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C. E. Meek and A. H. Manson

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 (uw′) 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.

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A. H. Manson and C. E. Meek

Abstract

The dynamics of the upper Middle Atmosphere (60–110 km) over Saskatoon (52°N, 107°W) are described, using wind data from a medium frequency radar (2.2 MHz). Seasonal variations of gravity wave intensities (8 h-10 min) and tidal amplitudes and wavelengths (24 h-8 h) are considered. Below ∼80 km, gravity wave amplitudes are larger (≲100%) in winter than in summer months and there are equinoctial minima especially for short periods: tidal amplitudes are also slightly larger (∼40%) in winter, but wavelengths are comparable with season. Between 80 and 95 km seasonal variations of gravity wave amplitudes are small, but above that height winter values are 40–100% greater. The tidal amplitudes vary in similar fashion, mainly due to large semidiurnal tides above ∼90 km. Winter tidal wavelengths also tend to be shorter than in summer above 80 km altitude.

These results are compared with recent data from other middle to high-latitude radar observatories: Monpazier (44°N), Christchurch (44°S), Poker Flat (65°N) and Eiscat (68°N). More data are required to firmly establish latitudinal variations of the seasonal dynamics of the upper Middle Atmosphere.

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A. H. Manson and C. E. Meek

Abstract

Wind data from approximately 75–110 km for the years 1972–75 have been obtained by the radiowave partial reflection drift technique. A summary of data which have appeared in earlier papers, and which relate to internal gravity (IG) waves, is given; and some of these data are subjected to additional analysis. Several of the new results reinforce the earlier interpretation, which involves coupling between IG waves and the mean flow. Associations are also found between IG wave amplitudes and the heights of reversals of the westward mean winds during autumn months of 1974; similar associations have been found previously for spring mouths. A related comparison between the magnitudes of the zonal and meridional components of the IG waves suggests important seasonal variations in the phase velocities of waves incident upon the mesosphere. Spectral analysis techniques are used to show the coherence of IG wave modes (20≲τ≲120 min) within the mesosphere and thermosphere.

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A. H. Manson and C. E. Meek

Abstract

The wind field of the middle atmosphere (60-100 kin) is sampled by the Saskatoon Medium Frequency radar: temporal resolution is normally 5 rain, and vertical is 1.5/3 kin. Profiles are analyzed for gravity waves (GW), and periods r from 10 rain-10 h are measured, with 3,z > 2 km and amplitudes > 5 m s-. The profiles are quite similar to those from rocket soundings. Wind vector shears are also consistent with "wind corners" evident in recent rocket data. Vertical shears of the horizontal wind and GW amplitudes (10 < r < 60 rain)are calculated and shown as annual height-time cross sections; values near 60 km are compared with rocket data from nearby Primrose Lake. Regions favoring dynamic and convective instability and GW saturation are located. The scattered radar power is shown as a seasonal cross section and compared to the shear and GW features. Finally, the dissipation rate of GW kinetic energy is calculated and compared with related MF radar and rocket wind estimations.

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A. H. Manson and C. E. Meek

Abstract

Gravity waves (GW) have been detected and their characteristics measured by observations with the Saskatoon multiple bistatic system, Gravnet. Data are available from 50 days for two height ranges 64–97 km, ∼100–115 km, and for the four seasons of 1983–85. Wave characteristics include horizontal wavelength, phase velocity, period, and amplitude. Background wind data allows the corresponding intrinsic parameters to be calculated; many waves are Doppler shifted to near their critical levels. Altitude and seasonal variations in the GW characteristics are shown. The strongest variation is in the horizontal direction of wave propagation, with southward directions dominating, but significant eastward(westward) fluxes in summer(winter) below 100 km.

