HR: 0830h
AN: SH21B-0123    [PDF]
TI: Observations of a sharp boundary between field-aligned beams and gyrating ions in the foreshock
AU: Meziane, K
EM: karim@unb.ca
AF: Physics Department, University of New-Brunswick, Fredericton, NB E3B 5A3 Canada
AU: * Wilber, M
EM: wilber@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: Mazelle, C
EM: mazelle@cesr.fr
AF: CESR, 9, Avenue du Colonel Roche, Toulouse, 31028 France
AU: LeQueau, D
EM: lequeau@cesr.fr
AF: CESR, 9, Avenue du Colonel Roche, Toulouse, 31028 France
AU: Parks, G K
EM: parks@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AU: Reme, H
EM: reme@cesr.fr
AF: CESR, 9, Avenue du Colonel Roche, Toulouse, 31028 France
AU: Sauvaud, J
EM: sauvaud@cesr.fr
AF: CESR, 9, Avenue du Colonel Roche, Toulouse, 31028 France
AU: Dandouras, I
EM: dandouras@cesr.fr
AF: CESR, 9, Avenue du Colonel Roche, Toulouse, 31028 France
AU: Bosqued, J
EM: bosqued@cesr.fr
AF: CESR, 9, Avenue du Colonel Roche, Toulouse, 31028 France
AU: Kistler, L M
EM: lynn.kistler@unh.edu
AF: Space Science Center, University of New Hampshire, Durham, NH 03824 United States
AU: Klecker, B
EM: bek@mpe.mpg.ge
AF: MPI feur extraterrestrische Physik, POB 1312, Garching, 85741 Germany
AU: Korth, A
EM: korthsprotte@mpae.gwdg.de
AF: MPI feur Aeronomie, Max-Planck-Str 2, Katlenburg-Lindau, 37191 Germany
AU: McCarthy, M
EM: mccarthy@geophys.washington.edu
AF: Earth and Space Sciences, University of Washington, Seattle, WA 98195 United States
AU: Bavassano-Cattaneo, M B
EM: bice@ifsi.rm.cnr.it
AF: IFSI-CNR, Area di Ricerca di Toz Vergata Via del Fosso del Cavaliere, Roma, 00133 Italy
AU: Lundin, R
EM: rickard.lundin@irf.se
AF: Swedish Institute of Space Physics, Box 812, Kiruna, 98128 Sweden
AU: Eastwood, J
EM: j.p.eastwood@ic.ac.uk
AF: The Blackett Laboratory, Imperial College, Prince Consort Rd., London, SW7 2BW United Kingdom
AU: Balogh, A
EM: a.balogh@ic.ac.uk
AF: The Blackett Laboratory, Imperial College, Prince Consort Rd., London, SW7 2BW United Kingdom
AB: We report an observation by Cluster-CIS of an energetic (2--30~keV) upstream ion event presenting a clear double-peak spectrum. The lower-energy ($E\sim~3.5$~keV) peak is associated with an ion beam propagating along the magnetic field direction, while the higher-energy peak is associated with gyrating ions. Our analysis indicates that the gyrating ions had guiding centers on field lines downstream of the field-aligned component, but that both populations could be sampled simultaneously due to gyroradius effect. We find that downstream limit of the field-aligned beams is populated with protons having a speed 1.5 times the solar wind velocity, which is inconsistent with any known shock-related emission mechanisms. The spatial boundary separating the field-aligned beams from the gyrating ion guiding centers corresponds well with the ULF and intermediate ion foreshock boundary reported in previous studies. Like the field-aligned beams, the gyrating ions reported here have streaming speeds inconsistent with any known shock emission mechanisms. They probably result from instabilities excited by the propagation of field-aligned beams present just upstream. Our interpretation of these observations provides a refinement of the usual framework for foreshock morphology.
DE: 2116 Energetic particles, planetary
DE: 2134 Interplanetary magnetic fields
DE: 2154 Planetary bow shocks
DE: 2164 Solar wind plasma
DE: 7867 Wave/particle interactions
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting