mf doppler and spaced antenna radar measurements of upper middle atmosphere winds

MF Doppler and spaced antenna radar meas~ements of upper middle atmosphere winds

IAIN M. REID

Max-Planck-Institut fi.ir Aeronomie, D-341 1 K~tlenburg-Lindau, F.R.G.

(Received infinal,fim 17 August 1987)

.A~~act~bse~ations of upper mesospheric and lower thermosphere wind velocities obtained simultaneously over six days with MF Doppler and Spaced Antenna (SA) radars at Adelaide, Australia in November 1980 are presented. To obtain these measurements, the large (_ 1 km diameter) Buckland Park MF array was run in a dual beam Doppler radar configuration, and a portable SA radar was operated adjacent to the main array. Hourly mean values of wind velocity show considerable consistency, with cross correlation coefficients of about O.&W? for the entire observational period. However, agreement between the magnitudes of the wind velocities as measured by each technique is found to be significantly improved when the effect of the aspect sensitivity of the backscattering irregularities on the effective beam pointing angle of the Doppler radar beams is taken into account. This is also found to be true for SA and Doppler radar observations obtained in adjacent periods of 2-5 days over two years with the Buckland Park facility operating alternatively as a Doppler and SA radar. Some representative examples of these results are also presented and discussed. A preliminary comparison between MF Doppler and SA radar derived vertical wind velocities is also briefly considered.

1. INTRODUCTlON

Intercomparison of different experimental techniques is essential, because this is the only way their suit- ability and limitations for particular applications may be rigorously determined. The two techniques that we consider here, the Spaced Antenna (SA) and Doppler radar techniques, are of particular interest, because they are both used to measure winds in the upper middle atmosphere (60-110km) at MF, and in the troposphere and stratosphere at VHF. The comparisons reported here concern only measurements of wind velocities in the 8&100 km height region made at MF, but some of the results are of general interest.

Most notable is the importance of the enhanced echo power received at MF and HF from the vertical for those Doppler radar measurements of wind velocities obtained using relatively wide beams which are directed off-vertical at angles of less than about 15”. Since the effective off-zenith angle of the beam is determined by the product of the polar diagrams of the radar array and the backscattering irregularities, it is often less than the apparent off-zenith angle, and the measured radial velocities are effectively underestimated. A similar enhancement in ba~kscattered power is also found in measurements at VHF in the lower atmosphere, and in the mesosphere, and so when wide beam widths are used, these results are also subject to error.

Recent observational studies using the Buckland

Park MF (I .98 MHz) radar facility as a Doppler radar have taken the effect into account (REID, 1984; REID and VINCENT, 1987a, b ; FRITTS and VINCENT, 1987). In this study, we examine Doppler and SA measurements of wind velocity in the 8&l 00 km height region obtained simultaneously over six days in November 1980 at Buckland Park, and in some representative observational periods obtained over a period of two years, for evidence of this effect.

2. ESTIMATION OF THE EFFECTIVE BEAM ANGLE

At D-region heights (- 6&100 km), scattering irregularities often exist in the form of thin horizontally stratified layers, and as a consequence, backscatter is returned only from angles close to the zenith. The scattering properties are observed to vary with height, and the D-region may be roughly divided into two regimes on the basis of the character of the backscatter. Below about 75-80 km, radar returns often appear to be due to specular type reflection from thin horizontal steps in refractive index, and these are observed to be both spatially and temporarily inte~ittent. LINDNER (1975a,b) and HOCKING (1979) at Adelaide (35’S), and JONES (1980) at Bris- bane (28”s) found that on average at 2 MHz, scatter was returned only from angles up to 2-6” from the zenith in this height range, and VINCENT and BELROSE (1978) found values of 7-9” in the W-80 km region at

117

118 I. M.

Ottawa (45”N). Above these heights, backscatter was found to be more isotropic in character, and was received from angles up to 15-20” from the zenith.

Similar results have been obtained at VHF by

R~~TTGER et al. (1979), FUKAO et al. (1980), and CZECHOWSKY et al. (1984). HOCKING (1987) has considered measurements such as these in a review of radar studies of small scale structures in the upper middle atmosphere. In addition, he has also considered measurements of the fading time (or equiv-

alently the spectral width) of backscattered radio waves to determine upper limits to values of O,, and found values in good agreement with the height distribution outlined above. In contrast to these results,

FRITTS and VINCENT (1987) found values of about 8- 16” below 80 km, and of about 6-7’ above this height at 2 MHz at Adelaide, suggesting less isotropic scatter above 80 km.

Whatever the actual height distribution, the importance of these observations is that when radar beams are used to observe backscatter, the effective beam

pointing direction is determined by the product of the angular polar diagrams of the backscatter and the

radar array. For a radar beam of finite width, and a backscatter polar diagram which is narrow about the zenith, this product yields an effective beam at a mean pointing angle (0,) such that radiation is received closer to the zenith than the apparent beam angle

(O,), and the measured radial velocity is an underestimate. If the beam width is narrow (- I”), the effective off-zenith angle cannot be changed much, and the resulting error is small. If the beam width is relatively large, as at Buckland Park say (4.5” half- power, half-width), large errors can result.

That such an effect would occur for aspect depen- dent backscatter appears to have been first noted by DONALDSON (1965), and is discussed in BROWNING and WEXLER (1968) in relation to meteorological radars. More recently, R~~TTGER (1981) and WHITE- HEAD et al. (1983) have considered its importance for Doppler radar. As suggested by these authors, if both the backscatter and radar receiving array angular polar diagrams are known, then it should be possible to correct for this effect. However, because the properties of the scattering medium may be changing quite rapidly, it may only be realistic to measure the mean angular width of the backscattered radiation over a suitably long period of time.

At Buckland Park, measurements have been made using both indirect (GOLLEY and ROSSITER, 1971; LINDNER, 1975a, b ; FRITTS and VINCENT, 1987 ; and see also HOCKING, 1987) and direct (HOCKING, 1979) methods. The best estimates are perhaps those made by Lindner, who measured the relative phase of back-

&ID

scattered radiation received at spaced antennae to

estimate its mean angular spread. They have an advantage over those of GOLLEY and ROSSITER (197 1)

and HOCKING (1979), in that they were obtained over

the entire 60-100 km height region in observational periods spaced over almost a year, and over those of FRITTS and VINCENT (1987) in that the mean result should represent a seasonal average. Agreement between the results of the studies by GOLLEY and ROSSITER (1971), LINDNER (1975b) and HOCKING

(1979) is good, but those of FRITTS and VINCENT (1987) are somewhat different at heights below about 80 km. Figure la attempts to illustrate the mean angu-

lar spread (O,,) from the zenith of backscattered radiation at 2 MHz determined in these studies. Here 0, is defined such that the power received at an angle 0 from the zenith is proportional to exp{ -(sin O/sin U,)‘}.