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A. H. Manson, C. E. Meek, and J. B. Gregory

Abstract

Observations of the semi-diurnal atmospheric tide have been made on a continuous daily basis since September 1978 by a medium frequency (MF) radar. The monthly mean zonal winds and tidal amplitudes and phases (70–110 km), are shown here for each month of the autumn and spring equinoxes (1981–82), and compared with previous years. A very regular and dramatic tidal pattern emerges, with March and November being winter-like, and the remaining four months being more summer-like. Wavelengths for the latter are 60–95 km, intermediate between winter (∼45 km) and summer (∼180 km) values. The less systematic and extended observations from other North American and European radar systems are consistent with these results when they are treated on a monthly rather than a seasonal basis.

The equinoctial spectral model of Walterscheid and DeVore (1981), which uses improved heating rates and realistic mean winds and temperatures, is compared with the new observations. The model is quite successful in producing wavelengths of 70–90 km, comparable amplitudes to the observational and phases of eastward maxima within 1–3 hours of the observations. However, the model does not explain the differences between spring and autumn equinoxes, nor does it address the large and regular monthly changes within each equinox.

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R. J. Stening, C. E. Meek, and A. H. Manson

Abstract

Six years of winds data measured by the partial reflection drifts technique have been analyzed for lunar tides. Data are available at 3 km intervals of height and are separately analyzed in two year datasets to cheek consistency. A month-by-month seasonal variation is derived. Largest amplitudes of the lunar tide occur in January–February with a smaller maximum in summer. The vertical wavelength is longest in summer, and the tide then resembles that predicted for a pure (2, 2) mode. In winter vertical wavelengths range from 25 to 81 km in different years. Several of these results do not agree with the model of Forbes. An O1 component of the lunar tide could not be detected.

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R. J. Stening, C. E. Meek, A. H. Manson, and D. G. Stephenson

Abstract

The results of partial reflection radiowave wind observations (60-110 km) for four 10-day intervals in 1976 at Saskatoon, Canada (52°N, 107°W), are presented. A harmonic analysis has been applied to data for the four seasons: the means of the semi-diurnal and diurnal components are in reasonable agreement with other measurements at similar latitudes. There are large day-to-day variations in the amplitudes and phases of the tides. The seasonal variations of mean winds (Gregory and Manson, 1975a) are not appreciably altered by the removal of tidal components. Gravity waves with periods ∼5 h are identified and the periods are found to vary with the mean background wind. The mechanism involved is not understood. An oscillation with a 2-day period is found in August and a similar oscillation is seen in stratospheric temperatures near 20 km.

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J. B. Gregory, C. E. Meek, A. H. Manson, and D. G. Stephenson

Abstract

The drifts technique derives wind vectors from correlation analysis of spatial and temporal sequences of radiowave field strength at ground level. The paper examines the bases of the analysis, and presents a new method (simplified Gaussian correlation analysis) suitable for large-scale processing. Evaluation of the quality of derived winds vectors by means of internal consistency measurements is described. Methods of editing are surveyed, and a new method, based on the normalized time discrepancy, is demonstrated. Methods for securing maximum yield of winds vectors from raw data are described. The use of microprocessors for immediate data processing is outlined. Comparisons of winds obtained by the partial reflection technique with other experimental techniques are examined.

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A. H. Manson, J. B. Gregory, C. E. Meek, and D. G. Stephenson

Abstract

The behavior of the daily noon winds at 52°N, 107° W (Saskatoon, Canada) at altitudes from 52 km to about 110 km are studied for the interval September 1974–Apzil 1975. These data are compared with ROCOB temperatures and winds (≲55 km) for Churchill (94°N, 59°W). The thermal wind equation and running cross-correlation analysis are used to demonstrate the seasonal variations of the meridional temperature gradient, and of coupling, within the stratosphere, mesosphere and thermosphere. The effects of the stratospheric warming of January 1975 are also investigated. The correlations were dominated by this event, and show that coupling occurred between the stratosphere (20–30 mb) and mesosphere/thermosphere (≲100 km) during the first half of January. Spectral analysis for two intervals before and after the stratwarm show that coupling was more significant during the late winter; periods near 2–3, 4–5 and ≳20 days were involved.

Comparisons between daily mean winds and daily noon winds show that up to 100 km the daily variations are well represented by the noon data; above 100 km the daily variations are less reliable but trends are well represented by the noon data.

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