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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 8
Ann. Geophys., 26, 2203-2216, 2008
https://doi.org/10.5194/angeo-26-2203-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: 13th International EISCAT Workshop

Ann. Geophys., 26, 2203-2216, 2008
https://doi.org/10.5194/angeo-26-2203-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  05 Aug 2008

05 Aug 2008

Multi-instrument observations of nightside plasma patches under conditions of IMF Bz positive

A. G. Wood1, S. E. Pryse1, H. R. Middleton1, and V. S. C. Howells2 A. G. Wood et al.
  • 1Aberystwyth University, Aberystwyth, UK
  • 2Rutherford Appleton Laboratory, Didcot, UK

Abstract. Results are presented from two multi-instrument case studies showing patches of cold, long-lived plasma in the winter nightside ionosphere during times when the z-component of the Interplanetary Magnetic Field (IMF Bz) was positive. These enhancements were coincident with the antisunward convective plasma drift, flowing from polar to nightside auroral latitudes. In the first case, on 5 December 2005 with IMF By negative, two regions of enhanced electron density were observed extended in MLT in the magnetic midnight sector separated by lower densities near midnight. It is likely that the earlier enhancement originated on the dayside near magnetic noon and was transported to the nightside sector in the convective flow, whilst the later feature originated in the morning magnetic sector. The lower densities separating the two enhancements were a consequence of a pair of lobe cells essentially blocking the direct antisunward cross polar flow from the dayside. A second case study on 4 February 2006 with IMF By positive revealed a single nightside enhancement likely to have originated in the morning magnetic sector. These multi-instrument investigations, incorporating observations by the EISCAT radar facility, the SuperDARN network and radio tomography, reveal that plasma flowing from the dayside can play a significant role in the nightside ionosphere under conditions of IMF Bz positive. The observations are reinforced by simulations of flux-tube transport and plasma decay.

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