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| Titel |
THEMIS ground-space observations during the development of auroral spirals |
| VerfasserIn |
A. Keiling, V. Angelopoulos, J. M. Weygand, O. Amm, E. Spanswick, E. Donovan, S. Mende, J. McFadden, D. Larson, K.-H. Glassmeier, H. U. Auster |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 11 ; Nr. 27, no. 11 (2009-11-27), S.4317-4332 |
| Datensatznummer |
250016713
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| Publikation (Nr.) |
 copernicus.org/angeo-27-4317-2009.pdf |
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| Zusammenfassung |
| A simultaneous observation of an auroral spiral and its generator region in
the near-Earth plasma sheet is rather unlikely. Here we present such observations
using the THEMIS spacecraft as well as the THEMIS ground
network of all-sky imagers and magnetometers. Two consecutive auroral
spirals separated by approximately 14 min occurred during a substorm on 19
February 2008. The spirals formed during the expansion phase and a
subsequent intensification, and were among the brightest features in the
aurora with diameters of 200–300 km. The duration for the formation and
decay of each spiral was less than 60 s. Both spirals occurred shortly after
the formation of two oppositely rotating plasma flow vortices in space,
which were also accompanied by dipolarizations and ion injections, at ~11 RE
geocentric distance. Observations and model calculations
also give evidence for a magnetic-field-aligned current generation of approximately 0.1 MA via the
flow vortices, connecting the generator region of the spirals with the
ionosphere, during the formation of both spirals. In the ionosphere, a pair
of equivalent ionospheric current (EIC) vortices with opposite rotations
(corresponding to upward and downward currents) was present during
both auroral spirals with enhanced EICs and ionospheric flows at the
locations of the auroral spirals and along the auroral arcs. The combined
ground and space observations suggest that each auroral
spiral was powered by two oppositely rotating plasma flow vortices that caused a current enhancement in the substorm
current wedge. |
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