Engineering topics

Meek, C. E.

Publications and source records attributed to Meek, C. E..

At least 19 records

NASA NTRS1991

Comparisons between satellite-derived gradient winds and radar-derived winds from the CIRA-86

The zonal and meridional wind contours in the 60-120 km region obtained from satellite radiance data were compared with radar-derived contours of winds obtained from the CIRA-1986 reference atmosphere. It was found that the agreement between the directly observed zonal winds and the zonal mean gradient winds from the reference atmosphere wind model was good, especially below 80 km. However, differences were found in both the Southern and the Northern Hemispheres.

Manson, A. H.↗

NASA NTRS1990

Comparison between reference atmosphere winds and radar winds from selected locations

Zonal and meridional 60-110-km wind profiles obtained by radar measurements at Saskatoon, Adelaide, Christchurch, Puerto Rico, and Mawson are presented graphically and compared with those from the COSPAR International Reference Atmosphere (CIRA) for 1986. Good general agreement is found below about 80 km, but above 80 km the CIRA 1986 models show discrepancies, including: (1) no spring tongue of weak westward flow at latitudes 20-70 deg; (2) too strong an eastward flow at 20-52 deg in summer; (3) too great reversal heights at 35-43 deg N in summer; and (4) too strong (by a factor of 2) summer and winter jets at 65-70 deg N.

Manson, A. H.↗

NASA NTRS1989

Global behavior of the height/seasonal structure of tides between 40 deg and 60 deg latitude

The radars utilized are meteor (2), medium frequency (2) and the new low frequency (1) systems: analysis techniques were exhaustively studied internally and comparatively and are not thought to affect the results. Emphasis is placed upon the new height-time contours of 24-, 12-h tidal amplitudes and phases, which best display height and seasonal structures; where possible high resolution (10 d) is used (Saskatoon), but all stations provide monthly mean resolution. At these latitudes the diurnal tide is generally smaller than the semidiurnal, and displays more variability. However, there is a tendency for vertical wavelengths and amplitudes to be larger during summer months. On occasions in winter and fall, wavelengths may be less than 50 km. The dominant semidiurnal tide shows significant regular season structure; wavelengths are generally small (about 50 km) in winter, large in summer (equal to or greater than 100 km), and these states are separated by rapid equinoctial transitions. There is some evidence for less regularity toward 40 deg. Coupling with mean winds is apparent. Data from earlier ATMAP campaigns are mentioned, and reasons for their inadequacies presented.

Manson, A. H.↗

NASA NTRS1989

Measurements of vertical motions by the Saskatoon MF radar (1983-1985): Relationships with horizontal winds and gravity waves

The continuing series of horizontal wind measurements by the spaced-antenna real time winds (RTW) method was supplemented by a phase coherent system for two years. Vertical motions are inferred from the complex autocorrelation functions, and an RTW system provides 5 min samples from 60 to 110 km. Comparisons with full interferometric 3-D velocity measurements confirm the validity of this approach. Following comparisons and corrections with the horizontal winds, mean summer and winter (24 h) days of vertical motions are shown. Tidal fluctuations are evident. In summer the motions are downward, consistent with data from Poker Flat, and the suggestion of Coy et al. (1986) that these represent Eulerian motions. The expected upward Lagrangian motion then results from adding up upward Stokes' drift. The winter motions are more complex, and are discussed in the context of gravity wave fluxes and possible meridional cells. The divergence of the vertical flux of zonal momentum is also calculated and found to be similar to the coriolis torque due to the meridional winds.

Manson, A. H.↗

NASA NTRS1989

Dynamics of the upper middle atmosphere (80-110 km) at Tromsoe, June-December 1987, using the Tromsoe/Saskatoon M.F. radar

A real time winds (RTW) system from Saskatoon operated with the Tromsoe M.F. (partial reflection) radar on a continuous basis, June to December 1987. Profiles with 3 km resolution were obtained every 5 minutes with weak ionization, and few geomagnetic disturbances limited the observations normally to 80 to 110 km. However, daily mean winds, tidal characteristics (24, 12 h) such as amplitudes, phases and wavelengths, and gravity wave characteristics (intensities, mean directions) are available throughout this interval, which includes MAC-SINE and Epsilon. This is particularly valuable in defining the background state for some experiments, e.g., rockets, and for comparison with related parameters from the lidar and other radars (EISCAT, SOUSY-VHF). Comparisons with dynamical parameters from Saskatoon (52 N) are made: the zonal circulation was weaker at Tromsoe, tidal amplitudes smaller, and summer 12 h tidal wavelengths shorter (approx. 80 km vs approx. 100 km). The fall transition for this tide occurred in September, earlier than observed elsewhere. Initial comparisons with other experimental systems are also made.

