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| Titel |
Brightening of onset arc precedes the dipolarization onset: THEMIS observations of two events on 1 March 2008 |
| VerfasserIn |
J. R. Kan, H. Li, C. Wang, H. U. Frey, M. V. Kubyshkina, A. Runov, C. J. Xiao, L. H. Lyu, W. Sun |
| 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 ; 29, no. 11 ; Nr. 29, no. 11 (2011-11-17), S.2045-2059 |
| Datensatznummer |
250017126
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| Publikation (Nr.) |
 copernicus.org/angeo-29-2045-2011.pdf |
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| Zusammenfassung |
| We present a new M-I coupling model of substorm during
southward IMF based on the THEMIS observations of two events on 1 March
2008. The first event (E-1) was classified as a pseudo-breakup: brightening
of the onset arc preceded the first dipolarization onset by ∼71 ± 3 s,
but the breakup arcs faded within ∼5 min without substantial
poleward expansion and the dipolarization stopped and reversed to thinning.
The second event (E-2) was identified as a substorm: brightening of the
second onset arc preceded the second dipolarization onset by ∼80 ± 3 s,
leading to a full-scale expanding auroral bulge during the substorm
expansion phase for ∼20 min. The Alfvén travel time from the
ionosphere to the dipolarization onset region is estimated at ∼69.3 s
in E-1; at ∼80.3 s in E-2, which matched well with the observed
time delay of the dipolarization onset after the brightening of the onset
arc, respectively in E-1 and E-2. Brightening of the onset arc precedes the
dipolarization onset suggest that the onset arc brightening is caused by the
intense upward field-aligned currents originating from the divergence of the
Cowling electrojet in the ionosphere. The Cowling electrojet current loop
(CECL) is formed to close the field-aligned currents at all times. The
closure current in the Alfvén wavefront is anti-parallel to the
cross-tail current. Dipolarization onset occurs when the Alfvén
wavefront incident on the near-Earth plasma sheet to disrupt the cross-tail
current in the dipolarization region. Slow MHD waves dominate the disruption
of the cross-tail current in the dipolarization region. |
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