The quasi 16-day oscillations in the mesosphere and lower thermosphere at Saskatoon (52°N, 107°W), 1980-1996

The daily mean winds observed by the Saskatoon MF radar are used to investigate the quasi 16-day oscillations in the mesosphere and lower thermosphere. Based on the wind data (every 3 km from 58 to 105 km, hourly from 1980 to 1996), the wave amplitudes and phases of all periods (2-24 days) as a function of height and time of year are available. Among them the 16-day wave occurs there mostly in winter with a maximum at similar to 60-65 km and covers a large range of altitudes (up to 100 km); in summer, however, the 16-day wave is much weaker and confined to similar to 85 km and above. The vertical wavelength in winter tends to be very long, but in summer it is a little shorter. After further investigation we found that the 16-day waves are extremely sensitive to the background mean winds; this explains their penetration, preferably in the westerly flow, from the lower atmosphere to the mesosphere in winter, or through a presumed ducting from the Southern Hemisphere to the Northern Hemisphere in Saska toon summer. The year-by-year variations of the 16-day wave in this paper show little correlation with the winter stratospheric warming events but imply certain associations with the equatorial quasi-biennial oscillation both in winter and in summer. The global scale wave model has been run to get the annual (12 months) 16-day wave simulations from the ground to 200 km. The comparison with the observations at Saskatoon indicates good agreement in winter months but significant differences in summer.