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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 2
Ann. Geophys., 18, 215–222, 2000
https://doi.org/10.1007/s00585-000-0215-7
© European Geosciences Union 2000
Ann. Geophys., 18, 215–222, 2000
https://doi.org/10.1007/s00585-000-0215-7
© European Geosciences Union 2000

  29 Feb 2000

29 Feb 2000

Irregular structures observed below 71 km in the night-time polar D-region

E. V. Thrane2,1, T. A. Blix1, and K. R. Svenes1 E. V. Thrane et al.
  • 1Norwegian Defence Research Establishment, P O Box 25, NO-2027 Kjeller, Norway
  • E-mail: eivind-wilhelm.thrane@ffi.no
  • 2Institute of Physics, University in Oslo, P O Box 1048, Blindern, NO-0316 Oslo, Norway
  • Correspondence to: E. V. Thrane

Abstract. A new rocket range, SvalRak, was opened in November 1997 at Ny-Ålesund (79°N) in the Svalbard archipelago. The first instrumented rocket was launched on 20 November, 1997, at 1730 UT during geomagnetically quiet conditions. The payload was instrumented to measure plasma parameters in the mesosphere and lower thermosphere, but the payload only reached an altitude of 71 km. This resulted in a very flat trajectory through the lower D-region. The positive ion concentrations were larger than expected, and some unexpected plasma irregularities were observed below 71 km. The irregularities were typically 100 m in spatial extent, with plasma densities a factor of two to five above the ambient background. In the dark polar night the plasma below 71 km must consist mainly of positive and negative ions and the only conceivable ionising radiation is a flux of energetic particles. Furthermore only relativistic electrons have the large energies and the small gyro radii required in order to explain the observed spatial structure. The source of these electrons is uncertain.

Key words: Ionosphere (ionospheric irregularities; ionization mechanisms) - Magnetospheric physics (polar cap phenomena)

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