Winds and waves in the middle atmosphere at Saskatoon (52°N, 107°W), Collm (52°N, 15°E) and Badary (52°N, 105°E)

Winds data from three radar systems in the U.S.S.R. G.D.R. and Canada, which are well-spaced along the 52°N latitude circle, are used to illustrate longitudinal/regional variations in the dynamics of the upper middle atmosphere 80–97 km. Responses to the stratospheric warming of 1982/3 are noted at all three locations, but the zonal wind does not reverse at Badary, consistent with the flow there being eastward during all months of the year. Planetary wave period oscillations (2–30 days) are observed at all locations, and highly significant cross-spectral coherences exist between the three stations.     

Climatologies of semi-diurnal and diurnal tides in the middle atmosphere (70–110 km) at middle latitudes (40–55°)

The radars utilized are meteor (2), medium-frequency (2) and the new low-frequency (1) systems: analysis techniques have been 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 semi-diurnal tide is generally larger than the diurnal (10–30 m s⁻¹ vs. < 10 ms⁻¹), and displays less month to month variability. The semi-diurnal tide does show significant regular seasonal structure; wavelengths are generally small (⩽50 km) in winter, large in summer (≲ 100 km), and these states are separated by rapid equinoctial transitions. There is some evidence for less regularity toward 40°C. Coupling with mean winds is apparent. The diurnal tide has weaker seasonal variations; 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. Again the seasonal transitions are in phase with reversals of the zonal wind. Agreement with new numerical models is to be shown encouraging.     

Thermospheric and mesospheric temperatures during geomagnetic storms at 23°S

Night-time thermospheric temperatures, T63o, and mesospheric rotational temperatures, T(OH) and T(O₂), have been measured at Cachoeira Paulista (23°S, 45°W, 16°S dip latitude), located in both the equatorial ionospheric anomaly and the South Atlantic Geomagnetic Anomaly, with a Fabry-Perot interferometer and a multi-channel tilting filter-type photometer, respectively. The thermospheric temperatures are obtained from the Doppler line broadening of the OI 630.0 nm emission and the mesospheric rotational temperatures from the OH(9,4) and O₂A(0,1) band emissions. Measurements made during three geomagnetic storms showed that the nocturnal mean values of T₆₃₀ during the recovery phase of the storms were lower than those observed during quiet time and from model predictions. Also, the nocturnal mean value of the T₆₃₀ soon after the SSC event on 27 June 1992 was higher than the quiet time and model predictions. The observed mesospheric nocturnal mean rotational temperatures, T(O₂) and T(O₂), were unaffected by the storms. A comparison of the night-time observed temperatures T₆₃₀, T(OH) and T(O₂) with those calculated using the MSIS-86 model is also presented.     

Variations of mean winds and tides in the upper middle atmosphere over a solar cycle,Saskatoon, Canada, 52°N, 107°W

Saskatoon (52 N, 107 W) medium frequency (MF) radar data from 1979 to 1990 have been analyzed to investigate the solar activity effects on upper middle atmospheric winds and tidal amplitudes. The period of study covers two solar maxima and a solar minimum; the continuous data allow a systematic analysis of solar cycle dependence on mean winds and tides. The height region of 79–97 km sampled in the study shows an apparent but very weak dependence of mean winds and tidal amplitudes on solar activity variation. The observed features are fairly consistent with the early results reported by Sprenger and Schmindkr [(1969) J. atmos. terr. Phy. 31, 217). The mean zonal wind and the semidiurnal tidal amplitudes appear to exhibit positive and negative correlations with the solar activity, respectively; the statistical significances of these correlations are generally low. There is a biennial periodicity evident in the zonal wind oscillations but this docs not have a consistent phase relationship with the equatorial stratospheric wind oscillations (QBO). The meridional winds and the tidal amplitudes are characterized with different and quite irregular periods of oscillations (2–5 yr). The diurnal tidal variations over the solar cycle are small and irregular, although amplitudes are slightly larger during the solar minimum years.     

