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| Titel |
Initiation of ballooning instability in the near-Earth plasma sheet prior to the 23 March 2007 THEMIS substorm expansion onset |
| VerfasserIn |
P. Zhu, J. Raeder, K. Germaschewski, C. C. Hegna |
| 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. 3 ; Nr. 27, no. 3 (2009-03-06), S.1129-1138 |
| Datensatznummer |
250016445
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| Publikation (Nr.) |
 copernicus.org/angeo-27-1129-2009.pdf |
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| Zusammenfassung |
| In this work, we analyze the ballooning stability of the near-Earth
plasma sheet prior to the initial expansion onset of the 23 March
2007 THEMIS substorm event. Using solar wind data from WIND satellite
observation for the substorm event as an input at dayside, we
reconstructed a sequence of global magnetospheric configurations
around the expansion onset by means of OpenGGCM simulation. These
simulations have reproduced most of the salient features, including
the onset timing, observed in the THEMIS substorm
event (Raeder et al., 2008). The ballooning instability criterion is
evaluated using eigenvalue analyses for the near-Earth plasma sheet
region when the configuration attains a quasi-static equilibrium
condition prior to the onset. Our analysis of the evolution of the
near-Earth magnetotail region during the substorm growth phase (10:10 UT
to 10:43 UT) reveals a correlation between the breaching of the
ballooning stability condition and the initial expansion onset in the
temporal domain. The analysis indicates that the ballooning
instability is at first initiated by the stretching of closed field
lines near the region with a local nonzero minimum in normal component
of magnetic field (Bz>0) associated with the formation of a
bipolar-flow pattern in the near-Earth plasma sheet around
10 RE. The subsequent initiation of ballooning instability with
enhanced growth rate occurs (about 28 min later) on those most
stretched closed field lines Earthward of the neutral line following
the formation and the tailward recession of a plasmoid. |
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