Vertical Motions in the Upper Middle Atmosphere from the Saskatoon (52°N, 107°W) M.F. Radar

Abstract

The Saskatoon M.F. radar (52°N, 107°W) was operated in a Doppler mode to measure the vertical motions in the middle atmosphere (60?110 km). The 5-min and 1-h mean velocities were accumulated for a full calendar year. Mean 24-h days are formed into height-time velocity contours for summer and winter seasons, and corrections made to minimize contamination by horizontal winds. There are quite large diurnal oscillations (?0.2 m s?1) near 75 and 110 km, and residual daily mean values of 0.2?0,5 m s?1. In summer these latter are downward, consistent with an upward Stokes drift associated with gravity waves. However in winter the mean motions are upward (downward) below (above) 85 km. These upward winter results, also seen at Poker Flat (65°N) at all altitudes, are not easily explained. The divergence of the upward flux of horizontal momentum (u?w?) is calculated and found to provide accelerations (10?50 m s?1/day) consistent with the Coriolis torque on the meridional wind throughout the middle atmosphere.