The Dynamics of the Mesosphere and Lower Thermosphere at Saskatoon (52°N)

Abstract

The dynamics of the upper Middle Atmosphere (60?110 km) over Saskatoon (52°N, 107°W) are described, using wind data from a medium frequency radar (2.2 MHz). Seasonal variations of gravity wave intensities (8 h-10 min) and tidal amplitudes and wavelengths (24 h-8 h) are considered. Below ?80 km, gravity wave amplitudes are larger (?100%) in winter than in summer months and there are equinoctial minima especially for short periods: tidal amplitudes are also slightly larger (?40%) in winter, but wavelengths are comparable with season. Between 80 and 95 km seasonal variations of gravity wave amplitudes are small, but above that height winter values are 40?100% greater. The tidal amplitudes vary in similar fashion, mainly due to large semidiurnal tides above ?90 km. Winter tidal wavelengths also tend to be shorter than in summer above 80 km altitude. These results are compared with recent data from other middle to high-latitude radar observatories: Monpazier (44°N), Christchurch (44°S), Poker Flat (65°N) and Eiscat (68°N). More data are required to firmly establish latitudinal variations of the seasonal dynamics of the upper Middle Atmosphere.