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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 3
Ann. Geophys., 26, 583–591, 2008
https://doi.org/10.5194/angeo-26-583-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 26, 583–591, 2008
https://doi.org/10.5194/angeo-26-583-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  26 Mar 2008

26 Mar 2008

Magnetosphere-ionosphere coupling during periods of extended high auroral activity: a case study

S. Liléo1, G. T. Marklund1, T. Karlsson1, T. Johansson1,*, P.-A. Lindqvist1, A. Marchaudon2, A. Fazakerley3, C. Mouikis4, and L. M. Kistler4 S. Liléo et al.
  • 1Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden
  • 2LPCE, CNRS-Université d'Orléans, Orléans, France
  • 3Mullard Space Science Laboratory, University College London, UK
  • 4Space Science Center, University of New Hampshire, Durham, USA
  • *now at: Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA

Abstract. Results are presented from a case study of a plasma boundary crossing by the Cluster spacecraft during an extended period of high auroral activity. The boundary between the magnetotail lobe region of the Southern Hemisphere and the plasma sheet boundary layer, was characterized by intense electric and magnetic field variations, structured upward accelerated ion beams, narrow-scale large field-aligned Poynting fluxes directed upward away from the ionosphere, and a relatively sharp plasma density gradient.

The observations are shown to be consistent with the concept of a multi-layered boundary with temporal and/or spatial variations in the different layers. H+ and O+ ion beams are seen to be accelerated upwards both by means of a field-aligned electric field and by magnetic pumping caused by large-amplitude and low-frequency electric field fluctuations. The peak energy of the ion beams may here be used as a diagnostic tool for the temporal evolution of the spatial structures, since the temporal changes occur on a time-scale shorter than the times-of-flight of the detected ion species.

The case study also shows the boundary region to be mainly characterized by a coupling of the detected potential structures to the low ionosphere during the extended period of high auroral activity, as indicated by the intense field-aligned Poynting fluxes directed upward away from the ionosphere.

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