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Ann. Geophys., 26, 583-591, 2008
www.ann-geophys.net/26/583/2008/
© European Geosciences Union 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
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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