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Ann. Geophys., 24, 2201-2208, 2006
www.ann-geophys.net/24/2201/2006/
© European Geosciences Union 2006
Reconfiguration of polar-cap plasma in the magnetic midnight sector
S. E. Pryse1, A. G. Wood1, H. R. Middleton1, I. W. McCrea2, and M. Lester3
1Institute of Mathematical and Physical Sciences, University of Wales Aberystwyth, UK
2Space Physics Division, Space Science and Technology Department, CCLRC Rutherford Appleton Laboratory, UK
3Department of Physics, University of Leicester, UK
Abstract. Radio tomography and the EISCAT and SuperDARN radars have been used to
identify long-lived, high-altitude, cold plasma in the antisunward
convective flow across the polar cap. The projection of the feature to later
times suggests that it was reconfigured in the Harang discontinuity to form
an enhancement that was elongated in longitude in the sunward return flow of
the high-latitude convection pattern. Comparison with a tomographic image at
a later time supports the interpretation of a polar patch being reconfigured
into a boundary blob. There is also evidence for a second plasma enhancement
equatorward of the reconfigured blob, likely to have been produced by in
situ precipitation. The observations indicate that the two mechanisms
proposed in the literature for the production of boundary blobs are
operating simultaneously to form two distinct density features separated
slightly in latitude.
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