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| Titel |
Dimension of a fractal streamer structure |
| VerfasserIn |
Nikolai G. Lehtinen, Nikolai Østgaard |
| 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 |
250110452
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| Publikation (Nr.) |
 EGU/EGU2015-10449.pdf |
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| Zusammenfassung |
| Streamer corona plays an important role in formation of leader steps in lightning. In order to
understand its dynamics, the streamer front velocity is calculated in a 1D model with
curvature. We concentrate on the role of photoionization mechanism in the propagation
of the streamer ionization front, the other important mechanisms being electron
drift and electron diffusion. The results indicate, in particular, that the effect of
photoionization on the streamer velocity for both positive and negative streamers
is mostly determined by the photoionization length, with a weaker dependence
on the amount of photoionization, and that the velocity is decreased for positive
curvature, i.e., convex fronts. These results are used in a fractal model in which the front
propagation velocity is simulated as the cluster growth probability [Niemeyer et al,
1984, doi:10.1103/PhysRevLett.52.1033]. Monte Carlo simulations of the cluster
growth for various ratios of background electric field E to the breakdown field
Eb show that the emerging transverse size of the streamers is of the order of the
photoionization length, and at the larger scale the streamer structure is a fractal
similar to the one obtained in a diffusion-limited aggregation (DLA) system. In
the absence of electron attachment (Eb = 0), the fractal dimension is the same
(D ≈ 1.67) as in the DLA model, and is reduced, i.e., the fractal has less branching, for
Eb > 0. |
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