The doppler wind and temperature system of the ALOMAR lidar facility: overview and initial results

The Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) facility is a new and major facility for atmospheric research. It is located at Andøya in Northern Norway. One of the important facilities of ALOMAR is the Doppler Wind and Temperature System (DWTS). The DWTS will determine atmospheric wind and temperature profiles between about 8 and 90 km altitude from the Doppler shift and broadening of the lidar signal Rayleigh back-scattered from the atmosphere. The DWTS uses a double-etalon Fabry-Perot interferometer to perform the high-resolution spectral analysis of the back-scattered lidar signal, and to reject the bright background light from the daytime sky. After spectral analysis, the Fabry-Perot fringes are imaged onto a multi-ring anode imaging photon detector which provides, pulse-by-pulse, time-resolved detection of the spectrum of the laser light back-scattered from the atmosphere. The double-etalon Fabry-Perot interferometer has been designed to detect the returned signal during daytime, and thus summer-time conditions at ALOMAR, as well as during night-time. The entire optical system has been designed to maximise the transmission and detection of light, to make maximum use of the faint signals available from high-altitude regions, up to around 80–90 km. This paper reports on the objectives and design of the ALOMAR DWTS, and presents some initial results obtained during commissioning periods in October 1994 and January 1995.     

Gravity-wave motions in the mesosphere and lower thermosphere observed at Mawson,Antarctica

We present the results of MF radar observations of mean winds and waves in the height range 78–108 km at Mawson (67°S, 63°E), Antarctica. The measurements were made in the period from 1984 to 1990. Climatologies of the prevailing zonal and meridional circulations made with a 12-day time resolution show that the mean circulation remained relatively stable over the 6 yr of observation. Climatologies of gravity-wave motions in the 1–24 h period range were also generated. These reveal that the r.m.s. amplitudes of horizontal wave motions near the mesopause (~90 km) are about 30 m s⁻¹, and that there is some anisotropy in the motions, especially at heights below 90 km. Meridional amplitudes are larger than zonal amplitudes, which suggests a preference for wave propagation in the north-south direction. Comparisons with MST radar wind observations made near the summer solstice at Poker Flat, Alaska (65°N) and at Andøya, Norway (69°N) show similarities with the Mawson observations, but the wave amplitudes and mean motions are larger in magnitude at the northern sites. This suggests hemispheric differences in wave activity that require further study.     

Positive ion composition in the lower ionosphere at high latitudes during MAP/WINE

Positive ion composition, total ion and electron density and ion production by energetic electrons were measured by rocket-borne experiments above Andøya (69.3°N, 16.0°E) in northern Norway. Observed altitudes of transition from molecular ions to proton hydrates and from electrons to negative ions are compared to results from an ion-chemical model. Nitric oxide and water vapour densities are inferred from the ion composition.     

Electrodynamic response of the middle atmosphere to auroral pulsations

On the nights of 21 and 28 October 1987, two Nike Orion payloads (NASA 31.066 and 31.067) were launched from Andøya, Norway, as part of the MAC/EPSILON campaign, to study the effect of auroral energetics on the middle atmosphere. Each payload carried detectors to measure relativistic electrons from 0.1 to 1.0MeV in 12 differential energy channels, and bremsstrahlung X-rays from >5 to >80keV in 5 integral channels. In addition, instrumentation to measure bulk ion properties and electric fields was also carried by these and/or near simultaneous flights. Flight 31.066 was launched during the recovery phase of a moderate magnetic substorm, during relatively stable auroral conditions. Flight 31.067 was launched during highly active post-break-up conditions during which Pc 5 pulsations (> 150s period) were in progress. The energetic radiation of the first event was composed almost entirely of relativistic electrons below 200 keV with negligible contributions from bremsstrahlung X-rays, while the radiation of the second event was dominated by much softer electrons ( < 100 kcV), which produced high X-ray fluxes that exceeded the cosmic ray background as an ionizing source down to altitudes below 30 km. Simultaneous conductivity measurements during both events show consistency with the ionizing radiations, with the pulsation event producing free electrons down to 55 km. far below their expected altitude range during night-time. These comparisons are discussed to evaluate the impact of such events on the middle atmosphere.     

