Articles | Volume 22, issue 7
Ann. Geophys., 22, 2473–2483, 2004

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

Ann. Geophys., 22, 2473–2483, 2004

  14 Jul 2004

14 Jul 2004

Shell-like configuration in O+ ion velocity distribution at high altitudes in the dayside magnetosphere observed by Cluster/CIS

S. Joko1, H. Nilsson1, R. Lundin1, B. Popielawska2, H. Rème3, M. B. Bavassano-Cattaneo4, G. Paschmann5, A. Korth6, L. M. Kistler7, and G. K. Parks8 S. Joko et al.
  • 1Swedish Institute of Space Physics (IRF), P.O. Box 812 SE-98128 Kiruna, Sweden
  • 2Space Research Center (P.A.S.), Warsaw, Poland
  • 3Centre d’Etude Spatiale des Rayonnements, Toulouse, France
  • 4Instituto di Fisica dello Spazio Interplanetario, Roma, Italy
  • 5Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany
  • 6Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany
  • 7University of New Hampshire, Durham, USA
  • 8Space Science Laboratory, UC Berkeley, USA

Abstract. We report shell-like configurations seen in O+ ion velocity distributions. One case was observed above 8RE in radial distance in the dayside magnetosphere, presumably in the mantle region, during the observation period of 09:30-10:00 UT on 12 April 2001 by the CIS instrument on board the Cluster satellite. This shell-like configuration was different from so-called "conics" or "beams": the lower energy (cold) population and the higher energy partial shell part were seen together, but there was no obvious signature of heating process. With respect to H+ ion velocity distributions observed simultaneously, transverse heating (so-called in "pan-cake" shape) or field-aligned energisation configurations were seen as the result of heating/energisation processes and the upward-going part of the distribution also formed a half spherical thick shell configuration. Concerning O+ ion heating in the case of 12 April 2001, it was obviously observed when the spacecraft passed through the mantle region close to the poleward cusp. As the spacecraft moved toward the dayside cusp shell-like (or dome shape) velocity distributions appeared apparently and continued to be observed until the spacecraft reached the magnetopause according to two other different cases (13 February 2001 and 14 April 2001). Two other cases were observed in the Southern Hemisphere and the spacecraft was supposed to pass through the dayside cusp toward the mantle region at higher altitudes (9-11RE). O+ ion velocity distributions in these cases show pre-/post-structured shell-like configurations, depending on the observation sites (mantle or dayside cusp).