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| Titel |
Shape, size, velocity and field-aligned currents of dayside plasma injections: a multi-altitude study |
| VerfasserIn |
A. Marchaudon, J.-C. Cerisier, M. W. Dunlop, F. Pitout, J.-M. Bosqued, A. N. Fazakerley |
| 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 (2009-03-12), S.1251-1266 |
| Datensatznummer |
250016453
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| Publikation (Nr.) |
 copernicus.org/angeo-27-1251-2009.pdf |
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| Zusammenfassung |
| On 20 February 2005, Cluster in the outer magnetosphere and Double Star-2
(TC-2) at mid-altitude are situated in the vicinity of the northern
cusp/mantle, with Cluster moving sunward and TC-2 anti-sunward. Their
magnetic footprints come very close together at about 15:28 UT, over the
common field-of-view of SuperDARN radars. Thanks to this conjunction, we
determine the velocity, the transverse sizes, perpendicular and parallel to
this velocity, and the shape of three magnetic flux tubes of magnetosheath
plasma injection. The velocity of the structures determined from the Cluster
four-spacecraft timing analysis is almost purely antisunward, in contrast
with the antisunward and duskward convection velocity inside the flux tubes.
The transverse sizes are defined from the Cluster-TC-2 separation
perpendicular to the magnetic field, and from the time spent by a Cluster
spacecraft in one structure; they are comprised between 0.6 and 2 RE in
agreement with previous studies. Finally, using a comparison between the
eigenvectors deduced from a variance analysis of the magnetic perturbation
at the four Cluster and at TC-2, we show that the upstream side of the
injection flux tubes is magnetically well defined, with even a concave front
for the third one giving a bean-like shape, whereas the downstream side is
far more turbulent. We also realise the first quantitative comparison
between field-aligned currents at Cluster calculated with the curlometer
technique and with the single-spacecraft method, assuming infinite parallel
current sheets and taking into account the velocity of the injection flux
tubes. The results agree nicely, confirming the validity of both methods.
Finally, we compare the field-aligned current distribution of the three
injection flux tubes at the altitudes of Cluster and TC-2. Both profiles are
fairly similar, with mainly a pair of opposite field-aligned currents,
upward at low-latitude and downward at high-latitude. In terms of intensity,
the field-aligned currents at Cluster are two to three times less intense
than at TC-2 for the first two flux tubes, in agreement with magnetic field
line convergence. For the third flux tube, the intensity is equal, which is
explained by the fact that TC-2 crosses the tube on its edge. Finally, the
analysis of the ion and electron moments at Cluster shows that the
field-aligned currents result from a small difference between upward ion and
electron fluxes. |
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