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

Abstract

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 ∼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 ∼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 Saskatoon 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.