Lindner used two methods, which differed in

sophistication, but which gave essentially identical results. The solid line in Fig. la is a composite of

results he obtained between February and November 1971. Only two months, June and September, showed

the decrease in O,, above 90 km, and this may be due to specular total reflection from the ‘tail’ of the E- region. Values of tIY in June were found to be much larger than in other months with O,, - 14, at 88 km, the

peak, and the winter months, June, July and August showed increased variability in comparison with the other months. The solid circles represent the mean of values he determined in the east-west and north-

south planes at particular times between November 1971 and March 1972. Agreement is very good below 95 km. Inspection of Fig. la clearly illustrates the variation between Fritts and Vincent’s results, and those of the other studies made at Adelaide. The major

differences occur below 80 km. We may obtain a simple estimate of the effective

antenna polar diagram in one plane by assuming a Gaussian form for the antenna beam. In this case, the power P received at an angle 0 relative to that received

from the vertical, and hence the effective antenna polar diagram, will be given by

P = expj - (sin O/sin Q,Y)’ 1

~exp(-(sinti-sin0,)2/(sin0,)2}, (1)

where 0, is the actual beam width, and the other terms have previously been defined. It can be shown that the effective beam pointing angle is that at which the most power is returned (see, e.g., WHITEHEAD et al., 1983) and so 0, may be obtained from the maximum of (1) as

0, = arcsin{ sin 0, sin* 8, /(sin2 0, + sin’ O,, )} . (2)

Upper middle atmosphere winds

Alt/km

119

5 Wes %E ldeg

Fig. la (left). The mean angular spread (0,) from the zenith of backscattered radiation at 2MHz measured at Adelaide in a number of studies, The solid line refers to LINDNER’S (1975b) mean values for May- November 1971, and the solid circles to mean values he measured between November 1971 and March 1972. The other symbols refer to GOLLY and ROSITER (1971) (open diamond), HOCKING (1979) (open triangles), FRITTS and VINCENT (1987) (open circles), and the present study (crosses). Points that are not

linked by a line should be given equal weighting. Fig. lb (right). The effective beam pointing angle (0,) calculated using some of the values of H, for an

apparent beam pointing angle (0,) of 11.6”.

Figure lb shows the effective beam pointing angle calculated by substituting Lindner’s mean results and the known beam width into (2) for an apparent tilt

angle of 11.6’. Inspection of this diagram suggests that if LINDNER’S (1975b) mean results are typical, there will be substantial errors in the measurement of

wind velocity over the entire height range of 60- IOOkm at Buckland Park if an off-zenith angle of 1 I .6’ is assumed. The same is true for the other results

shown. Even though (1) and (2) do not take into account the fact that the antenna beam is circular in cross section, or that the radar has a finite pulse length,

this simple approach appears to be quite accurate for a simple angular dependence such as that described above (e.g. HOCKING et al., 1986). However, HAUG and PETERSON (1970) and VINCENT and BELROSE

(1978) have both described data that required a scattering distribution that maximized away from the zenith. Their results refer to short lengths of data

and it should be recognized that the correction for the aspect sensitivity using (1) and (2) is true in an average sense only.

One other point should also be noted in connexion with this effect. If the beam half-width is larger than the off-zenith angle, the effective beam angle may actually be vertical or very near vertical. For instance, with a beam pointed at an apparent angle of 3” from the

zenith at Adelaide, and with 8, = 3’, which is appro- priate for heights below about 80 km according to Lindner, the effective beam angle 0, will be about 0.7‘

In this case it may not be possible to obtain a measure of either the horizontal or vertical wind components.

3. EQUIPMENT AND BASIC DATA ANALYSIS

Two normally independent radars were used with

a common transmitter to obtain the November 1980 measurements. A general description of the Buckland

Park aerial array has been given by BRICCS et al. (1969), and the facility when operated as a Doppler radar has been described by REID and VINCENT (1987a). Basic details relevant to the present study may be found in the latter work. For the November

1980 results reported here, the north-south and east- west aerial arrays were phased separately to produce

two independent broadside arrays. These were directed 11.6” off-vertical towards the north, and towards the west respectively. This system operated in its normal Doppler configuration.

The other radar was basically the same as that used for previous SA observations at the low latitude site of Townsville, Australia (VINCENT and BALL, 1981), and for subsequent measurements at the high latitude

120 1. M.

site of Mawson Base, Antarctica (MACLEOD and VIN- CbXT, 1985) but only the receiving portion was used. The Buckland Park transmitter was operated by both systems in a time multiplexing scheme, so that it was controlled alternatively for a total of 12 min every 20, first by the Doppler equipment for 6 min, and then by the SA equipment for 6min. The portabIe SA radar normally operates at a frequency of 1.94 MHz, but time limitations prevented its aerials being returned to the transmitter frequency (1.98 MHz), and only the EW element of the normally crossed dipole receiving aerials was erected. In addition, the receiving aerial spacing was 183 m on side, compared with the 165 m usually used. These limitations reduced the height range over which usable wind values are normally obtained with this system, as we shall see below.

During the 6 min each system controlled the transmitter, three 102.4s records of complex amplitudes were obtained at each height, in two independent channels for the Doppler equipment, and in three independent channels for the SA equipment. In each system, the real and imaginary components of the backscattered signals were sampled simuhaneously every 0.05s, in ten range gates of 2 km, in each channel. Eight consecutive points from a given receiver and height gate were averaged, and so complex amplitudes were obtained every 0.4s at each receiver and height. Records were of 102.4 s duration and separated by 17.6 s, so that one record could be obtained every 2 min at each height in each channel. Apart from the number of aerials and channels used, the Doppler and SA receiving systems were essentially identical. Phase coherent SA radars can be used in a Doppler (or interferometer) mode as we shall see below, and the essential difference between the two techniques involves the antenna array dimensions and the analysis of the data to recover the horizontal velocities. A tutorial discussion relating to the similarity of the techniques is given by BRIGGS (1980) and for discussions of their relative merits see R&I-TC;ER (1981).