Tidal wind observations with incoherent scatter radar and meteorological rockets during MAP/WINE

Measurements of winds in the mesosphere and lower thermosphere were carried out during the main phase of the MAP/WINE project in January and February 1984 with the EISCAT UHF incoherent scatter radar near Tromsö, Norway, and with meteorological rockets launched from the Andøya Rocket Range, Norway. The radar measurements yield wind profiles between the altitudes of about 80 km and 105 km and the rockets between about 60 km and 90 km. Results from both techniques are combined to yield mean profiles which are particularly evaluated in terms of tidal variations. It is found that the semidiurnal tide constitutes an essential wind contribution between 85 km and 105 km. Whereas the tidal amplitudes are below 5 m s⁻¹ at about 80 km, they increase to 20–30 m s⁻¹ at 100 km. The average vertical wavelength of 35 km points to the S₄² mode, but coupling and superposition of different modes cannot be excluded.     

Recent measurements of middle atmospheric electric fields and related parameters

In 1989, two series of rocket measurements were carried out to investigate middle atmosphere electric fields. The measurements were taken both in the Northern Hemisphere on Heiss Island (80°37′N and 58°03′E) and in the Southern Hemisphere in the Indian Ocean (40–60°S and ~45°E) on board the research vessel ‘Akademik Shirshov’. Along with the vertical electric fields, aerosol content and positive ion density were also measured. Some of the rocket launches were made during the extremely strong solar proton events (SPE) of October 1989. The experiments showed the strong variability of the electric fields in the middle atmosphere at polar and high middle latitudes. In all the measurements the maximum of the vertical electric field height profile in the lower mesosphere was observed to be more than ~ 1 V/m. The electric field strength and the field direction at maximum varied considerably among the launches. A maximum value of + 12 V/m was detected at a height of about 58 km at 58°30′S on 21 October 1989 during the SPE. The simultaneous measurements of the electric field strength, positive ion density and aerosols point out both an ion -aerosol interaction and a connection between the mesospheric electric fields and aerosol content.     

Mesospheric temperatures and the OH layer height as derived from ground-based lidar and OH1 spectrometry

Night-time mesospheric temperatures were simultaneously determined from the Doppler broadening of the D₂ resonance line of atmospheric sodium excited by a laser and from the rotational distribution of the P₁(1), P₁(3) and P₁(4) lines of the OH(3,1) band by an i.r. spectrometer. Both instruments were located at the Andøya Rocket Range (69°N, 16°E). The mesospheric temperature gradient permits determination of the altitude of the OH¹ emitting layer from a comparison of the equivalent layer temperatures calculated from the height-resolved Na Doppler temperatures with the observed OH¹ rotational temperatures. The altitude of the OH¹ layer maximum is determined with an accuracy of ±4 km. For 3 nights in January 1986 the OH¹ emission layer is found near an altitude of 86 km.     

Rocket-borne measurements of atmospheric infrared fluxes

In the Energy Budget Campaign two rockets, one from Andøya Rocket Range, Norway, and one from Esrange, Sweden, each carrying a liquid helium cooled infrared spectrometer, were simultaneously launched as part of salvo B. The launches occurred during the recovery phase of the last of four auroral magnetic events after a Joule heating criteria was exceeded. At Andøya, zenith radiance altitude profiles were obtained of nitric oxide (NO) near 5.4μm from 70 to 185 km (rocket apogee), of ozone (O₃) near 9.6 μm from 70 to 105 km (instrument sensitivity) and of carbon dioxide (CO₂) near 15 μm from 70 to 150 km (instrument sensitivity). Measured CO₂ spectra at 72 km are shown to compare favorably to those calculated for local thermodynamic equilibrium conditions and instrument resolution. By comparing Andøya and Esrange CO₂ radiance profiles it is shown that there is evidence for spatial variation in the emission. Further, it is shown that the very disturbed conditions of salvo B prior to and during these launches appears to have significantly changed the O₃ 9.6μm radiance profiles compared to previous rocket measurements in polar disturbed and quiet atmospheres. Using the nitric oxide radiance profiles and spectrum, previous rocket results and computed models it is shown that no radiance increase could be detected from prompt auroral energy deposition. The results support the thesis that the NO density in auroral regions is significantly enhanced over mid-latitude values and that for weak auroras, the reaction NO(v = 0) + O → NO(r = 1) + O is the dominant radiation mechanism.     

