HR: 0800h
AN: SM21A-0444    [Abstracts]
TI: Ionospheric Ion Beam Accelerations Above the Polar Cap
AU: * Maggiolo, R
EM: maggiolo@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: Fontaine, D
EM: dominique.fontaine@cetp.ipsl.fr
AF: CETP, 10, avenue de l'Europe, Velizy, 78140 France
AU: Teste, A
EM: alexandra.teste@cetp.ipsl.fr
AF: CETP, 10, avenue de l'Europe, Velizy, 78140 France
AU: Paschmann, G
EM: gep@mpe.mpg.de
AF: MPI, Giessenbachstrasse, Garching, D-85748 Germany
AU: Balogh, A
EM: a.balogh@imperial.ac.uk
AF: Imperial College, The Blackett Laboratory, London, SW7 2BZ United Kingdom
AU: Newell, P
EM: Pat.Newell@jhuapl.edu
AF: JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AU: Fazakerley, A
EM: anf@mssl.ucl.ac.uk
AF: MSSL, Holmbury St Mary, Dorking, RH5 6NT United Kingdom
AU: Reme, H
EM: reme@cesr.fr
AF: CESR, 9, avenue du Colonel Roche, Toulouse, 31028 France
AB: We present a Cluster multi-experiment study of near mono-energetic ion beams inside the polar cap. Data are taken at altitudes of 4 - 7 Re. Using the Cluster mass spectrometers a clear distinction is made between ion beams ejected from the polar cusp and those ejected along the local magnetic field line passing by the spacecraft. Polar cusp beams are characterized by the encounter of field aligned proton and oxygen ions with energies differing by a factor of about 4, as expected from the velocity filter effect. Polar cap local outflowing beams are characterized by a series of nearly monoenergetic ion inverted V structures in the 100 eV to ~ 3 keV range. Ions are field aligned and in many occasions the structures are associated with a converging electric field. The field aligned potential drop fits quite well the ion energy profile. No ion precipitation is recorded. In several cases comparisons of ion and electron distributions show that the parallel electric field is weak and can extend to altitudes higher than that of the satellite. Detailed analysis of the ion energy distribution show that oxygen ions are more energetic than protons and that outflowing ions are heated during their parallel acceleration. As for the auroral region, these observations could be due to an ion two-stream instability. We present the correlation of these events with the IMF orientation and use DMSP data to show the simultaneous occurrence of polar rain over the polar cap.
DE: 2451 Particle acceleration
DE: 2712 Electric fields (2411)
DE: 2776 Polar cap phenomena
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting