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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 10
Ann. Geophys., 18, 1304–1315, 2000
© European Geosciences Union 2000
Ann. Geophys., 18, 1304–1315, 2000
© European Geosciences Union 2000

  31 Oct 2000

31 Oct 2000

A comparative study of winds and tidal variability in the mesosphere/lower-thermosphere region over Bulgaria and the UK

D. Pancheva2,1, P. Mukhtarov1, N. J. Mitchell2, A. G. Beard2, and H. G. Muller3 D. Pancheva et al.
  • 1Geophysical Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
  • 2The Department of Physics, The University of Wales, Aberystwyth, SY23 3BZ, UK
  • 3The University of Cranfield, The Royal Military College of Science, Shrivenham, Swimdon, SN6 8LA, UK

Abstract. Meteor radars located in Bulgaria and the UK have been used to simultaneously measure winds in the mesosphere/lower-thermosphere region near 42.5°N, 26.6°E and 54.5°N, 3.9°W, respectively, over the period January 1991 to June 1992. The data have been used to investigate planetary waves and diurnal and semidiurnal tidal variability over the two sites. The tidal amplitudes at each site exhibit fluctuations as large as 300% on time scales from a few days to the intra-seasonal, with most of the variability being at intra-seasonal scales. Spectral and cross-wavelet analysis reveals closely related tidal variability over the two sites, indicating that the variability occurs on spatial scales large compared to the spacing between the two radars. In some, but not all, cases, periodic variability of tidal amplitudes is associated with simultaneously present planetary waves of similar period, suggesting the variability is a consequence of non-linear interaction. Calculation of the zonal wave number of a number of large amplitude planetary waves suggests that during summer 1991 the 2-day wave had a zonal wave number of 3, but that during January–February 1991 it had a zonal wave number of 4.

Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

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