The Doppler system records were processed off-line using an autocorrelation analysis in a manner similar to that described by W~K~MAN and GUILLEN (1974) to obtain the radial velocity. Records with low signal- to-noise ratios, or for which the phase of the autocorrelation function was not signi~cant were rejected. This analysis was identical to that applied by VINCENT

and REID (1983), REID (1984), REID and VINCENT (1987a. b), and FRITTS and VINCENT (1987). The SA system records were analyzed off-line using the so called full correlation analysis (FCA), as described in VINCENT and BALL (1981) and VINCENT (1984b). More general discussions of the method are given

REID

in BRIGGS (1984) and FRASER (1984) and interested readers are directed there.

It should be strongly emphasized here that the one essential difference between the SA and Doppler radars used in this study concerns the receiving arrays. The receiving arrays for the SA radar consisted of three half-wave inverted V dipoles. (That is, they were supported about 10 m above the ground at their centers, and about 1 m above the ground at their ends.) That for the Doppler radar consisted of 178 half-wave dipoles. The resulting lower signal-to-noise ratios for the SA radar should be borne in mind when data acceptance rates and the data quality are compared with those of the Doppler radar.

4. HORIZONTAL VELOCITY COMPONENTS

4.1. Noaemher I980 results

4.1.1. Velocities. A total of six days of SA and Doppler observations of wind velocities were obtained during 21-27 November 1980, and the acceptance rates of individual 2 min SA dete~inations of velocity are shown in Fig. 2. They are rather low, and heights of 80, 82, 96 and 98 km have less than a 20% acceptance rate. These heights have been excluded from further detailed analysis. These rates are considerably lower than those normally obtained by the complete portable system, which are comparable to those obtained when the Buckland Park facility is operated in a SA mode. These typically provide a 20-60% acceptance rate per hour between 80-98 km, with an overall acceptance rate of about 30-50% for heights

SA Acceptance Rates Ah/ km-

2l-2? November 1980

94 t 92

90 1

88 86 I' 84

82

80 -I

%t-ce$ % Acceptance

Fig. 2. The individual 102.4s data acceptance rates for the SA radar for November 1980. These values are somewhat lower than those normally obtained using this radar in its

normal configuration for reasons discussed in the text.

Upper middle atmosphere winds 121

Table 1. Cross correlation values for SA and Doppler wind components for the four height ranges for which more than 100 of the possible

144 h of SA data contained values

Ah. -- --

86 88 90 92

Zonal Merid.

0.66 0.78 0.68 0.82 0.66 0.83 0.51 0.70

above about 78 km (BALL, 1981). During daylight hours echoes are generally available over a full 24 h at heights above about 78 km, and for periods ranging between 8-12 h at heights down to 60 km by day (VINCENT, 1984b). Similar rates are obtained at Saska- toon (GREGORY et al., 1982). Doppler system acceptance rates varied from 70% at 80 km to 95% at 90 km, values which are quite typical for Doppler studies at Adelaide (REID, 1984 ; and see Fig. 13).

Figure 3 shows individual data points from both techniques for a height of 88 km for a few hours of observations. This example was selected at random from the available data. Agreement between winds derived from each technique is good, although the Doppler results appear to be somewhat more variable. These time series are rather short. and the level of gravity wave activity unknown, but there appears to be little evidence of atypical variations in velocity between techniques. and this was in Pact found to be generally true.

However, because these particular SA acceptance rates are rather low. and because both SA and Dop- pler measurements may be subject to contamination from vertical wind fluctuations for periods less than about 1 h (ROYRVIK, 1983 ; REID, 1987), the best time resolution considered practical was 1 h. Figure 4 illus-

trates hourly mean values of the meridional and zonaf wind components for five heights, for the 25.-27 November. The Doppler values in this diagram have been analyzed assuming equivalent apparent and effective off-zenith angles of 11.6”. Inspection of Fig. 4 suggests that generally, when values differ, Doppler derived wind velocities are smaIler in magnitude than those obtained with the SA technique. They are also generally smoother, although low SA acceptance rates arc certainly contributing to the considerable noise in that time series. Nevertheless, general agreement is good, and the mean features are evident in both time series. Cross correlation of the time series for those heights with sufficient data to make the calculation meaningful indicates mean values of about 0.6 and 0.8 for the zonal and meridional components, respectively (see Table 1). Because the effective off-zenith angle varies with range. the heights calculated assuming an off-zenith angle of 11.6 will not be correct, and the comparison shown in Fig. 4 is not strictly valid. How- ever, all of the mean square Doppler velocities are less than the mean square SA velocities (see Table 2). In addition, the height calculated on the basis of Lind- ner’s results is within 1 km of the height calculated using 0, = 11.6” (see Table 3), and so as a first approximation, Fig. 4 may be accepted.

4.12. Power spmtra. To check for differences between the two methods in terms of frequency, power spectra of velocity were calculated for each height. The significant gaps in the SA data at heights below 86 km and above 92 km make these time series of hourly averaged values unsuitable for this type of analysis, and we will concentrate on the 86-92 km height range. A cubic splines interpolation procedure was applied to smooth over small gaps in the data, and to improve the reliability of the spectral estimates,

Fig. 3. Short section of Fig. 4 for 25 November for individual (102.4 s) Doppler {closed circles) and SA (open circles) determinations of velocity at a height of 88 km. Apart from a tendency for the Doppler velocities to be more variable than SA velocities, there is little evidence of atypical variation in velocity

between the two techniques. This is a representative example.

122 I. M. REID

92

90

8%

36

92

0 6 12 18 0 6 12 16 0 ' '*LT 25-11-30 26-11-30 wll-30

Fig. 4. Time series of hourly mean SA (solid line) and Doppler (dashed line) zonal (top) and meridional (bottom) wind velocities for five heights for 25-27 November 1980. Note that Doppler values tend to underestimate the SA values. Regular tidal variations are clearly evident in both time series, and gross features are in very good agreement. The larger variability in the SA time series is due to lower data acceptance rates, and this is largely due to the much smaller receiving array used. It should be noted that

approximately 60 times more half-wave dipoles were used with the Doppler system.

Table 2. Total mean square horizontal velocity p = iX + ? as measured using SA and Dop- pler radars in November 1980. An effective off-

zenith angle of 1 I .6” has been assumed

Ah. (km)

,7r (mL s 4)

-.-_- - .-.- -.

