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A. H. Manson

Abstract

The 1963 final spring warming in the antarctic stratosphere is discussed, with particular reference to the energy flux of electrons precipitated during the event. Temperature changes occurring throughout the atmosphere at this time are estimated. The change in thermospheric temperature (˜110 km) due to particle influx is shown to be approximately 15 K, when allowance is made for losses due to molecular conductivity, eddy transport and radiation. It is shown that this heating could lead to a greater deposition of gravity wave energy near 110 km in the auroral zone, and a further increase in local temperature. The resulting changes in the mid-latitude zonal wind above 80 km would lead to a modification in the large-scale wave activity at these heights. Although these mechanisms do not appear to constitute an initial triggering mechanism for the planetary wave which was associated with the stratospheric warming of 1963, they could lead to a correlation between the particle influx, and the mid-latitude stratospheric and thermospheric parameters.

Considerations of the photochemistry of ozone, as it is presently understood, suggest that the auroral emissions were too weak to introduce a mesospheric-stratospheric temperature perturbation capable of destabilizing the dynamic structure of that region. A more detailed knowledge of the photochemistry of ozone at heights up to 110 km, during particle influx events, should lead to a better understanding of the dynamics of this region. Finally, it is noted that there is insufficient atmospheric data to confirm the hypothesis that auroras or particle influx events are responsible for the onset of stratospheric warmings.

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A. H. Manson

Abstract

During 1985–86 a summary and review of gravity wave measurements was made by Reid. In particular a collation of 408 horizontal wavelengths was prepared, which included values from optical and radar methods. Since that time substantial new datasets have emerged from the Medium Frequency radars at Adelaide and Saskatoon, and from the CEDAR lidar at Urbana. These data are combined with the earlier collation to form composite figures. Questions are raised about the selectivity of the sounding systems.

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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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J. B. Gregory and A. H. Manson

Abstract

The behavior of winds at 52°N, 107°W (Saskatoon, Canada) at altitudes to ∼110 km during major stratospheric warmings of 1969–70,1970–-71 and 1972–73 winters and a minor warming in December 1972, is studied. The zonal component of flow above the stratosphere is found to be affected to varying altitudes; in January 1970 the normal eastward flow was reversed to westward at all altitudes from the surface to ∼110 km. The pattern of winds is reasonably consistent with current suggestions that at middle and high latitudes the mesosphere cools as the stratosphere warms, and that the mesosphere warms subsequent to its cooling. Examples of mesospheric wind perturbations either as precursors of stratospheric warmings or independent of warmings, are also given.

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J. B. Gregory and A. H. Manson

Abstract

The results of radiowave partial reflection wind (drift) observations, 62–116 km, for the years 1969–73, at 52°N, 107°W (Saskatoon), are presented, and are compared with current empirical models. Agreement is satisfactory to 85 km; but at higher altitudes, differences exist; notably an annual variation of zonal flow above 100 km, whose direction is eastward in summer and westward in winter. The semi-annual variation of winds is shown to be limited to 85–100 km, and is considered to be due to two out-of-phase annual variations identifiable at higher and lower altitudes. A region of positive (poleward) temperature gradient (high-latitude warming) is identified in the range ∼80 to at least 107 km in winter, and another region (∼75 to ≳107 km) of negative temperature gradient is identified in summer. The relationships of these regions to circulation characteristics are discussed.

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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, J. B. Gregory, and D. G. Stephenson

Abstract

Measurements of winds (60–110 km) for Saskatoon, Canada (52N, 107W), have been obtained from a partial reflection radiowave system. Closely spaced atmospheric soundings (12 per hour) for heights between 51–117 km with 3–km height resolution, were made between August 1972 and September 1973. The median of the wind profiles for a given hour has been identified mainly as the prevailing wind, and the irregular components from each profile as internal atmospheric gravity waves (30<τ<60 min, 12<λ<30 km). The amplitudes and shears of the irregular winds have their largest values in winter. A diurnal variation has been found, showing a minimum in amplitude and shear values near noon for all seasons; this variation is especially noticeable above 90 km.

Comparisons of seasonal variations in the prevailing zonal and meridional winds, with the amplitudes of the irregular winds, suggest interactions involving critical layers and momentum transfer. Tropospheric weather systems are considered in relation to the gravity wave amplitudes.

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