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Ann. Geophys., 24, 311-324, 2006
www.ann-geophys.net/24/311/2006/
© European Geosciences Union 2006
Field-aligned currents observed by CHAMP during the intense 2003 geomagnetic storm events
H. Wang1,2, H. Lühr2, S. Y. Ma1, J. Weygand3, R. M. Skoug4, and F. Yin1,2
1Dept. of Space Physics, College of Electronic Information, Wuhan University, P. R. China
2GeoForschungsZentrum, Potsdam, Germany
3Institute of Geophysics and Planetary Physics, University of California, Los Angeles, USA
4Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Abstract. This study concentrates on the characteristics of field-aligned
currents (FACs) in both hemispheres during the extreme storms in
October and November 2003. High-resolution CHAMP magnetic data
reflect the dynamics of FACs during these geomagnetic storms,
which are different from normal periods. The peak intensity and
most equatorward location of FACs in response to the storm phases
are examined separately for both hemispheres, as well as for the
dayside and nightside. The corresponding large-scale FAC peak
densities are, on average, enhanced by about a factor of 5 compared
to the quiet-time FACs' strengths. And the FAC densities on the
dayside are, on average, 2.5 times larger in the Southern (summer)
than in the Northern (winter) Hemisphere, while the observed
intensities on the nightside are comparable between the two
hemispheres. Solar wind dynamic pressure is correlated with the
FACs strength on the dayside. However, the latitudinal variations
of the FACs are compared with the variations in Dst and the
interplanetary magnetic field component Bz, in order to
determine how these parameters control the large-scale FACs'
configuration in the polar region. We have determined that (1) the
equatorward shift of FACs on the dayside is directly controlled by
the southward IMF Bz and there is a saturation of the
latitudinal displacement for large value of negative Bz. In the
winter hemisphere this saturation occurs at higher latitudes than
in the summer hemisphere. (2) The equatorward expansion of the
nightside FACs is delayed with respect to the solar wind input.
The poleward recovery of FACs on the nightside is slower than on
the dayside. The latitudinal variations on the nightside are
better described by the variations of the Dst index. (3) The
latitudinal width of the FAC region on the nightside spreads over
a wide range of about 25° in latitude.
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