SA Doppler

84 I268 259 86 1233 381 88 1154 521 90 1269 620 92 1264 728

the raw estimates from four adjacent frequency bands were averaged to produce one estimate. Meridional and zonal spectra were similar, and so to improve the estimate Further, they have been averaged together to form composite spectra. A similar procedure has previously been applied by BALL (1981), and VINCENT and BALL (1981). If the statistics of the motions are horizontally homogeneous, the average Doppler spectra thus calculated represent (for each frequency inter-

val A.0

(u’S+o’*)/2+w’~Cot~Of(U’U”-u’W’)COt0, (3)

where (22, ;;;‘, 7’) are the mean square zonal, me-


Table 3. The range, effective altitude, effective off-zenith angle (0,) and mean angular spread (0,) calculated using the November 1980 results, and calculated using the values obtained by LINDNER (1975b). The values of (0,) and (0,)

are shown in Fig. 1

November 1980 Calculated

Range Alt. (km) p) (“;

Alt. (km) (km) /“, ('j

86 85.6 5.2 4.9 85.1 7.6 1.5 88 87.5 6.4 6.0 86.9 8.6 9.2 90 89.3 7.4 1.2 88.8 9.2 10.7 92 91.1 8.1 8.3 90.8 9.4 11.3 94 92.9 8.8 9.7 93.0 8.9 9.9

ridional and vertical velocity components respectively, and (u’w’,u’w’) are the upward fluxes of zonal and

meridional momentum respectively (e.g. see REID,

1987). Since the quantity required is that given by the first

term in (3), there is some uncertainty in these spectra.

The importance of the second two terms in (3) increases with increasing frequency, but depends upon the signs of the covariance terms as to whether the

spectra are raised or lowered in a particular frequency interval. For periods down to about an hour,

, 7 d- - u’- >> d2 - 1 u’u”I - Iv’w’ 1 are reasonable as- sumptions. Typical values of u” and r’- in the 80-

90km height range at Adelaide are about 190 and 240m’s ~’ respectively for the l-8 h period range (VINCENT and FRITTS. 1987). Typical values of w” at 8.5 km in the 8 min to 8 h period range are about l- 6m’s-’ (REID, 1984), and typical values of u’u.’ are l-5 rn’sm2 (REID and VINCENT, 1987a; FRITTS and

VINCENT, 1987). Spectra of w” tend to be relatively flat, but [U’W 1 and 1 c’w’l maximize for periods less

than about 1 h, with a contribution of about 70% (REID, 1986 ; REID and VINCENT, 1987a; FRITTS and

VINCENT, 1987). Because of the cot’ 0 dependence of the M.‘- term, and because the covariance terms are signed quantities and not important for periods great- er than 1 h, the second term is more likely to be an important source of error than the last term for the November 1980 spectra.

We have already noted that zonal and meridional Doppler spectra are quite similar and this is particularly so for periods in the 2-S h range. This does suggest that the covariance terms, which are most important for periods less than about l-2 h, are not likely to be significant for these particular spectra. This is clearly demonstrated by inspection of Fig. 5a, which shows the zonal and meridional Doppler spectra for 88 km. However, there is a systematic

difference between the meridional (I”‘,) and zonal ( V’2,) Doppler mean square radial velocities, with a

meanratioof V’2,/V’2,0ver 84-92 kmof 1.1.5+0.07.

The major contribution to this difference occurs for

periods longer than about 5 h, with the 2-5 h sections of the EW and NS spectra exhibiting little variation. The difference between the components appears to be related to the isotropy of the wave field, and the ratio is in excellent agreement with that found by VINCENT

and FRITTS (1987) for p/p for the 8-24 h period ranges from monthly averaged SA mean square velocities in November 1983 and 1984 at Adelaide. The ratio of p/u’? for the 1980 SA results is 0.93 k 0.13,

the variation between SA and Doppler results most likely being due to the higher noise levels in the SA

time series. By comparing zonal spectra calculated with and

without the vertical mean square and covariance terms included for November 1981 (see REID, 1987), we estimate the RMS error in (I_/‘)“” to be about

1 rns-’ when calculated over the entire frequency range. A similar value would apply to (c’-)“~. There

was no significant difference in spectral slope or general form. Only three days of data were obtained in November 1981. and only the zonal component was

obtained, but agreement with the November 1980 data is good. Consequently, it appears that November

1980 Doppler method spectra are quite typical of the horizontal fluctuation in velocity in each frequency

range as measured with the Doppler technique. and reasonable estimates of (u” + v”)/2.

The spectra for 86 km are shown in Fig. 5b. Agree-

ment in form is good, but in a given frequency interval, the Doppler method spectrum has a value typically less than half that of the SA spectrum. Even so, both spectra show typical behaviour for this type of power spectrum, in that power decreases on average with increasing frequency, from the inertial period (20.9 h

at Adelaide), to the frequency limit imposed by the sampling interval (about 2 h). Such spectra may be approximated by a power law relationship of the form S(S) = S,f ~‘. where S, and k are constants and ,f is the frequency. The lines of best fit resulting from such a least squares power law fit to the seasonally averaged results for Adelaide and Townsville for 86km (VINCENT, 1984a), and for summer results obtained at Poker Flat for the same height using the Poker Flat VHF Doppler radar (BALSLEY and CARTER, 1982) are also shown in Fig. 5b. The SA results for this height are clearly in better agreement with Vincent’s seasonally averaged results, and with the Doppler results from Poker Flat.

The spectra for 88 km are shown in Fig. 5c, and they are very similar to those for 86 km. To establish

124 I. M. REID

I 1 I r ’ 21-21 November 1580

M&i& ..-..

_Pder Fiat-.- Towmilk? ---

I 1 I , I I

lo5 10% f/Hz

Fig. .5a (top left). The power spectra for the meridional (solid line) and zonal (broken line) components of the velocity measured using the Doppler technique at 88 km.

Fig. 5b (top right). The power spectra for SA and Doppler wind values for X6 km. Solid straight lines indicate lines of best frt of the form S(f) = S,f-*, with S, and k constants, to the 2-8 h period range. The other straight lines indicate similar tits made to spectra at 86 from Adelaide, Poker Flat and Townsville. The SA spectrum is in good agreement with these values, and appears to provide a better estimate of the

correct value, even though data acceptance rates are marginal. See text for details. Fig. 5c (bottom left). As for Fig. 5b but for 88 km. Also shown is the SA spectrum for November 1978, and the line of best tit to the mean spectrum for 19X1 at Saskatoon for the same height. As for results

shown in Fig. 5b. the Doppler method spectrum appears to underestimate the correct value. Fig. 5d (bottom right). As for Fig. 5a but for 90 km.

that the power spectra obtained using the portable SA SA spectra at this height is good, although the equipment are typical of those normally obtained at November 1980 spectrum tends to be somewhat lower Buckland Park for data lengths of l-2 weeks, the SA over most of the frequency range. This difference can power spectrum for November 1978 is also shown be attributed to differences in the total data lengths, (VINCENT and BALL. 19X1). Agreement between the and to the separation in time of the observations, but


21-Z’ Nom-her 1983

Spectral Index Z-8h

Fig. 6. The spectral index k for the 2-8 h period range obtained using the power law fit discussed in the text to the SA and Doppler method spectra. There is no significant difference between values of k as measured with the different techniques. The mean value of k for these results is 1.6. The crosses indicate the effective height of the Doppler values

calculated using the results in Table 3.

it is clear that the November 1980 SA data is typical

of that obtained at Adelaide at this time of year. It is also in better agreement with the mean spectrum for 1981 at Saskatoon at 88 km (MEEK et al., 1985), and the line of best fit for l-8 h for that site is also shown

in Fig. 5c. The spectra for 90 km (Fig. 5d) are consistent with those for 86 and 88 km, with the Doppler

method spectrum again underestimating the SA spectrum.

The better agreement of the SA spectra at each height with the spectra from Adelaide, Townsville,

Saskatoon and Poker Flat suggests that the Doppler

spectrum is an underestimate of the correct value in each case. The SA spectra are also in better agreement with the mean of summer and winter mesospheric spectra measured at Andoya, Norway, by CZECHOW-

SKY and ROSTER (1985), but this comparison is less satisfactory because of the height averaging applied by these authors. The spectral slope (k) for each of

the spectra from 86 to 92 km is shown in Fig. 6. Agree- ment is very good, indicating a general reduction in Doppler values rather than a reduction of particular frequency bands. The mean slope is - 1.6, in good agreement with values found in the studies noted above.

Agreement between SA and Doppler method spectra tends to improve with height, as inspection of Figs. 5bd indicates, and the mean square velocity for each spectrum for both components evaluated over the

entire frequency range is shown in Table 2. The value

for SA observations at 84 km has been estimated from only those days with sufficient data, and so the uncer-

tainty in this value is likely to be higher than in the

other values. Inspection of this table indicates that SA values are essentially constant with height, while Doppler values increase with increasing height. This is an important difference, because the wave energy density pV” (where p is the neutral density and

V” = u”+r:‘*) should remain constant for conservative wave motion.

Since p decreases as exp[ -z/H], where H is the

density scale height, V’* should grow as exp[z/H] for conservative wave motion, and the Doppler values would in fact be consistent with this kind of variation below 92 km. In contrast, the SA values suggest that wave energy is being lost. However, the variation in

Doppler values is consistent with the results shown in Fig. lb, and it would appear that this variation is due to that in eE with height.

If the effective off-zenith angle varies significantly

with height, then the height to which the Doppler measurements refer is uncertain. However, because

the mean square SA velocities found here are essentially constant with height, an estimate of BE may be

obtained for each Doppler range by comparing the corresponding mean square velocity with the mean SA value in the 8494 km height range. The actual height can then be calculated. This has been done, and Table 3 shows the range, equivalent height, mean

angular spread, and off-zenith angle for the Doppler values. The values of 0, and aE are also shown in Figs. la and lb, respectively. Inspection of this diagram indicates a variation in height similar to those corresponding to LINDNER’S (1975b) mean results,

although the values for November 1980 are generally

1-3” less. They are I-2” less than his results for November 1971. The considerable noise in the SA time series suggests that the values of 0, derived for November 1980 are likely to be underestimated, and consequently the agreement seems reasonable.

4.2. Other results

REID and VINCENT (1987a, b) have presented a se-

ries of measurements of momentum flux and horizontal scales associated with short period mesospheric internal gravity waves obtained using the Buckland Park facility as a Doppler radar. These measurements are superior to those of November 1980, because three and four beam configurations were used, and better estimates of horizontal velocity spectra and mean winds are possible (see REID, 1987), and because data acquisition rates were higher. For many of these

126

a I , I

6- 9 November 1981, B6km

105-

I- f/ Hz

6-9 Fig. 7. The zonal and vertical power spectra for November 1981. The broken line renresents the seasonal

I. M

average value of zonal (or meridional) bower spectral density at Adelaide. The solid lines represent lines of best tit to the spectra. The centre spectrum indicates the result that is obtained by assuming an off-zenith angle of 11.6”. while solid represents that calculated assuming an angle of 7.0. The spectrum calculated using the latter value is in better agreement with the average value of the power spectral density

for Adelaide.

measurement periods, SA winds were also measured either before or after the Doppler measurements to obtain an estimate of the correct background wind. In this Section we briefly consider some representative examples of these results.

4.2.1. Velocity spertru. In November 1981 observations were obtained with beams directed at 11.6” eastward and westward, and to the zenith. The power spectra for both the zonal and vertical wind components for a range of 86 km are shown in Fig. 7. To calculate the true zonal spectrum, the effective beam angle for 85 km was taken from Fig. I b and used to rescale the mean power spectral density of the eastward and westward radiai velocities, and the vertical spectral density was then removed. This provides an exact measure of u’” (see REID, 1987). Also shown in Fig. 7 is the ‘zonal’ spectrum that would have been obtained if the effective beam angle had not been used, and the line of best fit for 86 km for the seasonally averaged SA result at Adelaide (VINCENT. 1984a). Inspection of Fig. 7 indicates that the resealed spectrum of U” is in good agreement with the seasonally

REID

I I, , 1, 1

Id lC!-i0 May 1962, 86km

1

Fig. 8. The zonal power spectrum for 19-20 May 1982 corrected (solid line) and uncorrected (broken line) for variation between effective and apparent off-zenith angles. As for Fig. 7, the corrected spectrum provides a better measure of the

seasonally averaged value.

averaged result, while the unscaled results are somewhat lower. The few lowest frequency points of the spectra may be uncertain, because the time series were filtered to remove periods longer than 8 h, but the remaining points should give a good measure, and it appears that the effective beam angle for 85 km from Fig. 1 b is a reasonable estimate. Figure 8 illustrates a similar spectrum for May 1982. It was calculated as for that for November 198 1, but we have also included the lower frequency portion. It is clear that the resealed spectrum is a much better estimate of the seasonal average. These results are typical of all others from measurement periods described by REID and VINCENT ( 1987a, b).

Recent studies have suggested a seasonal variation in the mean square horizontal velocity for particular period ranges (or equivalently, in the power spectral density) with minimum values near equinox (MEEK et

al., 1985; VIWENT and FRITTS, 1987). This is not likely to be the reason for the difference between the seasonally averaged result of VINCENT (1984a), and those for the unscaled spectra of November 1980, November 1981 and May 1982 however, because measurements of 0” and u’~ derived from various beam configurations in each observational period are smaller than the seasonally averaged SA value, and


A&/km r

0 IO 20 M D/ms'

40 -10 -5 0 Vmd

5

Fig, 9a (left). The mean zonal wind component for the 30 June-16 July 1982 uncorrected for the aspect sensitivity of the backscattering irregularities (crosses), corrected according to Fig. I (closed circles), and corrected according to the results of FRETS and VINCENT (1987) (open triangles). Mean wind values for

July derived from SA measurements for 197%1983 are also shown (open circles). Fig. 9b (right). As for Fig. 9a but for meridional components.

127

intercomparison of the same quantities measured in each month with SA results presented in BALL (1981) for the same months (but different years) indicates that Doppler measurements of the horizontal component of kinetic energy are always too small if an off-zenith angle of 11.6” is assumed.

4.2.2. Mean horiz~~t~~ winds. Inter~om~rison of the mean winds measured in adjacent periods of a few days is complicated by the presence of longer period variations in the calculated mean wind values. Some measure of the validity of the measured winds can be obtained by comparing them with the monthly values for Adelaide (such as those tabled in MANSON et al., 1985), but these mean values are often associated with large standard deviations, and so might not be validly applied to a particular period of observation. Conse- quently, such results cannot validly be used for any detailed comparison or calculation of effective off- zenith angles, but they do usefully illustrate the need to correct for the effective off-zenith angle.

Figure 9 shows the mean height profiles of zonal and meridional velocity for 16 days of observation in winter 1982, calculated assuming a beam pointing angle of 11.6” (crosses), and calculated using the results 0, shown in Fig. 1 b (closed circles). Also shown are the height profiles obtained using the SA technique over the years 1978-1983 at Adelaide (open circles). Inspection of this diagram indicates that the correction for the aspect sensitivity of the scatters significantly improves the agreement between the wind profiles derived from the SA and Doppler techniques. but that the corrected values tend to be less than

AR/km lOO* I 1 1

'P 2x35 April 1982 -

- :, l . x

-10 0 -1 10 20 30 40 li/ms

Fig. 10. The mean zonal wind component for the 21-26 April 1982 uncorrected for the aspect sensitivity of the backscattering irregularities (crosses), and corrected according to the values of 8, from Fig. Ib (closed circles). Mean wind values for the 28-30 April 1982 derived from SA measurements are also shown (open circles), as is the mean SA wind

profile for the I-30 April 1984 (triangles).

the long term average value. The correction we have applied would appear to overestimate QE in the 86- 92 km height range, and for June in 1984 at Adelaide, FRITT~ and VINCENT (1987) have estimated a slightly lower value. However, application of their results makes little difference to the agreement between the height profiles (open triangles).

Figure 10 shows the mean height profile of zonal

128 I. M

velocity measured over five days in April 1982, calculated assuming a beam pointing angle of 1 t.6” (crosses>, and calculated using the results shown in Fig. 1 b (closed circles). Also shown are the height profiles obtained using the SA technique for 28-30 Aprii 1982 (open circies), and the mean zonal wind for l-30 April 1982 (open circles), and the mean zonal wind for l-30 April 1984 (triangles), the best mean values currently available in the literature for this month at Adelaide (see VINCENT and FRITTS, 1987). This diagram indicates that the Doppler wind values calculated assul~ing an ok-zenith angle of 11.6” underestilnate the mean SA height profiles. and agreement is again significantly improved when the aspect sensitivity is taken into account. The corrected Dop- pler profile agrees very well with the monthly mean value. but underestimates that for the 2830 April.

5. MEAN VERTICAL WINDS

Apart from its effect on off-vertical beams, there is one other interesting consequence of enhanced backscatter from the zenith, namely that for wide vertically directed beams, such as those used in the SA experiment, the effective antenna polar diagram is determined by the backscatter polar diagram, and may be quite narrow. Consequently, it may be possible to obtain an estimate of the mean vertical velocity using phase coherent SA equipment, such as that used at MF and VHF at Adelaide, and previously with the SOUSY MST radar at VHF, simply by caI~ulatin~ the mean Doppler shift of the backscatter Doppler spectra at any of the three receiving sites. This should be especially so for mesospheric studies below heights ofabout 75-80 km (see Fig. la). Even so, theincidence angle of the returned signal should be measured to correct for off-vertical veIocity components, and R~TTGBR (I 981 b), R~~TTGER and IERKIC (198S), and V~WENT et ul, (1987) have applied this interferometric technique to data obtained with standard phase coherent SA equipment at VHF. None of these authors do this on a routine basis, but such corrections are routinely made in the Meteor Radar technique (e.g. ELFORD and CRAIG, 19SO), and routine application would make better use ofthe phase information which is not exploited fully in the SA experiment at present. Our intention here however, is only to provide a quick look at the potential of such measurements at MF, and we do not correct for off-zenith returns. Measure- ments of vertical velocity are difficult to establish as actually representing the motion of the atmosphere. and are subject to a number of uncertainties, but we can determine how close the quantities measured by

REID

Doppler and SA radars are. During 3-6 December 198 1, observations of radial

velocity were obtained using both wide (2 20”), and narrow ($_4.5”) vertically directed beams. The wide beams correspond to the three groups of four aerials normally used at Buckland Park to obtain SA wind velocities {e.g. STU~BS, 19731, and the narrow to an entire broadside array of 78 half-wave dipoles. These four channels were preprocessed in an identical fashion. and written to magnetic tape. The three wide beam channels were processed off-line as for the normal SA experiment to obtain horizontal wind velocities, and as Doppler channels to obtain an estimate of vertical wind velocity.

Figure lla illustrates the hourly averaged radial velocities measured in the 68-78 height range for 4 December 198 I. Data were not recorded between 1800 and 0500 LST below 80 km, and observations were taken at a rate of I in 8 min, which is consistent with typical run rates for SA observations currently made at Buckland Park. Data from the three SA receiving beams were averaged, and apart from this, all data were processed in exactly the same way. Below 74 km, agreement is good, but as expected at the upper height ranges the wide beam velocities are rather more noisy, and general agreement is only fair. Figure 1 I b illustrates the time series for 84-94 km for 6-7 December. The run rate for these observations is 1 in 4 min. Agreement is again variable, but the gross features arc reasonably consistent, and it is clear that both beamwidths are measuring the same thing.

The consistency of these results is quite surprising and indicates that estimates of mean (-day) vertical winds could be obtained at Buckland Park at MF with the basic SA configuration. However, the variable agreement evident in Figs. 11 a and 11 b indicates that correction for off-vertical returns should be applied. As noted by VINCENT’ et a(. (1987). some additional care may also be necessary in inferring vertical velocities, because the transmitting and receiving aerials are usually separated in the SA experiment, and because of the resulting geometry, signals will be scattered at small angles to be vertical. Contamination of the vertical component may be significant for the VHF SA experiment at low altitudes where the effect is most severe.

6. DlSCUSSION

In the preceding Sections it was assumed that the SA rather than the Doppler horizontal velocities as measured at Buckland Park were closer to the correct values. This seems reasonable because of the agree-


4/X?JW 6112181 7/12181

Fig. I la (left). The hourly mean radial velocity measured in both wide (t-20”) (solid line) and narrow (f4.5”) (broken line) vertically directed Doppler beams for 3 December 1981, Below 74 km agreement is

fair, a result consistent with the values of 0, shown in Fig. la. Fig. 11 b (right). As for Fig. 1 la but for 84-94 km for the 6-7 December 1981. The vertical scale represents 1 m s-’ per division. Agreement is rather variable, but radial velocities measured in both wide and narrow

beams show similar variations.

ment between November 1980 SA results, and the

similar, though seasonally averaged, results of BALSLEY and CARTER (1982), VINCENT (1984a), MEEK

et al. (1985), and CZECHOWSKY and ROSTER (1985).

The validity of this kind of argument depends on the geographical variation of the wind field, and upon the notion of some kind of ‘universality’ in the power

spectra (e.g. VAN ZANDT, 1982), and is true only in a statistical sense. There are obviously uncertainties in measurements obtained with both techniques. Uncer- tainties in the SA derived winds obtained in November 1980 arise because of the relatively low data accep-

tance rates, and the corresponding noisy and inter- mittent time series, while uncertainties in the Doppler

derived winds arise because the vertical wind com-

ponent has not been removed, and because the effective beam off-zenith angle depends upon the aspect sensitivity of the backscatter.

However, because we can improve the agreement between Doppler observations for various months and the seasonally averaged mean and mean square velocities measured at Adelaide through estimates of eE based on measurements of 0, made with a com- pletely different technique, there is compelling evidence that the effective beam angle is less than the apparent beam angle, and that the measurements of tIY made by LINDNER (1975b) give a reasonable mea-

sure of this quantity. However, it must be stressed

130 I. M. REID

that this correction is only valid for observations taken over a suitably long period of time, and is then only correct in a statistical sense. Characteristics of the backscattering regions certainly vary considerably throughout the year at VHF (CZECHOWSKY et al.,

1981) and we have already noted that a recent study by FRITTS and VINCENT (1987) in June 1984 at Adelaide found a different variation of 0, with height to that calculated from LINDNER’S (1975b) mean results, and from the November 1980 results (see Fig. lb).

Many comparisons between SA derived winds and winds derived from other methods have been reported for mesospheric observations at a variety of scales at MF. These include comparison of high time resolution (-4min) SA wind profiles with those obtained from dropsondes and falling spheres in the 60-90 km height range (VINCENT et nf., 1977), tidal components and mean winds using both meteor and SA techniques (STUBBS, 1973; STUBBS and VINCENT, 1973), and rocketsonde and SA mean winds obtained over many years (MANSON and MEEK, 1985). Agreement between the various methods is good.

The Doppler technique has also been compared with many other methods, and when narrow beamwidths are used, agreement between the various methods is also good. When wider beamwidths, or b~amwidths which are wide when compared to the off- zenith angle are used, agreement is little more variable. Riittger and Czechowsky found that when the SOUSY Radar was used in a Doppler radar mode for tropospheric wind observations, deviations of up to 10m s- ’ occurred in the horizontal velocity obtained from off-zenith angles of 3.5” and 7’ at the radar observed tropopause. In this region, the contribution of reflection to backscatter is quite large, so that the backscatter polar diagram will be relatively narrow about the zenith. Since the one way radar beam width used in their work was about 5, R~~TTGER and CZECHOWSKY (1980) suggested that the variation in the calculated ho~zontal velocity with zenith angle was due to the effective beam direction being somewhat less than the normal beam pointing direction.

A comparison of MF SA and VHF Doppler derived mesospheric winds by RUGGERIO and BOWHILL (1982), made with a (Doppler) half power beamwidth of about 4.0” (ALLMAN and BOWHILL, 1976), and an apparent off-zenith angle of 1.5” indicated considerable variability in agreement with height. As noted in Section 2, when the array beamwidth is larger than the off-zenith angle, there may be considerable contamination of Doppler spectra by scatter from the zenith. The data set of Ruggerio and Bowhill is rather limited, and shows a rather large spread, so that it is

hard to assess the reliability of the data they present. However, they suggest that the best agreement is found at heights where the scattered power is highest, and at these heights, the Doppler results generally underestimate SA values, with Doppler derived wind magnitudes being typically less than half of those for SA wind. Later work using the same (Doppler) radar suggests that estimates of horizontal velocities obtained using that facility are usually underestimated (ROYRVIK and GOSS, 1983).

Even though Doppler derived wind velocities at Adelaide are subject to uncertainty because of the aspect sensitivity of the backscattering irregularities, the higher gain of the receiving array, and the smaller volumes sampled, ensure excellent continuity in time and height of the measured radial velocities. Figure I2 illustrates hourly averaged height profiles of zonal and meridional Doppler velocities for the 6 days of November 1980 observations. These values have not been corrected for the aspect sensitivity. Even so, various features, but particularly the tidal variations, are clearly evident, and in terms of height and time coverage, these observations are superior not only to typical SA results, but to typical mesospheric results obtained with VHF Doppler radar, including those from the most powerful currently available, the SOIJSY, Poker Flat and MU radars (e.g. BAL~LEY rt al., 1983 ; CZECHOWSKY and ROSTER, 1985 ; SATO ef al., 198s).

Good data acceptance rates are also obtained below 80 km at Adelaide. The data acceptance rates for the off-vertical beam directions for November 1981 are shown in Fig. 13. Records were initiated every 2 min in the 7&100 km height range. Rates steadily increase from 21% at 74 km to a maximum of 96% at PO km. Below about 80 km, fewer records are available at night because of the reduction in ionization. The con- centration of accepted records in the daylight hours means that good estimates of velocity are possible at least down to 70 km during the day. Acceptance rates do vary, and as an example, results for May 1981 below 80 km are also shown in Fig. 13, but the available data are inadequate to thoroughly investigate these kinds of variations. The data acceptance rates in general are much higher than typical SA acceptance rates (see Section 4.1). and exceptionally higher than typical VHF-MST radar rates. Work in progress suggests that the acceptance rates in the 70-80 km height range shown in Fig. I3 can be significantly improved by more efficient analysis of the Doppler spectra.