Manson, A. H.↗

NASA NTRS1986

Horizontal wind perturbations and their relation to transient internal gravity waves

Horizontal winds as measured with the Saskatoon MF radar exhibit wind fluctuations which have preferred directions toward north or south in the period range 0 to 60 min at heights between about 60 and 110 km. Longer period perturbations (approx 1-6 h) tend to have an additional maximum of direction frequencies in the E-W sector.The polarization effect analyzed for more than 6 years shows regular changes with season. The main features of the seasonal variations of the direction distributions can be explained by directional filtering of vertically propagating nonstationary gravity waves and appropriate changes of the wave source strength and position in the troposphere. The N-S polarization of the gravity-wave field appears to result in meridional wind reversals with height above the mesopause.

Ebel, A.↗

NASA NTRS1986

Comparison of medium frequency pulsed radar interferometer and correlation analysis winds, part 1

In principle, the interferometer analysis determines the radial velocity and direction of single scatterers provided that each has a sufficiently different Doppler frequency to permit separation by spectral analysis. In fact, scatterers will not have constant radial velocity, and their Doppler frequencies as well as their directions will be modulated by their horizontal motion. Thus, there is a tradeoff between the poorer resolution but less smeared scatterers on shorter records and the higher resolution (longer) records. Three or more non-collinear scatterers are sufficient to determine the wind. It appears that the velocity found from the combined interferometer peaks agrees well with the apparent velocity from correlation methods, but the true velocity is a factor of 2 smaller. This difference might be resolved by searching for scatters showing regular movement between adjacent records.

Meek, C. E.↗

NASA NTRS1986

Comparison of medium frequency pulsed radar interferometer and correlation analysis winds, part 2

In order to test whether the chosen Doppler peaks represent localized scatters in motion, as opposed to some sort of integrated composite, an attempt was made to determine the change in position of single scatterers over a series of sequential records. A four-antenna system was employed which had 1 degree of freedom in phase. Due to limitations N-S linear transmission and E-W linear reception were used. The Doppler frequency peak selection criteria were that at least two of the four power spectra should have a local peak, and that normalized phase discrepancy, should be less than 0.3. The lack of success in tracking individual scatters seems to suggest a short lifetime. If this is the case, then the present experiment is not able to resolve the difference found between the correlation analysis true velocity and the interferometer value. On the other hand, it appears that the interferometer may be of some use in tracking waves.

Meek, C. E.↗

NASA NTRS1986

Progress in the MF radar system at Saskatoon

Two improvements were made to the radar system in the last year, one was the addition of O/X mode capability to the full antenna array used in the real-time wind system, and the other was the development of a coherent receiver. The design of the transmitter antenna is examined. The proposed coherent real-time wind system is also discussed.

Meek, C. E.↗

NASA NTRS1985

Mean winds of the upper middle atmosphere (60-110 km): A global distribution from radar systems (M.F., METEOR, VHF)

Since the development of the last CIRA in 1972, the number of radars providing winds in the upper middle atmosphere has increased significantly. These systems fill the data gap between 60 km and 110 km. The radars include medium frequency (MF) radars or partial reflection systems giving data from 60/70 to 100/110 km; meteor radars, 80 to 110 km, and M.S.T. radars operating as meteor radars. Data from 12 locations are shown, which represent a good Northern Hemispheric (NH) North American chain, an Oceanian chain which is mainly in the Southern Hemisphere (SH), and some Western Europe data. Generally tidal oscillations have been removed from days or groups of days, and the remaining mean winds and longer period oscillations plotted as height-time contours. Composite cross sections from the years 1978 to 1982 were formed where possible so that only the major temporal features remain.