Winds oscillations (∼ 6h–6days) in the upper middle atmosphere at Monpazier (France, 45°N, 1°E) and Saskatoon (Canada, 52°N, 107°W) in 1979–1980

The medium frequency radar (∼ 2.2 MHz) at Saskatoon has been run continuously since 1978 and the Meteor Radar at Monpazier ran continuously for ∼ 10 day intervals in most months of 1979/1980. The radars are separated by ∼ 8000 km. Because of the excellent quality of the data, spectral and harmonic analyses have been completed from ∼ 70 to 100km and oscillations with periods of ∼ 6h–6days studied.There are substantial similarities in the mean zonal winds, both with regard to magnitudes and times of seasonal reversals; also in annual and semi-annual oscillations. In general, the semi-diurnal tide has similar amplitudes, phases and vertical wavelengths : there are consistent summer (long λ) and winter (short λ) characteristics, with rapid transitions between them. Differences between the timing of these transitions and in some of the mid-season tides are discussed. The diurnal tide is less regular and of smaller amplitude at both locations, often being too small to reliably characterize at Monpazier. However, seasonal variations between summer and winter months may be discerned.In addition to the 24 and 12 h tidal oscillations, which traditionally are studied in most detail, there is clear evidence for additional osculations near 6,8, ∼ 10 and ∼ 16 h and longer periods of ∼ 2 and ∼ 5 days. The amplitudes of these are often comparable or larger than the ‘dominant’ 24 and 12 h tides. The monthly and seasonal variations of these additional oscillations are studied, as a function of height, at the two locations. There is evidence for large scale (global) and small scale (local) disturbances in the wind field.     

Dynamics of the upper middle atmosphere (80–110 km) at Tromsø (70°N) and Saskatoon (52°N), June–December 1987, using the Tromsø and Saskatoon MF radars

A real-time-winds (RTW) system from Saskatoon operated with the Tromsø MF (partial reflection) radar system on a continuous basis in the period June–December 1987. This interval includes MAC/SINE and EPSILON. Profiles with 3-km resolution were obtained every 5 min—weak ionization and few geomagnetic disturbances limited the observations normally to 80–110 km. However, daily mean winds, diurnal and semidiurnal tidal characteristics (amplitudes, phases and wavelengths) and gravity wave characteristics (intensities, mean directions) are available throughout this interval. 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 these dynamical parameters from Saskatoon (52 N) are made : the zonal circulation was weaker at Troms0, tidal amplitudes smaller, and summer 12-h tidal wavelengths shorter ( ~ 80 km vs ~ 100 km). The fall transition for this tide occurred in September at Troms0, earlier than observed elsewhere.     

The characteristics of the mesospheric two-day wave as observed at Grahamstown (33.3°S, 26.5°E)

The characteristics of the quasi two-day wave, as observed in meteor wind data recorded at Grahamstown (33°19′S, 26°30′E) between April 1986 and April 1989, are described and discussed in the context of existing knowledge. As is typical, the wave amplitude has been largest during the summer months December–February with a maximum in late January, but this amplitude has differed markedly from year-to-year. The period and phase are found to be variable and, where possible, have been obtained as functions of date. January 1987 and 1989 were both characterised by clear drifts toward longer periods, with corresponding drifts in phase. At each of the summer maxima observed the period was found to be close to 48 h, with the phase of the meridional component within 3 h of local midnight. Direct comparison of local data for January 1987 with published data obtained simultaneously in Australia and Antarctica confirms the well-established westward propagation of the wave, but with an apparent zonal wavenumber somewhat smaller than the expected value of 3. It is shown that the discrepancy could arise from a combination of observational effects and a northward tilt to the wave velocity. The best result of an attempt to detect a horizontal phase gradient from local data alone is, however, more consistent with a southward tilt. There is theoretical support for both conclusions, but the matter cannot be resolved with the data presently available. It is also concluded that the background circulation at meteor heights has little influence on the wave parameters, and that indications of wave activity outside the summer season are of doubtful significance.     

Simultaneous meteor radar observations at Monpazier (France, 44°N) and Punta Borinquen (Puerto Rico, 18°N). II—Mean zonal wind and long period waves

Meteor radar wind observations have been simultaneously conducted by the CNET/CRPE meteor radar group at Monpazier (France, 44°N) and at Punta Borinquen (Puerto Rico, 18°N) in 1977–1978. The Puerto Rico results yielded some characteristics of the mean zonal wind and long period motions at low latitudes which have been compared with the characteristics of the same components observed at middle latitudes. Some differences (both time and altitude shift) are seen for the winter and spring circulation between low and mid-latitudes and even high latitudes (Kiruna, 68°N) where a CNET radar was established in 1974–1975.More energy was observed at low latitudes in the long period wave range and with the systematic existence of peaks at periods 2.5 days and between 3 and 10 days. The long period motions can be generally considered as ‘evanescent’ waves at low and middle latitudes, except during the July–August campaign in Puerto Rico.The existence of two components of 6-day and 60 h periods at both stations in March 1978 allowed us to assume that these waves were planetary waves and to study their longitudinal and latitudinal structure.     

Semidiurnal tidal winds at Collm (52°N, 15°E) and Saskatoon (52°N, 107°W) over the decade 1978–1988

Mean winds and tides have been measured by the LF and MF radar systems at Collm and Saskatoon respectively. Semidiurnal tide amplitudes and phases near 90 km evidence very similar monthly variations. A detailed comparison of mean wind and tidal profiles (85–110 km) in the Septembers of 4 years shows some differences however, which are consistent with regional (Europe-Canada) differences in the mean background winds.     

Observations of the quasi 2-day wave near 90 km altitude at Adelaide (35°S)

A quasi 2-day oscillation in the meridional winds near 90 km altitude has been observed at Adelaide (35°S) during late summer of the years 1966–1975. The mean amplitude in mid-January is 48 m s⁻¹, and the phase variation with height is indicative of a wave with downward phase propagation and a vertical wavelength greater than 100 km.     

The quasi 2-day wave at Durham (43°N): solar and magnetic effects

A quasi 2-day oscillation has been observed in the meteor winds at Durham since 1970. On a four-day basis the oscillation occurs throughout the year with amplitudes of 10 m s⁻¹ and standing wave or evanescent (λ_z > 150 km) behavior with height. During late summer the oscillation increases in amplitude to ~30 m s⁻¹ with increased phase coherence. When analyzed as a 48 h component the time of maximum of the North-South oscillation prefers the value 15 h LST implying some interaction with the solar tides. The amplitude of the 2-day component is correlated with the daily magnetic index A_p indicating magnetic activity as a possible forcing for this oscillation.     

Quasi-biennial oscillation in ionospheric parameters measured at Juliusruh (55°N, 13°E)

When seasonal variations were eliminated by evaluating 12-month running means, the ionospheric parameters foE, foF2 and hmF2 at Juliusruh (54.6°N, 13.4°E) showed large solar cycle variations. However, when further 3-yr running averages were evaluated and subtracted, QBO (Quasi-biennial oscillations) were noticed in all these parameters. Sunspot series did not reveal a QBO, but geomagnetic Ap did show a QBO. The peaks of the ionospheric QBO and QBO of Ap could be roughly compared, with lags or leads of a few months. Also, these compared roughly with the well-known QBO peaks of tropical stratospheric (50 mb) zonal winds. Similar analyses at other locations are warranted.     

Comparisons between time variations in D-region winds and electron densities at Saskatoon,Canada (52°N; 106°W)

A partial reflection radiowave system (2.2 MHz) has been used at Saskatoon, Canada (52°N, 106°W; L = 4.4) to obtain electron densities (~65–85 km) by the differential absorption experiment, and winds (52–118 km) by the spaced antenna drifts experiment. These data have been compared during the winter (December–March) of 1974/75, eleven selected days during January and February of 1976, and during 10 days in each of the four seasons of 1976. There is consistent evidence for a correspondence between increasing ionization and decreasing northward or increasing southward winds, during winter months. This is consistent with the hypothesis that nitric oxide (NO), created during magnetic storms by the associated auroral activity, contributes to electron density variability by way of circulation changes and atmospheric waves. It has not been possible to distinguish between a latitude gradient of NO or isolated accumulations of this minor constituent.     

Mesopause temperatures and integrated band brightnesses calculated from airglow OH emissions recorded at Maynooth (53.2°N, 6.4°W) during 1993

Spectra of the hydroxyl emissions in the wavelength range 1.0–1.6 μm, which originate at mesopause altitudes, have been obtained, using a Fourier transform spectrometer at Maynooth (53.2°N, 6.4°W), on all suitable nights during the period January–December 1993. Rotational temperatures and integrated band brightnesses have been calculated from the spectra of the OH(3, 1) and (4, 2) vibration-rotation bands. The mean annual temperatures calculated over all measurements were T(3, 1)=200±19 K and T(4, 2)=206±19 K, where the uncertainty represents the standard deviation on the measurements. Harmonic analysis of the nightly averaged temperature values revealed an amplitude of 27 ± 1 K and a phase of 95 ± 2 days in the annual variation of the (3, l) band at our latitude. The semiannual component was found to have an amplitude of 7 ± 1 K and a phase of −51 ± 9 days for this band. Results for the (4, 2) band were identical in both amplitude and phase for the annual component, while the semiannual component gave an amplitude of 8 ± 1 K and a phase of − 43 ± 7 days. These results are compared with data recorded by the SME satellite, and with the predictions of the MSISE-90 model for a station at 53° latitude. Temperatures predicted by the MSISE-90 model for Maynooth are consistently below the values obtained in this study by 15–20 K. Excellent agreement is observed between the absolute value of temperature, in the case of the SME satellite, and in the amplitude and phase of the annual variation predicted by MSISE-90. The phase of the semiannual component observed in our data deviates somewhat from the −99 ± 1 days predicted by MSISE-90.The annual mean brightness of the OH (3, 1) band was found to be 75 ± 18 kR, while that of the (4, 2) band was 106±26 kR. Diurnal variations generally showed a steady decrease from dusk to dawn, apart from a brief period in June and July. Monthly average values of band brightness have been calculated for each band and are compared with the predictions of a recent photochemical model (Le Texier et al., 1987). The model shows some elements of agreement with our observations, particularly a pair of maxima near the equinoxes, but it does not predict the broad winter maximum observed in both bands at this latitude.     

Saturated gravity wave spectra derived from foil chaff experiments performed during campaign ‘DYANA’ at 44°N (Biscarrosse,Southwest France)

Two series of measurements of horizontal wind velocity, one performed in winter 1990 at 44°N latitude, and the other in summer 1988 at 69°N latitude, were subjected to a spectral analysis. The two series covered a height interval of 11–15 km centred at about the same height (92.5km in winter, 91.5km in summer). In both cases the slopes of the spectra were close to −3. A dominant wavelength (if it existed) must have been larger than the height interval covered.     

The Scottish national Antarctic expedition (1902–04) and the founding of Base Orcadas

The history of the establishment of the scientific research station on Laurie Island, South Orkney Islands, is recounted. Its founding by the Scottish National Antarctic (Scotia) Expedition (1902–04) and the subsequent operation by Argentina resulted in it becoming the first all‐year‐round permanently‐staffed research facility in Antarctica. The networks of government and non‐government personnel involved in the rivalry between British and Scottish interests and aspirations and the transfer of the Laurie Island facility from the Scottish expedition to Argentine government control are investigated. The narrative is set against the background of the centennial celebrations of that transfer.     

Rotational temperatures for OH and O2 airglow bands measured simultaneously from El Leoncito (31°48′S)

Some results from 54 nights of simultaneous measurements, performed between 1984 and 1987, of rotational temperatures for the OH(6−2) and O₂(¹∑)(0–l) bands are presented. A summer enhancement by 15 K in O₂ temperature has been found that has not formerly been observed in airglow measurements. At least five nights show prominent tide-like temperature oscillations with a phase shift between layers typical of upward wave propagation at about 10 km h⁻¹, with up to 55 K variation. During other nights, similar oscillations are limited to the O₂ layer. Data for different seasons seem to be characterized by different levels of variability. During the one equinox campaign, nocturnal temperature variations show an exceptionally stable pattern of tide-like oscillations.     

Tidal winds at mesopause altitudes over Arecibo (18°N, 67°W), 5–11 April 1989 (AIDA '89)

An imaging Doppler interferometer (IDI) radar was operated during the three AIDA '89 campaigns in Puerto Rico over the period March–May of 1989. The output of the IDI analysis characterizes radar scattering in terms of a number of discrete ‘scattering points,’ also referred to as ‘multiple scattering centers,’ IDI/MSC for short. For each of these points the three-dimensional location, radial velocity and amplitude and phase are determined, similar to the output of meteor radars. We have applied the conventional Groves [(1959) J. atmos. terr. Phys. 16, 344–356] meteor wind radar analysis to the scattering points to produce the mean apparent motions over the height range from 70 to 110 km which are presented here. The mean apparent motion of the scattering centers is the quantity that would correspond to the neutral atmosphere wind or bulk motion if the scattering points are physical entities (such as turbulent eddies) whose motions are determined solely by advection. This is the quantity which is treated as the ‘wind’ in the analysis which follows and which should be compared to the wind measurements as deduced from the other methods employed during this campaign. There is, however, a caveat which supports the contention of Hineset al. [(1993) J. atmos. terr. Phys. 55, 241–287] that extreme care must be used in interpreting the velocities measured by partial reflection radars as winds. The current application of the Groves method of analysis has revealed motions from which one would infer a typical equatorial easterly circulation, with mean meridional circulation becoming significant only above 96 km. A periodogram analysis of the complete data interval (5–11 April) has shown the diurnal tide to be the most significant feature of the wind field at these altitudes, with zonal amplitudes up to some 50 m/s and meridional amplitudes approximately half this value. The 12 and 6 h tides become as significant as the diurnal above 100 km. The two day (48 ± 5 h) wave is the next most significant feature, with zonal amplitude increasing with height up to 30 m/s at 110km. The semidiurnal tide is not at all well developed below 100 km. However, analysis on a day by day basis reveals a significant semidiurnal component which is not phase coherent over the total interval. Mean vertical velocities are of the order of tens of centimeters per second and are considered to be more realistic than the meters per second velocities usually inferred from analyses of meteor trail drifts.