A new rocket range, SvalRak, was opened in November 1997 at Ny-A Ê lesund (79°N) in the Svalbard archipelago. The ®rst 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¯at trajectory through the lower D-region. The positive ion concentrations were larger than

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... , 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 ®ve 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¯ux 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.