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Testing the hypothesis of the influence of neutral turbulence on the deduction of ambipolar diffusivities from meteor trail expansion
(Journal article; Peer reviewed; Tidsskriftartikkel, 2005-03-30)
Fading times of radar echoes from underdense meteor trails in the upper mesosphere/lower thermosphere are commonly used to determine ambipolar diffusivities and hence ambient temperature. Diffusivities are generally expected to increase exponentially with height through the region from which the meteor trail echoes are obtained, viz., typically 70-110km altitude for a ~30-MHz radar. In practice, ...
Maximilian Hell's geomagnetic observations in Norway 1769
(Research report; Forskningsrapport, 2005)
In the years 1768-1770 an expedition lead by the Austrian/Hungarian astronomer and Jesuit Father Maximilian Hell travelled to Vardø in the northernmost part of Norway. The main objective of the expedition was to observe the transit of Venus in June 1769. However, scientific investigations in several other fields were also performed, among them observations of the magnetic declination. From the ...
The red-sky enigma over Svalbard in December 2002
(Journal article; Tidsskriftartikkel; Peer reviewed, 2005-07-27)
On 6 December 2002, during winter darkness, an extraordinary event occurred in the sky, as viewed from Longyearbyen (78° N, 15° E), Svalbard, Norway. At 07:30 UT the southeast sky was surprisingly lit up in a deep red colour. The light increased in intensity and spread out across the sky, and at 10:00 UT the illumination was observed to reach the zenith. The event died out at about 12:30 UT. Spectral ...