EISCAT incoherent scatter radar observations and model studies of day to twilight variations in the D-region during the PCA event of August 1989

An intense solar proton event causing enhanced ionization in the ionospheric D-region occurred on 12 August 1989. The event was partially observed during three successive nights by the EISCAT UHF incoherent scatter radar at Ramfjordmoen near Tromsa, Norway. Ion production rates calculated from GOES-7 satellite measurements of proton flux and a detailed ion chemistry model of the D-region are used together with the radar data to deduce electron concentration, negative ion to electron concentration ratio, mean ion mass and neutral temperature in the height region from 70 to 90 km, at selected times which correspond to the maximum and minimum solar elevations occurring during the radar observations. The quantitative interpretation of EISCAT data as physical parameters is discussed. The obtained temperature values are compared with nearly simultaneous temperature measurements at Andøya based on lidar technique.     

Middle atmosphere electrical structure during MAC/EPSILON

Extensive use of rocket-launched probes during the MAC/EPSILON campaign at the Andøya Rocket Range, Norway, has enabled the characterization of the region's electrical environment for all four flight series. The first rocket salvo was conducted during daylight (15 October 1987) and the subsequent three occurred at night (21 and 28 October and 12 November 1987), all of them during geomagnetically disturbed conditions. Measurements of polar electrical conductivity, ion mobility and number density are presented, and their associated structure is investigated for local auroral ionization effects. This is believed to be the first time that Gerdien condenser mobility measurements have indicated a heavy-ion presence (positively charged aerosols) in the auroral mesopause region.     

Fine structure and dynamics of the Harang discontinuity: An event study

Two rockets were launched simultaneously from the Andöya Rocket Range in northern Norway into and through a Harang discontinuity region during a small isolated substorm. Each was equipped with an array of instruments for monitoring ionospheric electric fields and auroral particles. Different sized rockets allowed both to traverse a range of 300 km while introducing altitude separations of up to 440 km, and separations between the feet of the magnetic field lines intersecting the payloads of up to 100 km. The data sets, coupled with multi-station ground-based observations, provide information on the structure and dynamics of the Harang discontinuity region. Two boundaries were encountered. The first electric field reversal was observed simultaneously by both payloads in a region of weak precipitation, while the second reversal was associated with an intense auroral band. Since an unambiguous interpretation of these data is not possible, we present two alternative scenarios. In one the discontinuity becomes realigned during the flight following a decay in the activity. The second involves a triple cell convection system, possibly the result of an eddy in the flow.     

Studies of middle atmosphere dynamics: the research projects Middle Atmosphere Co-operation/Summer in Northern Europe (MAC/SINE), and MAC/EPSILON

The Earth's middle atmosphere covers the height region 10–100 km and has been extensively studied in recent years. The international programmes Middle Atmosphere Program (MAP) and Middle Atmosphere Co-operation (MAC) have made significant contributions to our understanding of this part of the atmosphere. This special issue reports on the results from two campaigns, MAC/SINE and MAC/EPSILON, carried out within the framework of MAP and MAC. The two projects both studied the dynamical state of the middle atmosphere at high latitudes and had different, but complementary, aims:

