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| Titel |
High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements |
| VerfasserIn |
M. Forster, S. E. Haaland, G. Paschmann, J. M. Quinn, R. B. Torbert, H. Vaith, 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 ; 26, no. 9 ; Nr. 26, no. 9 (2008-09-12), S.2685-2700 |
| Datensatznummer |
250016219
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| Publikation (Nr.) |
 copernicus.org/angeo-26-2685-2008.pdf |
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| Zusammenfassung |
| In this study, we investigate statistical, systematic variations of the
high-latitude convection cell structure during northward IMF.
Using 1-min-averages of Cluster/EDI electron drift observations above
the Northern and Southern polar cap areas for six and a half years
(February 2001 till July 2007), and mapping the spatially distributed
measurements to a common reference plane at ionospheric level in a
magnetic latitude/MLT grid, we obtained regular drift patterns
according to the various IMF conditions.
We focus on the particular conditions during northward IMF, where
lobe cells at magnetic latitudes >80°
with opposite (sunward) convection over the central polar cap are
a permanent feature in addition to the main convection cells
at lower latitudes. They are due to reconnection processes at the
magnetopause boundary poleward of the cusp regions.
Mapped EDI data have a particular good coverage within the central part
of the polar cap, so that these patterns and their dependence on various
solar wind conditions are well verified in a statistical sense.
On average, 4-cell convection pattern are shown as regular structures
during periods of nearly northward IMF with the tendency of a
small shift toward negative clock angles.
The positions of these high-latitude convection foci are within 79°
to 85° magnetic latitude and 09:00–15:00 MLT. The MLT positions are
approximately symmetric ±2 h about 11:30 MLT, i.e. slightly
offset from midday toward prenoon hours,
while the maximum (minimum) potential of the high-latitude cells
is at higher magnetic latitudes near their maximum potential difference
at ≈−10° to −15° clock angle for the North (South)
Hemisphere.
With increasing clock angle distances from ≈IMFBz+,
a gradual transition occurs from the 4-cell pattern via a 3-cell
to the common 2-cell convection pattern, in the course of which
one of the medium-scale high-latitude dayside cells diminishes and disappears
while the other intensifies and merges with the opposite main cell of the
same polarity to form the large "round-shaped" convection cell when
approaching a well-known IMFBy-dominated configuration.
Opposite scenarios with interchanged roles of the respective cells occur
for the opposite turning of the clock angle and at the Southern Hemisphere.
The high-latitude dayside cells become more pronounced with increasing
magnitude of the IMF vector. |
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