ROLE OF ATMOSPHERIC WAVES (1.5 H-10 DAYS) IN THE DYNAMICS OF THE MESOSPHERE AND LOWER THERMOSPHERE AT SASKATOON (52-DEGREES-N, 107-DEGREES-W) DURING 4 SEASONS OF 1976

Partial reflection drift observations were made at Saskatoon, Canada (52°N) for four 10 day intervals in January, April, August and October, 1976. Soundings from 60-118 km were made, and the data analysed to give the amplitudes of planetary, tidal (24, 12 h) and internal gravity (I.G.) waves (1.5 ≲ τ ≲ 6 h). Energy densities and scale heights are calculated, and the relative magnitudes of these for the various waves are discussed with respect to height and season. Energy and momentum deposition for the I.G. waves are in the range 0.04-0.16 W kg-1, and 0.5-2.0 m s-1 h-1 respectively. The characteristics of the I.G. waves are studied on a daily basis, and it is shown that the measured frequency at a given height is a function of the background wind there. This effect is thought to be due to non-linear processes. Analysis of these data suggest that the waves of periods 1.5 ≲ τ ≲ 8 h have horizontal wavelengths, 300 < λ < 1300 km, phase speeds of 25-90 m s-1 and are frequently polarized. Under these conditions actual accelerations of the mean wind due to momentum deposition over periods of several days may approach the above calculated values. © 1979.