HR: 0800h
AN: SM41C-1199    [Abstracts]
TI: Acceleration and Precipitation of Energetic Ionospheric Ion Beams in the Auroral Region: Cluster Observations and Large Scale Modeling
AU: * Bosqued, J M
EM: bosqued@cesr.fr
AF: Centre Etude Spatiale des Rayonnements, CESR/CNRS, 9 Av. Colonel Roche BP 4346, Toulouse, 31028 France
AU: Ashour-Abdalla, M
SM41C-1199 AF: Institute of Geophysics and Planetary Physics, UCLA, 405 Hilgard Avenue, Los Angeles, CA 90095-1567 United States
AU: Ashour-Abdalla, M
SM41C-1199 AF: Department of Physics, UCLA, 405 Hilgard Avenue, Los Angeles, CA 90095-1547 United States
AU: Umeda, T
SM41C-1199 AF: Institute of Geophysics and Planetary Physics, UCLA, 405 Hilgard Avenue, Los Angeles, CA 90095-1567 United States
AU: El Alaoui, M
SM41C-1199 AF: Institute of Geophysics and Planetary Physics, UCLA, 405 Hilgard Avenue, Los Angeles, CA 90095-1567 United States
AU: Peroomian, V
SM41C-1199 AF: Institute of Geophysics and Planetary Physics, UCLA, 405 Hilgard Avenue, Los Angeles, CA 90095-1567 United States
AU: Marchaudon, A
SM41C-1199 AF: Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT United Kingdom
AU: Dunlop, M W
SM41C-1199 AF: Space Physics Division, SST Department, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX United Kingdom
AU: Paschmann, G
SM41C-1199 AF: Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstrasse, Garching, 85748 Germany
AB: The Cluster spacecraft offer a unique opportunity to investigate the origin of dispersed ion beams observed at mid-latitudes (4-5 RE) in the nightside auroral region. In this paper we present a detailed study of one event observed during the recovery phase of a magnetospheric substorm. In contrast to the suggestion that energetic ions sporadically originate in the distant PSBL, we argue that energetic (5-15 keV), field-aligned H+ ions observed by Cluster are ejected at the top of a steady and localized auroral acceleration region. These ions bounce on closed field-lines and are dispersed in latitude by the E x B magnetospheric filter. Echoes of energetic ionospheric H+ ions are observed by each of the Cluster spacecraft as they pass through the high latitude poleward edge of the plasmasheet. Such multiple-spacecraft measurements are well-suited to test our ability to model very complex magnetospheric situations. Detailed time-dependent modeling of this event will be presented. In order to correctly interpret the observed spatial dispersion, global MHD simulations demonstrate that vortices or channels of tailward convection are locally generated in the neutral sheet at 14-18 RE distance in the post-midnight sector, i.e., on field lines connected with the mid-altitude region crossed by Cluster. By using the Large Scale Kinetic (LSK) approach, millions of ion trajectories are followed in the time-dependent MHD fields, starting from an ionospheric source. These particles undergo very complex orbits, some of them are on adiabatic bouncing orbits but a non-negligible fraction are non-adiabatically accelerated during neutral sheet crossings and supply part of the observed echoes.
DE: 2451 Particle acceleration
DE: 2704 Auroral phenomena (2407)
DE: 2744 Magnetotail
DE: 2760 Plasma convection (2463)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005