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Titel |
Optical Emissions Associated with Stepping Lightning Leaders in Cloud-to-Ground Lightning Flashes |
VerfasserIn |
Wei Xu, Sebastien Celestin, Victor Pasko |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250106515
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Publikation (Nr.) |
EGU/EGU2015-6190.pdf |
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Zusammenfassung |
Intense and brief bursts of X-ray emissions have been detected from the ground during
natural cloud-to-ground (CG) [Moore et al., GRL, 28, 2141-2144, 2001] and rocket-triggered
lightning flashes [Dwyer et al., Science, 299, 694-697, 2003]. The measurements at the
International Center for Lightning Research and Testing (ICLRT) have further revealed that
discrete and intense bursts of X-rays were closely correlated with the formation of leader
steps during CGs [Dwyer et al., GRL, 32, L01803, 2005]. The mechanism of relativistic
runaway electron avalanches (RREAs) in large-scale thunderstorm electric fields has been
ruled out for this energetic phenomenon as it is not capable of explaining the observed energy
spectra [Dwyer, GRL, 31, L12102, 2004]. On the other hand, Celestin and Pasko
[JGR, 116, A03315, 2011] have shown theoretically how the large flux of thermal
runaway electrons generated by streamers during the negative corona flash stage
of stepping lightning leaders could instead be responsible for these X-ray bursts
during negative CGs, and for terrestrial gamma-ray flashes (TGFs) [Fishman et al.,
Science, 264, 1313-1316, 1994] during intra-cloud lightning flashes (IC). In addition
to intense X-ray emissions, Stolzenburg et al. [JGR, 118, 2918-2937, 2013] have
suggested that the impulsive breakdown associated with initial leaders during the initial
breakdown (IB) stages of CGs and ICs can generate considerable amount of visible
light. The purpose of the present work is to quantify the optical emissions resulting
from the excitation of air molecules produced during the acceleration process of
thermal runaway electrons in the highly inhomogeneous electric field produced
around lightning leader tip region in negative CGs. For this purpose, a full energy
range Monte Carlo model combined with an optical emission model is employed to
simulate, from first principles, the dynamics of electrons in the energy range from
sub-eV to GeV and the subsequent generation of optical emissions by the large
ensemble of low- and high-energy electrons involved. We specifically investigate the
geometrical and optical features of the fluorescence light produced as corresponding
measurements could be used to probe the electrical properties of lightning leaders. |
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