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| Titel |
The distribution of the ring current: Cluster observations |
| VerfasserIn |
Q.-H. Zhang, M. W. Dunlop, M. Lockwood, R. Holme, Y. Kamide, W. Baumjohann, R.-Y. Liu, H.-G. Yang, E. E. Woodfield, H.-Q. Hu, B.-C. Zhang, S.-L. Liu |
| 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. 9 ; Nr. 29, no. 9 (2011-09-28), S.1655-1662 |
| Datensatznummer |
250017095
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| Publikation (Nr.) |
 copernicus.org/angeo-29-1655-2011.pdf |
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| Zusammenfassung |
| Extending previous studies, a full-circle investigation of the ring current
has been made using Cluster 4-spacecraft observations near perigee, at times
when the Cluster array had relatively small separations and nearly regular
tetrahedral configurations, and when the Dst index was greater than −30 nT
(non-storm conditions). These observations result in direct estimations of
the near equatorial current density at all magnetic local times (MLT) for
the first time and with sufficient accuracy, for the following observations.
The results confirm that the ring current flows westward and show that the
in situ average measured current density (sampled in the radial range accessed by
Cluster ~4–4.5 RE) is asymmetric in MLT, ranging from 9 to 27 nA m−2. The direction of current is shown to be very well ordered for
the whole range of MLT. Both of these results are in line with previous
studies on partial ring extent. The magnitude of the current density,
however, reveals a distinct asymmetry: growing from 10 to 27 nA m−2 as
azimuth reduces from about 12:00 MLT to 03:00 and falling from 20 to 10 nA m−2
less steadily as azimuth reduces from 24:00 to 12:00 MLT. This result has not been
reported before and we suggest it could reflect a number of effects.
Firstly, we argue it is consistent with the operation of region-2 field
aligned-currents (FACs), which are expected to flow upward into the ring
current around 09:00 MLT and downward out of the ring current around 14:00 MLT.
Secondly, we note that it is also consistent with a possible asymmetry in
the radial distribution profile of current density (resulting in higher peak
at ~4–4.5 RE). We note that part of the enhanced current could
reflect an increase in the mean AE activity (during the periods in which
Cluster samples those MLT). |
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