Lightning leader altitude progression in terrestrial gamma‐ray flashes

Cummer, Steven A.; Lyu, Fanchao; Briggs, M. S.; Fitzpatrick, G.; Roberts, O. J.; Dwyer, J. R.

doi:10.1002/2015gl065228

Cited by 92 publications

(165 citation statements)

References 34 publications

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“…In the present paper, using satellite-measured photon fluence and corresponding best fit leader model, we have estimated this number in three steps. If we take the avalanche multiplication into account, most estimated numbers of seeds are consistent with previously reported estimations using measurements of radio signals and gamma-ray fluxes (e.g., Cummer et al, 2015;Dwyer et al, 2017). Second, we calculate the number of source bremsstrahlung photons that is required at the production altitude in order to reproduce the gamma-ray flux obtained in the first step.…”

Section: Notesupporting

confidence: 78%

Analysis of Individual Terrestrial Gamma‐Ray Flashes With Lightning Leader Models and Fermi Gamma‐Ray Burst Monitor Data

Mailyan

Célestin

et al. 2019

JGR Space Physics

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The Gamma‐ray Burst Monitor (GBM) onboard the Fermi spacecraft has observed many tens of sufficiently bright events, which are suitable for individual analysis. In our previous study, we fit individual, bright terrestrial gamma‐ray flashes (TGFs) with Relativistic Runaway Electron Avalanche (RREA) models for the first time. For relativistic‐feedback‐based models, the TGF‐producing electrons, which are seeded internally by a positive feedback effect, are usually accelerated in a large‐scale field with fully developed RREAs. Alternatively, lightning leader models may apply to either a large‐scale thunderstorm fields with fully developed RREAs or to inhomogeneous fields in front of lightning leaders where RREAs only develop partially. The predictions of the latter, inhomogeneous models for the TGF‐beaming geometry show some differences from estimations of the relativistic feedback models in homogeneous fields. In this work, we analyze a large sample of 66 bright Fermi GBM TGFs in the framework of lightning leader models, making comparisons with previous results from the homogeneous‐field RREA models. In most cases, the spectral analysis does not strongly favor one mechanism over the other, with 59% of the TGF events being best fit with the fully developed RREA mechanism, which corresponds to high‐potential leader models. The majority of the GBM‐measured TGFs can be best fit if the source altitude is below 15 km and 70% of events best fit by leader models cannot be satisfactorily modeled unless a tilted photon beam is used. For several spectrally soft TGFs, the tilted beam low‐potential leader model can best fit the data.

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Section: Notesupporting

confidence: 78%

Analysis of Individual Terrestrial Gamma‐Ray Flashes With Lightning Leader Models and Fermi Gamma‐Ray Burst Monitor Data

Mailyan

Célestin

et al. 2019

JGR Space Physics

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“…Cummer et al [] reported on three TGFs where in‐cloud lightning leaders preceding and following each TGF event were measured. The highest altitudes of the three pre‐TGF lightning pulses were 11.2, 8.3, and 9.4 km.…”

Section: Discussionmentioning

confidence: 99%

The spectroscopy of individual terrestrial gamma‐ray flashes: Constraining the source properties

et al. 2016

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We report on the spectral analysis of individual terrestrial gamma‐ray flashes (TGFs) observed with the Fermi Gamma‐ray Burst Monitor (GBM). The large GBM TGF sample provides 46 events suitable for individual spectral analysis: sufficiently bright, localized by ground‐based radio, and with the gamma rays reaching a detector unobstructed. These TGFs exhibit diverse spectral characteristics that are hidden when using summed analysis methods. We account for the low counts in individual TGFs by using Poisson likelihood, and we also consider instrumental effects. The data are fit with models obtained from Monte Carlo simulations of the large‐scale Relativistic Runaway Electron Avalanche (RREA) model, including propagation through the atmosphere. Source altitudes ranging from 11.6 to 20.2 km are simulated. Two beaming geometries were considered: In one, the photons retain the intrinsic distribution from scattering (narrow), and in the other, the photons are smeared into a wider beam (wide). Several TGFs are well fit only by narrow‐beam models, while others favor wide‐beam models. Large‐scale RREA models can accommodate both narrow and wide beams, with narrow beams suggest large‐scale RREA in organized electric fields while wide beams may imply converging or diverging electric fields. Wide beams are also consistent with acceleration in the electric fields of lightning leaders, but the TGFs that favor narrow‐beam models appear inconsistent with some lightning leader models.

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“…Those individual lightning discharges that have been both tied unequivocally to TGFs and categorized via well‐studied VLF emissions have been classified as positive intracloud (+IC) events [ Cummer et al , ; Stanley et al , ; Shao et al , ; Lu et al , , ], and most recently, it has been shown that the TGF appears as a distinctive radio signature during the upward propagation of a leader from the main negative to upper positive charge center [ Cummer et al , ; Dwyer and Cummer , ; Cummer et al , , ; Lyu et al , ]. Only a small fraction of lightning (much less than 1%) is creating TGFs that can be observed from space by current instruments [ Fuschino et al , ; Østgaard et al , ; Briggs et al , ; Tierney et al , ].…”

Section: Introductionmentioning

confidence: 99%

The rarity of terrestrial gamma‐ray flashes: 2. RHESSI stacking analysis

et al. 2016

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We searched for gamma‐ray emission from lightning using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite by identifying times when RHESSI was near over 2 million lightning discharges localized by the Worldwide Lightning Location Network (WWLLN). We then stacked together the gamma‐ray arrival times relative to the sferic times, correcting for light propagation time to the satellite. The resulting stacked gamma‐ray time profile is sensitive to an average level of gamma‐ray emission per lightning discharge far lower than what can be recognized above background for a single terrestrial gamma‐ray flash (TGF). The summed signal from presumed small, previously unknown TGFs simultaneous with WWLLN discharges is remarkably weak: for the region from 0 to 300 km beneath RHESSI's footprint, (6.2 ± 3.8) × 10−3 detector counts/discharge are measured, as opposed to a typical range of 12–50 detector counts for TGFs identified solely from the gamma‐ray signal. Under the assumption of a broken power law differential distribution of TGF intensities, we find that the index must harden dramatically or cut off just below the sensitivity limit of current satellites and that for most scenarios less than 1% of lightning can produce a TGF that belongs anywhere in the same distribution as those that are observable. For the minority of scenarios where more than a few percent of flashes produce a TGF, most of these “TGFs” are less than 10−4 of the luminosity of the faintest RHESSI TGFs and therefore closer to the luminosity of lightning stepped leaders. The rarity of TGFs holds not only for TGFs simultaneous with the sferic observed by WWLLN but also for any time within 10 ms of the sferic, allowing (for example) for the possibility that different events within the upward propagation of a negative leader in positive intracloud lightning triggered the TGF and WWLLN's detection.

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Lightning leader altitude progression in terrestrial gamma‐ray flashes

Cited by 92 publications

References 34 publications

Analysis of Individual Terrestrial Gamma‐Ray Flashes With Lightning Leader Models and Fermi Gamma‐Ray Burst Monitor Data

Analysis of Individual Terrestrial Gamma‐Ray Flashes With Lightning Leader Models and Fermi Gamma‐Ray Burst Monitor Data

The spectroscopy of individual terrestrial gamma‐ray flashes: Constraining the source properties

The rarity of terrestrial gamma‐ray flashes: 2. RHESSI stacking analysis

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