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| Titel |
Fine-time energetic electron behavior observed by Cluster/RAPID in the magnetotail associated with X-line formation and subsequent current disruption |
| VerfasserIn |
I. I. Vogiatzis, T. A. Fritz, Q.-G. Zong, D. N. Baker, E. T. Sarris, P. W. Daly |
| 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 ; 23, no. 6 ; Nr. 23, no. 6 (2005-09-15), S.2265-2280 |
| Datensatznummer |
250015303
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| Publikation (Nr.) |
 copernicus.org/angeo-23-2265-2005.pdf |
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| Zusammenfassung |
Energetic electrons with 90deg pitch angle have been observed in the magnetotail at ~19 RE near local midnight during the recovery phase of a substorm event on 27 August 2001 (Baker et al., 2002). Based on auroral images
Baker et al. (2002) placed the substorm expansion phase between ~04:06:16 and ~04:08:19 UT. The electron enhancements perpendicular to
the ambient magnetic field occurred while the Cluster spacecraft were on closed field lines in the central plasma sheet approaching the
neutral sheet. Magnetic field and energetic particle measurements have been employed from a number of satellites, in order to determine the
source and the subsequent appearance of these electrons at the Cluster location. It is found that ~7.5 min after an X-line formation
observed by Cluster (Baker et al., 2002) a current disruption event took place inside geosynchronous orbit and subsequently expanded both in
local time and tailward, giving rise to field-aligned currents and the formation of a current wedge. A synthesis of tail reconnection and
the cross-tail current disruption scenario is proposed for the substorm global initiation process: When a fast flow with northward magnetic
field, produced by magnetic reconnection in the midtail, abruptly decelerates at the inner edge of the plasma sheet, it compresses the plasma
populations earthward of the front, altering dynamically the Bz magnetic component in the current sheet. This provides the necessary and
sufficient conditions for the kinetic cross-field streaming/current (KCSI/CFCI) instability (Lui et al., 1990, 1991) to initiate. As soon as
the ionospheric conductance increases over a threshold level, the auroral electrojet is greatly intensified (see Fig. 2 in Baker et al., 2002), which leads to the formation of the substorm current wedge and dipolarization of the magnetic field. This substorm scenario
combines the near-Earth neutral line and the current disruption for the initiation of substorms, at least during steady southward IMF.
One can conclude the following: The observations suggest that the anisotropic electron increases observed by Cluster are not related to an acceleration
mechanism associated with the X-line formation in the midtail, but rather these particles are generated in the dusk magnetospheric sector
due to the longitudinal and tailward expansion of a current disruption region and subsequently observed at the Cluster location with no
apparent energy dispersion.
Keywords. Magnetospheric physics (Magnetotail; Plasma
convection; Storms and substorms) |
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