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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, 3739–3752, 2005
https://doi.org/10.5194/angeo-23-3739-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 3739–3752, 2005
https://doi.org/10.5194/angeo-23-3739-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  23 Dec 2005

23 Dec 2005

Cluster observations and theoretical identification of broadband waves in the auroral region

M. Backrud-Ivgren1,2, G. Stenberg3, M. André1,2, M. Morooka1, Y. Hobara4, S. Joko4, K. Rönnmark3, N. Cornilleau-Wehrlin5, A. Fazakerley6, and H. Rème7 M. Backrud-Ivgren et al.
  • 1Swedish Institute of Space Physics, Box 537, 751 21 Uppsala, Sweden
  • 2Dept. of Astronomy and Space Physics, Uppsala University, Box 515, 751 20 Uppsala, Sweden
  • 3Department of Physics, Umeå University, 901 87 Umeå, Sweden
  • 4Swedish Institute of Space Physics, Box 812, 981 28 Kiruna, Sweden
  • 5CETP/CNRS, University of Versailles Saint Quentin, 10-12 Av. De l’Europe, 78140 Vélizy, France
  • 6The Mullard Space Science Laboratory, University College London, Holmbury St. Mary Dorking, Surrey, RH5 6NT, UK
  • 7Centre d’Etude Spatiale des Rayonnements, 9 avenue du Colonel Roche Toulouse, France

Abstract. Broadband waves are common on auroral field lines. We use two different methods to study the polarization of the waves at 10 to 180 Hz observed by the Cluster spacecraft at altitudes of about 4 Earth radii in the nightside auroral region. Observations of electric and magnetic wave fields, together with electron and ion data, are used as input to the methods. We find that much of the wave emissions are consistent with linear waves in homogeneous plasma. Observed waves with a large electric field perpendicular to the geomagnetic field are more common (electrostatic ion cyclotron waves), while ion acoustic waves with a large parallel electric field appear in smaller regions without suprathermal (tens of eV) plasma. The regions void of suprathermal plasma are interpreted as parallel potential drops of a few hundred volts.

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