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| Titel |
Timing mirror structures observed by Cluster with a magnetosheath flow model |
| VerfasserIn |
V. Génot, L. Broussillou, E. Budnik, P. Hellinger, P. M. Trávníček, E. Lucek, I. Dandouras |
| 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. 10 ; Nr. 29, no. 10 (2011-10-24), S.1849-1860 |
| Datensatznummer |
250017110
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| Publikation (Nr.) |
 copernicus.org/angeo-29-1849-2011.pdf |
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| Zusammenfassung |
| The evolution of structures associated with mirror modes during their flow in
the Earth's magnetosheath is studied. The fact that the related magnetic
fluctuations can take distinct shapes, from deep holes to high peaks, has
been assessed in previous works on the observational, modeling and numerical
points of view. In this paper we present an analytical model for the flow
lines and velocity magnitude inside the magnetosheath. This model is used to
interpret almost 10 years of Cluster observations of mirror structures: by
back tracking each isolated observation to the shock, the "age", or flow
time, of these structures is determined together with the geometry of the
shock. Using this flow time the evolutionary path of the structures may be
studied with respect to different quantities: the distance to mirror
threshold, the amplitude of mirror fluctuations and the skewness of the
magnetic amplitude distribution as a marker of the shape of the structures.
These behaviours are confronted to numerical simulations which confirm the
dynamical perspective gained from the association of the statistical analysis
and the analytical model: magnetic peaks are mostly formed just behind the
shock and are quickly overwhelmed by magnetic holes as the plasma conditions
get more mirror stable. The amplitude of the fluctuations are found to
saturate before the skewness vanishes, i.e. when both structures
quantitatively balance each other, which typically occurs after a flow time
of 100–200 s in the Earth's magnetosheath. Comparison with other astrophysical
contexts is discussed. |
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