The wind regime of the mesosphere and lower thermosphere during the DYANA campaign-II. Semi-diurnal tide

Co-ordinated ground-based radar measurements carried out during the 15 January-15 March 1990 DYANA campaign at 14 different geographical sites have provided a good opportunity to investigate the characteristics of semi-diurnal tidal variations in the mesosphere/lower thermosphere over a wide spectrum of space/time scales. It is pointed out that significant differences of monthly mean tidal parameters observed at the various sites may be explained by latitudinal and longitudinal effects. Well-defined 2-3-week oscillations of the tidal parameters are found to be typical of all observational sites. Their estimated space scales do not contradict the hypothesis about a possible coupling between these oscillations and the low wave-number processes in the stratosphere. Tidal parameter oscillations with 2-5-day periods may be explained to be effects of the nonstationary processes with longitudinal wave numbers S > 3. © 1994