Measurements of x‐ray emission from rocket‐triggered lightning

Dwyer, J. R.; Rassoul, H. K.; Al‐Dayeh, M.; Caraway, L.; Wright, Brian D.; Chrest, A.; Uman, M. A.; Rakov, Vladimir A.; Rambo, K. J.; Jordan, D. M.; Jerauld, J.; Smyth, C. Piazzi

doi:10.1029/2003gl018770

Cited by 105 publications

(148 citation statements)

References 12 publications

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“…Figure 21, from Dwyer and Smith (2005), shows the RHESSI summed TGF spectrum along with the relativistic runaway (REAM) model at several altitudes, demonstrating that even TGFs deep in the atmosphere produce significant flux <100 keV, and that the best diagnostic of depth comes from the spectral slope in the range of approximately 0.5 MeV to 4 MeV. A comparison of the RHESSI TGF spectrum and the ground-level event seen by Dwyer et al (2004a) can be found in Dwyer (2009).…”

Section: Tgf Spectra and Source Altitudementioning

confidence: 92%

“…3.3). Carlson et al (2010b) note that neutrons seen from the ground due to a downwarddirected TGF should be accompanied by a detectable level of gamma-rays above 10 MeV, a phenomenon that has only been observed once, in triggered lightning (Dwyer et al 2004a). …”

Section: Interpretation Of Neutron Observationsmentioning

confidence: 99%

“…In 2004, it was generally believed that RREA was responsible for the x-ray emissions from natural and triggered lightning. However, Dwyer (2004), using the Dwyer et al (2004b) measurements, showed that the fluence and energy spectra of the xray emissions from triggered lightning were not consistent with the RREA mechanism and Dwyer et al (2004b) proposed that instead the thermal runaway electron mechanism (Gurevich 1961) was responsible for the emissions. Later, Moss et al (2006) modeled the thermal runaway electron production by streamers, and showed that significant runaway electron production was plausible.…”

Section: Detailed Investigationsmentioning

confidence: 99%

“…Dwyer et al (2004b) showed that the detected energetic radiation was predominantly x-rays with energies usually extending up to about 250 keV and that the x-rays were emitted in discrete bursts lasting less than 1 µs during the dart leader and dart-stepped leader phases and possibly at the beginning of the return strokes of negative triggered lightning. Dwyer et al (2004b) also showed that x-ray emissions originated from the bottom few hundred meters of the leader channel and that the source propagated downward with the leader as it approached the ground.…”

Section: Detailed Investigationsmentioning

confidence: 99%

“…Later discoveries overturned this presumed association (see Sect. 4.4 below): In 2004, Dwyer et al (2004a) reported a gamma-ray flash observed on the ground in Florida in association with rocket-triggered lightning. The event, which seemed to have originated from the overhead thundercloud, had an energy spectrum and duration similar to TGFs.…”

Section: Observations Of Terrestrial Gamma-ray Flashes: the Batse Eramentioning

confidence: 99%

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

2012

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It is now well established that both thunderclouds and lightning routinely emit x-rays and gamma-rays. These emissions appear over wide timescales, ranging from submicrosecond bursts of x-rays associated with lightning leaders, to sub-millisecond bursts of gamma-rays seen in space called terrestrial gamma-ray flashes, to minute long glows from thunderclouds seen on the ground and in or near the cloud by aircraft and balloons. In particular, terrestrial gamma-ray flashes (TGFs), which are thought to be emitted by thunderclouds, are so bright that they sometimes saturate detectors on spacecraft hundreds of kilometers away. These TGFs also generate energetic secondary electrons and positrons that are detected by spacecraft in the inner magnetosphere. It is generally believed that these x-ray and gamma-ray emissions are generated, via bremsstrahlung, by energetic runaway electrons that are accelerated by electric fields in the atmosphere. In this paper, we review this newly emerging field of High-Energy Atmospheric Physics, including the production of runaway electrons, the production and propagation of energetic radiation, and the effects of both on atmospheric electrodynamics.

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Section: Tgf Spectra and Source Altitudementioning

confidence: 92%

Section: Interpretation Of Neutron Observationsmentioning

confidence: 99%

Section: Detailed Investigationsmentioning

confidence: 99%

Section: Detailed Investigationsmentioning

confidence: 99%

Section: Observations Of Terrestrial Gamma-ray Flashes: the Batse Eramentioning

confidence: 99%

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

2012

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The angular distribution of energetic electron and X‐ray emissions from triggered lightning leaders

et al. 2013

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[1] We investigate individual X-ray bursts from lightning leaders to determine if energetic electrons at the source (and hence X-rays) are emitted isotropically or with some degree of anisotropy. This study was motivated by the work of Saleh et al. (2009), which found the falloff of X-rays in concentric radial annuli, covering all azimuthal directions in each annulus, from the lightning channel to be most consistent with an isotropic electron source. Here we perform a statistical analysis of angular and spatial distributions of X-rays measured by up to 21 NaI/PMT detectors at the International Center for Lightning Research and Testing site for 21 leader X-ray bursts from five leaders (including four dart-stepped leaders and one dart leader). Two procedures were used to complete this analysis. Procedure 1 found the first-order anisotropy, and procedure 2 tested whether or not the angular distribution was consistent with an isotropic distribution. Because higher-order anisotropies could be present in the data, a distribution that is not isotropic does not necessarily have a significant first-order anisotropy. Using these procedures, we find that at least 11 out of 21 X-ray bursts have a statistically significant first-order anisotropy, and hence those 11 are inconsistent with an isotropic emission. The remaining 10 bursts do not have significant first-order anisotropy. However, of those 10 bursts, 9 are inconsistent with isotropic emission, since they exhibit significant higher-order anisotropies. Since Saleh et al. (2009) did not consider anisotropies in the azimuthal direction, these new measurements of anisotropy do not necessarily contradict that work. Indeed, our analysis supports the finding that the X-ray emissions from lightning are inconsistent with a vertically downward beam. The level of anisotropy of the runaway electrons is important because it provides, in principle, information on the streamer zone in front of the leader and the electric field near the lightning leader tip.

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Modeling of X‐ray emissions produced by stepping lightning leaders

Célestin

Pasko

2014

Geophysical Research Letters

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Intense and brief bursts of X-ray emissions have been measured during the stepping process of both natural cloud-to-ground (CG) and rocket-triggered lightning flashes. In this paper, we investigate theoretically the energy spectra of X-rays produced by the bremsstrahlung emission of thermal runaway electrons accelerated in the inhomogeneous electric field produced around lightning leader tips. The X-ray energy spectrum depends on the physical properties of the associated lightning leaders. Consequently, X-ray measurements can be used for diagnostics of the electrical properties of lightning stepped leaders. We report simulation results of the photon energy spectra produced by 5 and 10 MV negative CG lightning discharges that would be measured from the ground using ideal detectors. We also quantify theoretically the radial dependence of X-ray energy spectra received at ground level during the leader stepping process. Moreover, it is found that the ground radiation generated in this process is harmless to humans.

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Measurements of x‐ray emission from rocket‐triggered lightning

Cited by 105 publications

References 12 publications

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

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

The angular distribution of energetic electron and X‐ray emissions from triggered lightning leaders

Modeling of X‐ray emissions produced by stepping lightning leaders

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