Articles | Volume 22, issue 7
Ann. Geophys., 22, 2577–2585, 2004

Special issue: Spatio-temporal analysis and multipoint measurements in space...

Ann. Geophys., 22, 2577–2585, 2004

  14 Jul 2004

14 Jul 2004

Density structures inside the plasmasphere: Cluster observations

F. Darrouzet1, P. M. E. Décréau2, J. De Keyser1, A. Masson3, D. L. Gallagher4, O. Santolik5,*, B. R. Sandel6, J. G. Trotignon2, J. L. Rauch2, E. Le Guirriec2, P. Canu7, F. Sedgemore8, M. André9, and J. F. Lemaire1 F. Darrouzet et al.
  • 1Belgian Institute for Space Aeronomy (IASB-BIRA), 1180 Brussels, Belgium
  • 2Laboratoire de Physique et Chimie de l’Environnement (LPCE/CNRS), Université d’Orléans, 45071 Orléans, France
  • 3Research and Scientific Support Department (RSSD), ESTEC-ESA, 2201-AG Noordwijk, The Netherlands
  • 4Marshall Space Flight Center (MSFC), NASA, Huntsville, AL 35805, USA
  • 5Faculty of Mathematics and Physics (MFF), Charles University, 121 16 Prague, Czech Republic
  • 6Lunar and Planetary Laboratory (LPL), University of Arizona, Tucson, AZ 85721, USA
  • 7Centre d’étude des Environnements Terrestre et Planétaires (CETP/CNRS), Université de Versailles Saint-Quentin-en-Yvelines, 78140 Vélizy, France
  • 8Formerly at Danish Space Research Institute (DSRI), 2100 Copenhagen, Denmark
  • 9Swedish Institute of Space Physics (IRFU), Uppsala division, 751 21 Uppsala, Sweden
  • *also at Institute of Atmospheric Physics (IAP/CAS), 141 31 Prague, Czech Republic

Abstract. The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on 11 April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity of the boundaries of the plume and of the irregularities from the time delays between those boundaries in the four individual density profiles, assuming they are planar. These new observations yield novel insights about the occurrence of density irregularities, their geometry and their dynamics. These in-situ measurements are compared with global images of the plasmasphere from the EUV imager on board the IMAGE satellite.