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| Titel |
Two satellite study of substorm expansion near geosynchronous orbit |
| VerfasserIn |
Ø. Holter, P. Galopeau, A. Roux, S. Perraut, A. Pedersen, A. Korth, T. Bösinger |
| 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 ; 22, no. 12 ; Nr. 22, no. 12 (2004-12-22), S.4299-4310 |
| Datensatznummer |
250015092
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| Publikation (Nr.) |
 copernicus.org/angeo-22-4299-2004.pdf |
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| Zusammenfassung |
During several time intervals in 1979–1980 the satellites
GEOS-2 and SCATHA were situated relatively close on the nightside of the
Earth at geosynchronous distances.
Several substorm events were identified during these periods.
The event considered in this paper was recorded on 22 May 1979, when the satellites
were separated by less than 30min in local time around 21:00 LT.
The observed 45 to 60 s delay of magnetic signatures observed at
the two s/c indicates
a westward expansion of ~7.7°/min.
At the two s/c, the magnetic signatures are,
in particular for the azimuthal magnetic field components,
quite different.
At GEOS-2, being close to the magnetic equator, the dominant feature is
a dipolarization with a weak field-aligned current signature corresponding
to
a symmetric current which cancels at the equator.
On SCATHA, however, being close to the current sheet boundary,
the azimuthal magnetic field indicates a strong field-aligned
Birkeland current structure.
On both s/c the first indication of an approaching substorm was an increase
in
the high energy ion flux followed by a
reduction in the flux intensity of energetic electrons and a further
tailward stretching of the magnetic field, starting ~2min
before the onset of the magnetic field dipolarization.
The tailward stretching, the observed variations of the magnetic field
components, and the subsequent dipolarization are interpreted in terms
of an azimuthally tilted field-aligned current system passing
the s/c on the tailward side from east to west. The westward expansion and dipolarization observed
at the two s/c are consistent
with the propagation of a Rayleigh-Taylor type instability.
The increased radial ion flux corresponds to the ExB-drift due to the
substorm associated electric field.
Key words. Magnetospheric physics (storms and substorms;
plasma waves and instabilities; current systems) |
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