LONG PERIOD (APPROXIMATELY 8-20 H) WIND OSCILLATIONS IN THE UPPER MIDDLE ATMOSPHERE AT SASKATOON (52-DEGREES-N) - EVIDENCE FOR NONLINEAR TIDAL EFFECTS

Winds measured by the Saskatoon MF radar (2.2 MHz) have been used to study atmospheric oscillations of periods greater than 1 h (e.g. inertio-gravity waves). Perturbations in the wind field are found by subtracting the mean day of the interval studied (6-11 days) from each day to form "difference" plots. In summer, below ∼ 90 km, the oscillations (10-20 m s-1) are extremely regular and coherent with height and time-inspection of the difference plots, and spectral and harmonic analysis, show these to be of 16 h period with λz of ∼ 10 km. It is probable that these are due to non-linear mixing of the 2-day wave and 12-h tide. In winter months, the oscillations are smaller and less regular, consistent with the superposition of inertio-GW of periods 8-20 h. © 1990.