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Ann. Geophys., 16, 1355-1366, 1998
www.ann-geophys.net/16/1355/1998/
© European Geosciences Union 1998
Mesospheric observations with the EISCAT UHF radar during polar cap absorption events:
3. Comparison with simultaneous EISCAT VHF measurements
P. N. Collis1 and M. T. Rietveld2
1EISCAT Scientific Association, Box 812, S-981 28 Kiruna, Sweden
2EISCAT Scientific Association, Ramfjordmoen, N-9020 Tromsdalen, Norway
Abstract. Mesospheric observations were obtained by the
EISCAT UHF and VHF radars during the solar proton event of March 1990. We
present the first comparison of incoherent-scatter spectral measurements from
the middle mesosphere using simultaneous, co-located observations by the two
radars. VHF spectra observed with a vertical antenna were found to be
significantly narrower than model predictions, in agreement with earlier UHF
results. For antenna pointing directions that were significantly away from the
vertical, the wider VHF radar beam gave rise to broadening of the observed
spectra due to vertical shears in the horizontal wind. In this configuration,
UHF spectral measurements were found to be more suitable for aeronomical
applications. Both radar systems provide consistent and reliable estimates of
the neutral wind. Spectral results using both the multipulse and pulse-to-pulse
schemes were intercompared and their suitability for application to combined
mesosphere – lower thermosphere studies investigated.
Key words. Mesophere · Lower thermosphere · EISCAT
UHF radar · EISCAT VHF radar
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