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| Titel |
High-latitude plasma convection from Cluster EDI measurements: method and IMF-dependence |
| VerfasserIn |
S. E. Haaland, G. Paschmann, M. Forster, J. M. Quinn, R. B. Torbert, C. E. McIlwain, H. Vaith, P. A. Puhl-Quinn, C. A. Kletzing |
| 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 ; 25, no. 1 ; Nr. 25, no. 1 (2007-02-01), S.239-253 |
| Datensatznummer |
250015774
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| Publikation (Nr.) |
 copernicus.org/angeo-25-239-2007.pdf |
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| Zusammenfassung |
| We have used vector measurements of the electron drift velocity made by the Electron Drift Instrument (EDI) on
Cluster between February 2001 and March 2006 to derive statistical maps of the high-latitude plasma
convection. The EDI measurements,
obtained at geocentric distances between ~4 and ~20 RE over both hemispheres, are mapped
into the polar ionosphere, and sorted according to the clock-angle of the interplanetary magnetic field (IMF),
measured at ACE and propagated to Earth, using best estimates of the orientation of the IMF variations.
Only intervals of stable IMF are used, based on the magnitude of a "bias-vector" constructed from
30-min averages. The resulting data set consists of a total of 5862 h of EDI data. Contour maps of
the electric potential in the polar ionosphere are subsequently derived from the mapped and averaged
ionospheric drift vectors. Comparison with published statistical results based on Super Dual Auroral Radar Network
(SuperDARN) radar and low-altitude satellite measurements shows excellent agreement between the average convection patterns,
and in particular the lack of mirror-symmetry between the effects of positive and negative IMF By,
the appearance of a duskward flow component for strongly southward IMF, and the general weakening of the
average flows and potentials for northerly IMF directions. This agreement lends credence to the validity of the
assumption underlying the mapping of the EDI data, namely that magnetic field lines are equipotentials.
For strongly northward IMF the mapped EDI data show the clear emergence of two counter-rotating lobe cells
with a channel of sunward flow between them. The total potential drops across the polar caps obtained from
the mapped EDI data are intermediate between the radar and the low-altitude satellite results. |
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