The potential of MF/HF Doppler radars to investigate the upper middle atmosphere is underscored by the fact that the Buckland Park facility transmits using a half-power half-beamwidth of 40’, and for the measurements presented here, at a peak power of


ZONAL HOURLY AVER/GE HEIGHT PROFILES

131

MERIDIONAL HOURLY AVERAGE HEIGHT PROFILES

96

90

Fig. 12. Hourly average height profiles of zonal and meridional Doppler velocity for the 6 days of observation in November 1980. Individual height profiles are shifted by IO m SC’, so that on the horizontal axis, an interval of 6 h corresponds to 6Oms-‘. These profiles have been obtained assuming an off-zenith angle of 11.6”, but even without a correction for the aspect sensitivity, various features, particularly the

tidal variations, are clearly evident.

132 I. M.

86

84

82 I 80

78 ___,___’ 76

74

72 Ii I I ‘ , , I

50 100

% Acceptance

Fig. 13. The acceptance rates of individual 2min velocity determinations for 69 November I98 I (72-94 km) and I I- 14 May 1981 (72278 km) for off-vertical Doppler beams. With more efficient analysis of the individual Doppler spectra, the acceptance rates below 80 km could be con-

siderably increased.

about 25 kW, and receives on a half-power half-beamwidth of4.5’. Transmission and reception on the same array, and operation at the nominal peak power of

50 kW would considerably increase the proportion of usable returns from below 80 km. For vertically directed beams we have already seen that reasonable results can be obtained down to 68 km during daylight

hours (Fig. 1 la). With the addition of a vertical beam to the configuration used in November 1980, it would be possible in principle to calculate 0, and hence B,,

using the procedure followed by HOCKING et al.

(1986). This would perhaps be the optimum im- plementation of the Buckland Park MF array for wind measurements. However, it should be noted once

more that optimally configured SA radars provide much better data acceptance rates and data quality than that obtained using the portable SA radar in

November 1980. As we have noted, routine operation of the BP facility as a SA radar utilizes 12 aerials, and as a Doppler radar, 178 aerials. This factor (- 15) is not reflected in the relative quality of the data, and in addition the correction for the aspect sensitivity must be applied to the Doppler data.

7. SUMMARY AND CONCLUSION

Preliminary comparisons of MF SA and Doppler radar derived wind velocities have been presented.

REID

For relatively wide Doppler beams directed off-zenith,

it is essential that the aspect sensitivity of the backscattering irregularities is taken into account, other-

wise horizontal velocities are underestimated. When corrected for this effect, Doppler estimates of horizontal velocity are in good agreement with SA estimates. Frequency power spectra of horizontal velocity fluctuations for both techniques show excellent agreement in form, although the Doppler derived power spectra are typically half the magnitude of those for the SA values unless the aspect sensitivity is taken into account. The mean slope in the 2-8 h interval for the power spectra is - 1.6, and SA and corrected Doppler

power spectra are in good agreement with those from other widely spaced locations. Vertical velocities inferred from a standard phase coherent MF SA radar are consistent with those measured using a MF Dop- pler radar, although variability in agreement suggests

that the SA equipment should be operated in an interferometric mode. The results as a whole suggest that SA and Doppler techniques measure the same par- ameters at least for averages of an hour or longer, but that each has its own advantages. MF SA radars can

utilize extremely simple antenna arrays, and appear to measure horizontal velocities directly, while MF

Doppler radars provide extremely good height and

time coverage, and can sample small spatially separated volumes. It is noteworthy that the SA receiving

array used for the November 1980 comparison was rather inferior to that normally used. and the SA radar as a whole was not optimally configured. Never-

theless, reasonable results were obtained. As a final point, it should be emphasized that the

newest results presented here are from July 1982, and the oldest from November 1980. Considerable improvement in instrumentation suggests that it

should be possible to conduct a more detailed inves- tigation of SA and Doppler techniques using an optimally configured SA system now. It is to be hoped that this will be attempted.

Acknowledge~nmts-This work was carried out using the facilities of the Physics Department, University of Adelaide, Australia, whilst the author was in receipt of an Australian Commonwealth Postgraduate Research Award. Many useful discussions with Dr R. A. VINCENT of that institution are gratefully acknowledged, as is his and ROD MACLEOD’S help in preparing the equipment for the November 1980 comparison. Useful reviews by ALAN MAN~QN and J~~RGEN R~~TTGER are also gratefully acknowledged. Special thanks are due to HOLLY WALKER who drew the diagrams, and to SAM WALKER who assisted in surveying the large array site.


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133

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BRIGGS B. H., ELFORD W. G., FELGATE D. G. GOLLEY M. G., RO.CZ.ITER D. E. and SMITH J. W.

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FUKAO S. T., SATO T., HARPER R. M. and 1980 KATO S.

FRITTS D. C. and VINCENT R. A. GOLLEY M. G. and ROSSITER D. E. GREGORY J., MEEK C. E. and MAN~~N A. H. HAUG A. and PETERSON H. HOCKING W. K. HOCKING W. K. HOCKING W. K., ROOSTER R. and CZECHOWSKY P JONES K. L. LINDNER B. C. LINDNER B. C. MACLEOD R. and VINCENT R. A. MANSON A. H. and MEEK C. E. MANSON A. H., MEEK C. E., MA~SEBEUF M.,

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SATO T., TSUDA T., KATO S., MORIMOTO S.. 1985 FUKAO S. and KIMIJRA I.

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134 I. M. REID

VINCENT R. A. and BELROSE J. S. VINCENT R. A. and FRITTS D. C. VINCENT R. A. and REID I. M. VINCENT R. A., STUBBS T. J., PEARSON P. H. 0..

LLOYD K. H. and Low C. H.

1978 1987 1983 1971

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WHITEHEAD J. D., FROM W. R.. JONES K. L. and MONRO P. E.

1987

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Rqference is also made to the,following unpublished material.

BALL S. M. 1981

&ID I. M. 1984

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Radar studies of atmospheric gravity waves, Ph.D. Thesis, University of Adelaide, Australia.

mf doppler and spaced antenna radar measurements of upper middle atmosphere winds

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