Manson, A. H.↗

NASA NTRS1985

Middle atmosphere (60-110 km) tidal oscillations at Saskatoon, Canada (52 deg N, 107 deg W) during 1983/84

Since mid-1978, the medium frequency (2.2 MHz; M.F.) radar at Saskatoon has run continuously, measuring winds by the spaced antenna method in the upper middle atmosphere. As there is so much dynamics activity during the years of MAP it seems very important to establish the features of the tidal field at Saskatoon during 1983 to 1984, and compare these with the climatology from the four years 1978 to 1979 and 1981 to 1982. Wind profiles with 60 to 110 km (80 to 110 km at night) with 3 km resolution are obtained every 5 minutes by means of a full-correlation analysis. Hourly means are formed and harmonic analysis applied to sets of data to obtain the mean winds and tidal oscillation amplitudes and phases. The zonal wind field at Saskatoon is structurally similar to CIRA-72; however, the wind eastward cell is weaker and much more structured, and the summer eastward cell above 85 km is also weaker. For the semidiurnal tide, a strong seasonal change exists, with larger amplitudes and shorter wavelengths, in winter-like months and the reverse in summer-like months. A summary of the tidal parameters at 90 km is given, where mean values from 1978 to 1982 are also shown. This seasonal variation of tides is a midlatitude climatology, as comparisons with Monpazier, France and Christchurch, New Zealand show very similar behavior, as does Durham; and requires antisymmetric tidal modes such as 2,3 and 2,5. Considering the diurnal tide, for most months centered on summer there are long wavelength modes, or superposition of several models. However, some winter months show a short wavelength mode. A summary of the 90 km characteristics is presented.

Manson, A. H.↗

NASA NTRS1985

Gravity waves observed with GRAVNET: Saskatoon (52 deg N, 107 deg W) 1983/84

The GRAVNET system is based on a medium frequency (MF) radar (2.22 MGz) with one site consisting of a transmitting and spaced receiving antenna; and two remote receiving sites (approximately 40 km distance, forming an approximately equalateral triangle), also spaced receiving antennas. The winds of the upper middle atmosphere (60 to 110 km) are measured at each of the three sites in real time, using the Spaced Antenna method. Up to 12 profiles per hour were obtained. Spectral analysis was performed separately on northward and eastward velocity components for each site at the same height. Cross spectra are then found between sites. Data selection criteria included the Normalized Phase Discrepancy (NDP).

Meek, C. E.↗

NASA NTRS1985

Saskatoon M. F. Radar System: (52 Deg N, 107 Deg W), Canada

The system runs continuously, producing 1-h profiles approx. 75 to 110 km, 1978 to 1983: in particular for the 30-d (Nov. 9 to Dec. 7), 10-d (Nov. 16 to 26), 4-d core periods (Nov. 19 to 23). The means (EW, NS) and fourier components (24-, 12-h) fitted for the 4-d are shown. s.d. are shown, as derived from four 24-h fits in the interval. Comparisons with the 10-, 30-d intervals confirm confidence in these data and the lack of major variability in November. The 1-h profiles are means of 12 profiles so intrinsic errors are minimal. The 4-, 10-d fourier fits are compared and also the 30-d means from 48-h fits; in these amplitudes are N2+E2 as N/E approx. 1. Means differ slightly due to planetary wave activity; 24-h tides are variable in Novembers; and the 12-h variation is small less than 80 km. The final figure is a high resolution spectra for the November month: the 12-, 24-h dominate; the 8-h appears less than 100 km; and up to 90 km there is a 4-d oscillation.

