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| Titel |
CLUSTER encounters with the high altitude cusp: boundary structure and magnetic field depletions |
| VerfasserIn |
P. J. Cargill, M. W. Dunlop, B. Lavraud, R. C. Elphic, D. L. Holland, K. Nykyri, A. Balogh, I. Dandouras, H. Rème |
| 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. 5 ; Nr. 22, no. 5 (2004-04-08), S.1739-1754 |
| Datensatznummer |
250014873
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| Publikation (Nr.) |
 copernicus.org/angeo-22-1739-2004.pdf |
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| Zusammenfassung |
Data from the four spacecraft Cluster mission during a high altitude cusp
crossing on 13 February 2001 are presented. The spacecraft configuration
has one leading spacecraft, with the three trailing spacecraft lying in a plane that
corresponds roughly to the nominal magnetopause surface. The typical
spacecraft separation is approximately 600km. The encounter occurs under
conditions of strong and steady southward Interplanetary Magnetic Field
(IMF). The cusp is identified as a seven-minute long depression in the
magnetic field, associated with ion heating and a high abundance of
He+. Cusp entry involves passage through a magnetopause boundary that
has undergone very significant distortion from its nominal shape, is moving
rapidly, and exhibits structure on scales of the order of the spacecraft separation
or less. This boundary is associated with a rotation of the magnetic field,
a normal field component, and a plasma flow into the cusp of approximately
35 km/s. However, it cannot be identified positively as a rotational
discontinuity. Exit from the cusp into the lobe is through a boundary that
is initially sharp, but then retreats tailward at a few km/s. As the leading
spacecraft passes through this boundary, there is a plasma flow out of the
cusp of approximately 30km/s, suggesting that this is not a tangential
discontinuity. A few minutes after exit from the cusp, the three trailing
the spacecraft see a single cusp-like signature in the magnetic field. There is
an associated temperature increase at two of the three trailing spacecraft. Timing
measurements indicate that this is due to cusp-like regions detaching from
the rear of the cusp boundary, and moving tailward. The magnetic field in
the cusp is highly disordered, with no obvious relation between the four
spacecraft, indicative of structure on scales <<600km. However, the
plasma moments show only a gradual change over many minutes. A similar cusp
crossing on 20 February 2001 also shows a field depression and highly
dynamic boundaries.
Key words. Magnetospheric physics (magnetopause, cusp
and boundary layers; solar wind-magnetosphere interactions)
– Space plasma physics (discontinuities) |
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