Characteristics of gravity waves (10 min‐6 hours) at Saskatoon (52°N, 107°W): Observations by the phase coherent medium frequency radar

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Abstract
Height‐time cross sections of the power spectral density in two bands (10–100 min, 2–6 hours) for gravity waves (IGW) are formed from horizontal (u, v) and vertical (w) wind measurements made during 1989 and 1990 using the Saskatoon MF radar (52N, 107W). These climatologies are compared with the seasonally varying mean winds, and are consistent with data from previous years (1979–1984), which demonstrated semiannual variations (solstitial maxima) below ∼90 km and annual (winter maximum) above 90 km. Directions of preferred propagation are inferred by forming the wind perturbation covariances and fitting ellipses to the perturbation velocities; the preferred orientations are closer to meridional (NS) than to zonal (EW) especially for the shorter periods. Finally the , products, which are the vertical fluxes of horizontal momenta, are formed in cross section and time series formats for the longer periods. The zonal momenta have a seasonal variation below 85 km apparently modulated by the zonal mean winds, with mainly westward/eastward momenta in winter/summer months. The divergences of the flux provide accelerations of +10 m s−1 d−1 in summer (65–80 km) and −15 ms−1 d−l in winter (75–90 km), which are somewhat less than (but often opposite in sign to) the Coriolis torque on the meridional flow. Such comparisons suggest that shorter period waves must also contribute important fluxes of momentum. The fluctuations in IGW intensities and covariances over time scales of several days may be considerable and will affect the sampling needed to obtain seasonal means. Fluctuations due to planetary waves and stratwarms are observed.

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