Manson, A. H.↗

NASA NTRS1985

May 1982, Saskatoon M. F. Radar System: (52 Deg N, 107 Deg W), Canada

The system runs continuously, producing 1-h profiles approx. 75 to 110 km, 1978 to 1983: in particular for the 30-d (April 20 to May 19) centered on the inner core (May 3 to 6), 10-d (May 2 to 11). Incredibly, the only days missed for April/May were May 4/5, so 4-d fits for the core could not made! However the winds and tides were stable during May, so that the 10-d fits can be taken for comparison with other locations. The means (EW/NS) and Fourier components (24-, 12-h) for the 10-d (May 2 to 11) are shown; also those for the 30 days. Standard deviations are shown to be quite small. There is also little difference between 10- and 30-d profiles. The zonal flow is quite weak, showing that the summer westward flow has not fully developed. The 24-h tide has large lambda: approx. 100 km (EW and infinity (NS). Below 90 km the tide is circular, but above almost linear with EW amplitudes larger than NS. The 12-h tide is circular and lambda is small below 95 km; and more linear and variable above. The 30-d May spectral figure shows that 12-, 24-h tides are comparable; otherwise there is a 3.85-d oscillation to approx. 90 km; there were no other significant peaks.

Manson, A. H.↗

NASA NTRS1985

Mean Winds of the Mesosphere (60-80 Km), as Measured by MF Radars

Winds data obtained from medium frequency (MF) radars for heights of 60 to 80 km are discussed: locations are Saskatoon (52 N, 107 W), Christchurch (44 S, 173 W), Adelside (35 S, 183 E) and Townsville (20 S, 147 E). Whereas well defined summer easterly jets centered near 70 km develop in summer, no regular buildups and decays are observed in winter at midlatitudes. Part of this variability can be associated with stratospheric warmings, which develop into breakdown of the polar vortex in the Northern Hemisphere. Amplitude and phase profiles of the annual and semiannual oscillations are also presented. The radar winds from Saskatoon are compared and combined with rocket derived winds up to 60 km from Primrose Lake (54 N, 110 W) to give consistent cross sections from 20 to 110 km. The SH radar winds are compared with a model based on rocket winds which extends up to 80 km. The latter evidence considerable smoothing, as no winter variability is evident. The other consistent difference is that heights of the summer easterly maxima for the model are 5 to 10 km lower than the radar winds at all latitudes.

Manson, A. H.↗

NASA NTRS1985

Mean Winds of the Upper Middle Atmosphere (60-110 Km): a Global Distribution from Radar Systems (MF, Meteor, VHF)

During the last decade a large number of radars have been developed, which have produced substantial quantities of tidally corrected mean winds data in the upper middle atmosphere. The distribution of the radars is not global, but many areas are well covered. Zonal and meridional wind height-time cross sections from 60 to 80 km (MF/meteor radar) to approx. 110 km were preared for the last 5 to 6 years. They are compared with cross sections from CIRA 1972 for zonal winds, and GROVES (1969) for meridional winds. It is shown that while CIRA 1972 is still a useful model for many purposes, significant differences exist between it and the new radar data. The latter demonstrate important seasonal, latitudinal, longitudinal and hemispheric variations. The new meridional cross sections are of great value. The common features with GROVES (1969) are the equatorward cells in summer near 85 km; however, their strength (approx. 10 m/s) and size are less. Systematic and somewhat different variations emerge at (higher 52 N) and lower (35 to 44 deg) latitudes.

Manson, A. H.↗

NASA NTRS1984

A simple model for testing the effects of gravity-wave-produced vertical oscillations of scattering irregularities on spaced-antenna, horizontal drift measurements

It has been suggested that the velocities produced by the spaced antenna partial-reflection drift experiment may constitute a measure of the vertical oscillations due to short-period gravity waves rather than the mean horizontal flow. The contention is that the interference between say two scatterers, one of which is traveling upward, and the other down, will create a pattern which sweeps across the ground in the direction (or anti-parallel) of the wave propagation. Since the expected result, viz., spurious drift directions, is seldom, if ever, seen in spaced antenna drift velocities, this speculation is tested in an atmospheric model.

Meek, C. E.↗

NASA NTRS1984

Criteria for optimum spacing of spaced antenna, part 3.2A

There are many factors affecting the spaced antenna drift results, only one of which is antenna spacing. Generally, good results are obtained at MF for receiver antenna spacings of 1-1.5 lambda, and at VHF (e.g., SOUSY) for spacings approx. 6 lambda. Since one of the factors, local atmospheric/ionospheric conditions, are difficult to predict, this paper will be restricted to a short discussion of relevant factors, and methods for comparing various antenna/analysis configurations.

Meek, C. E.↗