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Ann. Geophys., 24, 339-354, 2006
www.ann-geophys.net/24/339/2006/
© European Geosciences Union 2006
Rotation of the magnetic field in Earth's magnetosheath by bulk magnetosheath plasma flow
M. Longmore1, S. J. Schwartz2, and E. A. Lucek2
1Astronomy Unit, Queen Mary, University of London, London, UK
2Blackett Laboratory, Imperial College London,London, UK
Abstract. Orientations of the observed magnetic field in Earth's dayside magnetosheath
are compared with the predicted field line-draping pattern from the Kobel and
Flückiger static magnetic field model. A rotation of the overall
magnetosheath draping pattern with respect to the model prediction is
observed. For an earthward Parker spiral, the sense of the rotation is
typically clockwise for northward IMF and anticlockwise for southward IMF.
The rotation is consistent with an interpretation which considers the
twisting of the magnetic field lines by the bulk plasma flow in the
magnetosheath. Histogram distributions describing the differences between the
observed and model magnetic field clock angles in the magnetosheath confirm
the existence and sense of the rotation. A statistically significant mean
value of the IMF rotation in the range 5°-30° is observed in
all regions of the magnetosheath, for all IMF directions, although the
associated standard deviation implies large uncertainty in the determination
of an accurate value for the rotation. We discuss the role of field-flow
coupling effects and dayside merging on field line draping in the
magnetosheath in view of the evidence presented here and that which has
previously been reported by Kaymaz et al. (1992).
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