• 1.1. Middle Atmosphere Co-operation/Summer in Northern Europe (MAC/SINE) studied the general circulation and temperature structure as well as waves, turbulence and winds in high latitudes during summer solstice conditions. The experiments comprised a series of regular meteorological rocket firings and ground-based observations as well as four launches of sounding rockets. The campaign was carried out in July-August 1987.
• 2.2. MAC/EPSILON was a case study of middle atmosphere turbulence by means of instrumented sounding rockets, meteorological rockets and ground-based observations. The campaign comprised four salvoes in which all rocket and ground-based techniques were concentrated in time and space to make detailed measurements during events with strongly developed turbulence. During the campaign period the ground-based techniques were exploited to map the general behaviour of the middle atmosphere during autumn/early winter conditions. The campaign was carried out in October–November 1987.

Both campaigns were very successful and yielded a number of significant and interesting results, as demonstrated in the 21 articles in this special issue.     

Thermodynamics and electrodynamics of the auroral E-region during the D salvo of the MAP/WINE campaign

With the help of incoherent scatter (EISCAT) data the thermodynamics and electrodynamics of the auroral E-region north east of Andøya Rocket Range has been investigated between 1740 UT and 2040 UT on 31 January 1984. This time period covers the D salvo of MAP/WINE and the EISCAT incoherent scatter data comprise a useful supplement to interpret the rocket data. Good agreement has been found between the EISCAT temperatures and those derived from mass spectrometer data. Neutral wind velocity estimates from EISCAT and from a falling sphere rocket experiment are in satisfactory agreement for the zonal wind component, but disagree for the meridional component.     

Measurements of odd oxygen in the polar region on 10 February 1984 during MAP/WINE

Abundances of atomic oxygen and ozone have been measured by various techniques over northern Scandinavia during the MAP/WINE campaign in the winter 1983–1984. On 10 February at Kiruna, Sweden, rocket experiments used resonance fluorescence and twin path absorption at 130 nm to measure [O]between 70 and 178 km. Rocket-borne measurements of nightglow at 557.7, 761.9 and 551.1 nm and at 1.27 μm have also been obtained and [O]values derived from the atmospheric band intensities. Ozone abundances between 50 and 90 km have been determined from rocket-borne measurements of the ν₃ 9.6 μm nightglow intensity from Andøya, Norway, and Kiruna. These have been compared with [O₃] measured on the same day from the Solar Mesospheric Explorer satellite, using measurements of dayglow at 1.27 μm, and with results from other rocket launchings in MAP/WINE. The results show evidence of low, perhaps exceedingly low, [O] and below normal [O₃] above the mesopause. Below 75 km at night [O₃] exceeded earlier and subsequent observations in the campaign. The measurements were made during a minor stratospheric warming, characterised by an offset polar vortex centred near the measurement zone.     

First low-power VHF radar observations of tropospheric,stratospheric and mesospheric winds and turbulence at the Arecibo Observatory

First VHF radar measurements with height resolution of 300 m and angular resolution of 1.7° were carried out in low latitudes at the Arecibo Observatory, Puerto Rico. A short outline is given of the experimental set-up which consisted of a 160W average power radar-transceiver and a self-contained digital radar control and data acquisition unit. The new VHF feed system of the Arecibo dish is described shortly. Reliable radar echoes were detected from the troposphere, lower stratosphere and from some heights in the mesosphere, indicating that the described VHF radar is capable of proper investigations of dynamical processes in the low latitude middle atmosphere. The angular dependence of aspect sensitive tropospheric and stratospheric turbulence structures was measured to be 1.5–2.5 dB degree⁻¹. Echoes from the mesosphere indicate a patchy structure of turbulence. The analysis of the signal-to-noise ratio shows considerably high reflectivity in the upper troposphere, which can be caused by high-reaching tropical cumulus convection. Wind profiles measured with the VHF radar between 7.5 and 19.5 km with a height resolution of 300m are very similar to radiosonde wind profiles. Mesospheric VHF radar winds are roughly consistent in amplitude with tidal winds.     

