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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 19, issue 4
Ann. Geophys., 19, 411–424, 2001
https://doi.org/10.5194/angeo-19-411-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 19, 411–424, 2001
https://doi.org/10.5194/angeo-19-411-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 Apr 2001

30 Apr 2001

CUTLASS HF radar observations of high-velocity E-region echoes

M. V. Uspensky1,6, A. V. Koustov2, P. Eglitis3,1, A. Huuskonen4, S. E. Milan5, T. Pulkkinen1, and R. Pirjola1 M. V. Uspensky et al.
  • 1Finnish Meteorological Institute, Geophysical Research, PO Box 503, FIN-00101, Helsinki, Finland
  • 2Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, S7N SE2, Canada
  • 3Swedish Institute of Space Physics, PO Box 537, 751 21 Uppsala, Sweden
  • 4Finnish Meteorological Institute, Observational Services, PO Box 503, FIN-00101, Helsinki, Finland
  • 5Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
  • 6on leave from Murmansk State Technical University, Sportivnaya 13, Murmansk 183056, Russia

Abstract. A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms1 , while the other group had significantly larger velocities, of the order of 700 ms1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm1 ) and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.

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

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