|
|
 |
|
|
Ann. Geophys., 22, 2473-2483, 2004
www.ann-geophys.net/22/2473/2004/
© European Geosciences Union 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
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).
Full Article in PDF (1676 KB) |
|
|
