THE WIND REGIME OF THE MESOSPHERE AND LOWER THERMOSPHERE DURING THE DYANA CAMPAIGN .2. SEMI-DIURNAL TIDE

Co-ordinated ground-based radar measurements carried out during the 15 January-15 March 1990 DYANA campaign at 14 different geographical sit es 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 sig nificant 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 scale s do not contradict the hypothesis about a possible coupling between t hese oscillations and the low wave-number processes in the stratospher e. Tidal parameter oscillations with 2-5-day periods may be explained to be effects of the nonstationary processes with longitudinal wave nu mbers S > 3.