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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 12
Ann. Geophys., 23, 3699–3713, 2005
https://doi.org/10.5194/angeo-23-3699-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 3699–3713, 2005
https://doi.org/10.5194/angeo-23-3699-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  23 Dec 2005

23 Dec 2005

Wave particle interactions in the high-altitude polar cusp: a Cluster case study

B. Grison1, F. Sahraoui1, B. Lavraud2, T. Chust1, N. Cornilleau-Wehrlin1, H. Rème3, A. Balogh4, and M. André5 B. Grison et al.
  • 1Centre d’étude des Environnements Terrestre et Planétaires, 10/12 avenue de l’Europe, 78140, Vélizy, France
  • 2Space Science and Applications Los Alamos National Laboratory, MS D466, Los Alamos, NM 87545, USA
  • 3Centre d’Etude Spatiale des Rayonnements, 9 avenue du Colonel, 31028 Toulouse Cedex 4, France
  • 4Space and Atmospheric Group, The Blackett laboratory, Imperial College, Prince Consort road, London, UK
  • 5Swedish Institute of Space Physics, Uppsala, Sweden

Abstract. On 23 March 2002, the four Cluster spacecraft crossed in close configuration (~100 km separation) the high-altitude (10 RE) cusp region. During a large part of the crossing, the STAFF and EFW instruments have detected strong electromagnetic wave activity at low frequencies, especially when intense field-aligned proton fluxes were detected by the CIS/HIA instrument. In all likelihood, such fluxes correspond to newly-reconnected field lines. A focus on one of these ion injection periods highlights the interaction between waves and protons. The wave activity has been investigated using the k-filtering technique. Experimental dispersion relations have been built in the plasma frame for the two most energetic wave modes. Results show that kinetic Alfvén waves dominate the electromagnetic wave spectrum up to 1 Hz (in the spacecraft frame). Above 0.8 Hz, intense Bernstein waves are also observed. The close simultaneity observed between the wave and particle events is discussed as an evidence for local wave generation. A mechanism based on current instabilities is consistent with the observations of the kinetic Alfvén waves. A weak ion heating along the recently-opened field lines is also suggested from the examination of the ion distribution functions. During an injection event, a large plasma convection motion, indicative of a reconnection site location, is shown to be consistent with the velocity perturbation induced by the large-scale Alfvén wave simultaneously detected.

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