Articles | Volume 22, issue 7
Ann. Geophys., 22, 2325–2335, 2004

Special issue: Spatio-temporal analysis and multipoint measurements in space...

Ann. Geophys., 22, 2325–2335, 2004

  14 Jul 2004

14 Jul 2004

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

K. Meziane1, C. Mazelle2, M. Wilber3, D. LeQuéau2, J. P. Eastwood4, H. Rème2, I. Dandouras2, J. A. Sauvaud2, J. M. Bosqued2, G. K. Parks3, L. M. Kistler5, M. McCarthy6, B. Klecker7, A. Korth8, M.-B. Bavassano-Cattaneo9, R. Lundin10, and A. Balogh4 K. Meziane et al.
  • 1Physics Department, University of New Brunswick, Canada
  • 2Centre d’Etudes Spatiales des Rayonnements, 9 Avenue du Colonel Roche, Toulouse, 31028, France
  • 3Space Sciences Laboratory, University of California, Berkeley 94720, USA
  • 4Space and Atmospheric Physics, The Blackett Laboratory, Imperial College, London, SW7 2BW, UK
  • 5Space Science Center, University of New Hamshire, Durham, 03824, USA
  • 6Earth and Space Sciences, University of Washington, Seattle, 98195, USA
  • 7MPI für Extraterrestrische Physik, Garching, 85741, Germany
  • 8MPI für Aeronomie, Katlenburg-Lindau, 37191, Germany
  • 9CNR-IFSI, Roma, 00133, Italy
  • 10Swedish Institute of Space Physics, Kiruna, 98128, Sweden

Abstract. 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 Re from the shock and the averaged bow shock θBn0 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 α0Bn0, 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 θBn 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 θBn angles are less than ~40°, consistent with the specular reflection hypothesis as the production mechanism of ions.