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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 3
Ann. Geophys., 22, 829–847, 2004
https://doi.org/10.5194/angeo-22-829-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 829–847, 2004
https://doi.org/10.5194/angeo-22-829-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  19 Mar 2004

19 Mar 2004

HF radar observations of high-aspect angle backscatter from the E-region

S. E. Milan1, M. Lester1, T. K. Yeoman1, T. R. Robinson1, M. V. Uspensky2, and J.-P. Villain3 S. E. Milan et al.
  • 1Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
  • 2Finnish Meteorological Institute, Geophysical Research, FIN-00101, Helsinki, Finland
  • 3Centre National de la Recherche Scientifique, Orléans, F-45045, France

Abstract. We present evidence for the observation of high-aspect angle HF radar backscatter from the auroral electrojets, and describe the spectral characteristics of these echoes. Such backscatter is observed at very near ranges where ionospheric refraction is not sufficient to bring the sounding radio waves to orthogonality with the magnetic field; the frequency dependence of this propagation effect is investigated with the Stereo upgrade of the CUTLASS Iceland radar. We term the occurrence of such echoes the "high-aspect angle irregularity region" or HAIR. It is suggested that backscatter is observed at aspect angles as high as 30°, with an aspect sensitivity as low as 1dB deg–1. These echoes are distinguished from normal electrojet backscatter by having low Doppler shifts with an azimuthal dependence that appears more consistent with the direction of the convection electric field than with the expected electron drift direction. This is discussed in terms of the linear theory dispersion relation for electrojet waves.

Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; auroral ionosphere)

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