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Ann. Geophys., 26, 1581-1595, 2008
www.ann-geophys.net/26/1581/2008/
© European Geosciences Union 2008
IMF dependence of high-latitude thermospheric wind pattern derived from CHAMP cross-track measurements
M. Förster1, S. Rentz1, W. Köhler1, H. Liu2, and S. E. Haaland3,4
1GeoForschungsZentrum (GFZ) Potsdam, Potsdam, Germany
2Hokkaido University, Div. of Earth and Planet. Science, Sapporo, Japan
3Max-Planck Institute für extraterrestrische Physik (MPE), Garching, Germany
4Department of Physics, University of Bergen, Norway
Abstract. Neutral thermospheric wind pattern at high latitudes obtained
from cross-track acceleration measurements of the CHAMP satellite
above both North and South polar regions are statistically
analyzed in their dependence on the Interplanetary Magnetic
Field (IMF) direction in the GSM y-z plane (clock angle).
We compare this dependency with magnetospheric convection pattern
obtained from the Cluster EDI plasma drift measurements under the
same sorting conditions.
The IMF-dependency shows some similarity with the corresponding
high-latitude plasma convection insofar that the larger-scale
convection cells, in particular the round-shaped dusk cell for
ByIMF+ (ByIMF−) conditions at the Northern (Southern)
Hemisphere, leave their marks on the dominant general transpolar
wind circulation from the dayside to the nightside.
The direction of the transpolar circulation is generally
deflected toward a duskward flow, in particular in the evening
to nighttime sector.
The degree of deflection correlates with the IMF clock angle.
It is larger for ByIMF+ than for ByIMF− and is systematically
larger (~5°) and appear less structured at the Southern
Hemisphere compared with the Northern.
Thermospheric cross-polar wind amplitudes are largest for
BzIMF−/ByIMF− conditions
at the Northern Hemisphere, but for BzIMF−/ByIMF+
conditions at the Southern because the magnetospheric convection
is in favour of largest wind accelerations over the polar cap
under these conditions.
The overall variance of the thermospheric wind magnitude at
Southern high latitudes is larger than for the Northern.
This is probably due to a larger "stirring effect" at the
Southern Hemisphere because of the larger distance
between the geographic and geomagnetic frameworks.
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