ANGEO

Annales Geophysicae

ANGEO

Ann. Geophys.

1432-0576

Springer Verlag

Göttingen, Germany

10.1007/s00585-000-0215-7

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

Thrane

E. V.

³ ² ¹ ⁴ Blix

T. A.

² ¹ ⁴ Svenes

K. R.

² ¹ ⁴

Norwegian Defence Research Establishment, P O Box 25, NO-2027 Kjeller, Norway

E-mail: eivind-wilhelm.thrane@ffi.no

Institute of Physics, University in Oslo, P O Box 1048, Blindern, NO-0316 Oslo, Norway

Correspondence to: E. V. Thrane

29 02 2000

18 2 215 222

2000

This article is available from https://angeo.copernicus.org/articles/18/215/2000/angeo-18-215-2000.html

The full text article is available as a PDF file from https://angeo.copernicus.org/articles/18/215/2000/angeo-18-215-2000.pdf

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)