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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 12
Ann. Geophys., 24, 3391–3401, 2006
https://doi.org/10.5194/angeo-24-3391-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 3391–3401, 2006
https://doi.org/10.5194/angeo-24-3391-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  21 Dec 2006

21 Dec 2006

On the structure of field-aligned currents in the mid-altitude cusp

A. Marchaudon1,2, J.-C. Cerisier3, J.-M. Bosqued4, C. J. Owen1, A. N. Fazakerley1, and A. D. Lahiff1 A. Marchaudon et al.
  • 1Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH5 6NT, Surrey, UK
  • 2Now at: Laboratoire de Physique et Chimie de l'Environnement, 3A avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
  • 3Université Pierre et Marie Curie-Paris6; Centre d'Etude des Environnements Terrestre et Planétaires, 4 avenue de Neptune, 94107 Saint-Maur-des-Fossés Cedex, France
  • 4Centre d'Etude Spatiale des Rayonnements, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 4, France

Abstract. We analyse two crossings of the polar cusp at mid-altitudes (≈4 RE) by Cluster in order to study the structure of field-aligned currents associated with the injection of magnetosheath plasma. The current density is deduced independently from magnetic field and from particle flux measurements. In both cases the data are carefully tested. Magnetic fluctuations are analysed by discriminating between those compatible with the plane current sheet hypothesis under which the current density can be calculated safely, and those resulting from filamentary current structures. At medium transverse scales (80 km), the structure of the currents is more often tube-like than sheet-like, and current sheets are not systematically elongated in the east-west direction. The total particle current is calculated from the electron and ion measurements. For electrons, the full energy range is taken into account, from above the photoelectron threshold up to 32 keV. Magnetosheath plasma injections are well correlated with pairs of field-aligned currents. In both cases, the parallel current is mainly carried by electrons while ions contribute for about 20%. In the plane current sheets, the ratio between magnetic and particle currents shows large variations between 0.4 and 1.1. These fluctuations can be explained by the convective motion of the current sheets.

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