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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 20, issue 12
Ann. Geophys., 20, 1943–1958, 2002
https://doi.org/10.5194/angeo-20-1943-2002
© Author(s) 2002. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 20, 1943–1958, 2002
https://doi.org/10.5194/angeo-20-1943-2002
© Author(s) 2002. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 Dec 2002

31 Dec 2002

A statistical study of ion energization at 1700 km in the auroral region

M. Hamrin1, P. Norqvist1, T. Hellström2, M. André3, and A. I. Eriksson3 M. Hamrin et al.
  • 1Theoretical Physics, Umeå University, SE-901 87 Umeå, Sweden
  • 2Department of Computing Science, Umeå University, SE-901 87 Umeå, Sweden
  • 3Swedish Institute of Space Physics, Uppsala Division, Box 537, SE-751 21 Uppsala, Sweden
  • Correspondence to: M. Hamrin (hamrin@space.umu.se)

Abstract. We present a comprehensive overview of several potentially relevant causes for the oxygen energization in the auroral region. Data from the Freja satellite near 1700 km altitude are used for an unconditional statistical investigation. The data are obtained in the Northern Hemisphere during 21 months in the declining phase of the solar cycle. The importance of various wave types for the ion energization is statistically studied. We also investigate the correlation of ion heating with precipitating protons, accelerated auroral electrons, suprathermal electron bursts, the electron density variations, Kp index and solar illumination of the nearest conjugate ionosphere. We find that sufficiently strong broad-band ELF waves, electromagnetic ion cyclotron waves, and waves around the lower hybrid frequency are foremost associated with the ion heating. However, magnetosonic waves, with a sharp, lower frequency cutoff just below the proton gyrofrequency, are not found to contribute to the ion heating. In the absence of the first three wave emissions, transversely energized ions are rare. These wave types are approximately equally efficient in heating the ions, but we find that the main source for the heating is broadband ELF waves, since they are most common in the auroral region. We have also observed that the conditions for ion heating are more favourable for smaller ratios of the spectral densities SE /SB of the broadband ELF waves at the oxygen gyrofrequency.

Key words. Ionosphere (auroral ionosphere; wave propogation) Magnetospheric physics (electric fields)

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