristics and test a theory that has recently been proposed to explain this phenomenon. We find that the geometry of the streamer head plays an important role in the streamer branching phenomena. The fast radial movement of the maximum streamer head curvature, combined with the slow reduction of the maximum curvature value, eventually leads the streamer head to branching. Finally, we compare our modeling results with laboratory experiments and realistic thundercloud conditions and discuss the implications of this study to lightning initiation and other lightning-related phenomena.

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High-Energy Atmospheric Physics: Terrestrial Gamma-Ray Flashes and Related Phenomena

Cited by 103 publications

References 216 publications

Gamma Ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders

Gamma Ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders

Constraints to do realistic modeling of the electric field ahead of the tip of a lightning leader

Streamer formation and branching from model hydrometeors in subbreakdown conditions inside thunderclouds

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