Bow shock specularly reflected ions in the presence of low-frequency electromagnetic waves: a case study

K. Meziane (1) , C. Mazelle (2) , M. Wilber (3) , D. Lequéau (2) , J. P. Eastwood (4) , H. Rème (2) , I. Dandouras (2) , J. A. Sauvaud (2) , J. M. Bosqued (2) , G. K. Parks (3) , L. M. Kistler (5) , M. Mccarthy (6) , B. Klecker (7) , A. Korth (8) , M.-B. Bavassano-Cattaneo (9) , R. Lundin (10) , A. Balogh (4)

1 Physics Department
2 CESR - Centre d'étude spatiale des rayonnements
3 SSL - Space Sciences Laboratory [Berkeley]
4 Space and Atmospheric Physics Group [London]
5 SSC - UNH Space Science Center [Durham]
6 Department of Earth and Space Sciences [Seattle]
7 MPE - Max-Planck-Institut für Extraterrestrische Physik
8 MPI Aeronomie - Max-Planck-Institut für Aeronomie
9 IFSI - Istituto di Fisica dello Spazio Interplanetario
10 IRF - Swedish Institute of Space Physics [Kiruna]

An energetic ion (E=40) event observed by the CLUSTER/CIS experiment upstream of the Earth's bow shock is studied in detail. The ion event is observed in association with quasi-monochromatic ULF MHD-like waves, which we show modulate the ion fluxes. According to three statistical bow shock position models, the Cluster spacecrafts are located at ~0.5 R_e from the shock and the averaged bow shock ?_Bn0 is about ~30°. The analysis of the three-dimensional angular distribution indicates that ions propagating roughly along the magnetic field direction are observed at the onset of the event. Later on, the angular distribution is gyrophase-bunched and the pitch-angle distribution is peaked at a₀~?_Bn0, consistent with the specular reflection production mechanism. The analysis of the waves shows that they are left-handed in the spacecraft frame of reference (right-handed in the solar wind frame) and propagate roughly along the ambient magnetic field; we have found that they are in cyclotron-resonance with the field-aligned beam observed just upstream. Using properties of the waves and particles, we explain the observed particle flux-modulation in the context of ?_Bn changes at the shock caused by the convected ULF waves. We have found that the high count rates coincide with particles leaving the shock when ?_Bn angles are less than ~40°, consistent with the specular reflection hypothesis as the production mechanism of ions.

Domaines: Océan, Atmosphère; Sciences de la Terre

K. Meziane, C. Mazelle, M. Wilber, D. Lequéau, J. P. Eastwood, et al.. Bow shock specularly reflected ions in the presence of low-frequency electromagnetic waves: a case study. Annales Geophysicae, 2004, 22 (7), pp.2325-2335. ⟨hal-00329332⟩