Recurrent propagating auroral forms in pulsating auroras

Observations of pulsating auroras with an all-sky Isocon TV system made from Poker Flat Research Range, Alaska, and Andøya rocket range, Norway, have revealed that auroral forms propagating like waves, (here termed recurrent propagating auroral forms) predominantly in the meridional direction, are a significant proportion of the group of auroras commonly labelled pulsating auroras. The wavelike forms are described and compared with pulsating patches. Characteristics of the two types differ sufficiently, that the possibility of different mechanisms should be considered. Propagation of the wave forms continues up to discrete arcs on the poleward edge of the diffuse aurora. One example is presented where no enhancement was observed within black aurora when the wave forms encountered this on their propagation path.     

Daytime mesospheric temperatures over the low-latitude station Thumba derived from rocket-borne solar Lyman-α absorption measurements

Molecular oxygen concentrations obtained from the rocket measurements of the absorption profile of solar Lyman-α radiation, in the upper atmosphere over Thumba (8°33′N, 76°52′E), have been used to derive gas temperatures in the 70–90 km altitude region. A mean reference temperature profile for the daytime mesosphere over Thumba obtained from these measurements shows (1) temperatures lower than those given by the CIRA model and (2) a mesopause around 83 km with a temperature of 175 K.     

Mean state and long term variations of temperature in the winter middle atmosphere above northern Scandinavia

Stratosphere and mesosphere temperatures were measured during four winter months (November–February) at high latitudes (Andøya, ESRANGE) by means of numerous rocket flights during the Energy Budget Campaign 1980 and the MAP/WINE Campaign 1983–1984. They are compared to ground-based OH¹ measurements and SSU satellite data. The atmosphere was found to be very active, with several minor and one major stratospheric warming occurring. A harmonic analysis of the temperature oscillations observed is performed and found to be suitable to model the atmospheric disturbances (warmings) to a large extent by superposition of waves with appropriate periods. These periods are of the order of several days and weeks and are thus similar to those of planetary waves. Stratospheric warmings tend to be correlated with mesospheric coolings, and vice versa. This is reproduced by the model, giving details of the phase relationships as they depend on altitude. These are found to be more complicated than just an anticorrelation of the altitude regimes. Strong phase changes occur in narrow altitude layers, with oscillation amplitudes being very small at these places. These ‘quiet layers’ are frequent phenomena and are independently found in the data sets of the two campaigns. They are tentatively interpreted as the nodes of standing waves.The time development of temperature altitude profiles shows strong variations that lead to peculiar features, such as a split stratopause or a near-adiabatic lapse rate in the mesosphere on occasion. The superposition model is able to reproduce these features, too. On one occasion it even shows super-adiabatic temperature gradients in the lower mesosphere for several days. Though this should be taken as an artifact, it nevertheless suggests a considerable contribution of the long period waves to atmospheric turbulence.The many rocket data are also used to determine monthly mean temperature profiles. These are compared to reference atmospheres recently developed for the CIRA (Barnett and Corney, 1985; Groves, 1985). Fair agreement is found, which is much better than with CIRA (1972). This is not true for February 1984, because of the major warming that occurred late in that month. Before this warming took place, atmospheric preconditioning appears to have been present for more than two months.     

The ionosphere: morphology,development and coupling

The morphology of the MAP/WINE winter is examined, principally from ground-based and satellite observations. Winter anomaly is evident, occurring in bursts with a west to east shift in time. Auroral activity, particularly with reference to the times of major rocket salvoes, is generally low, with Andøya to the south of the auroral boundary in most cases. Minor stratospheric warmings, of which 4 occurred, are found to correlate with minima in radio wave absorption. Salvo R1 was launched during one of the minor warmings.Using data from a broad sector of Europe, coupling between the lower thermosphere and mesosphere is seen over large areas. Westerly winds are associated with high absorption (winter anomaly) and reversal to easterly winds with stratospheric warmings and low absorption. It is found possible to select cases, from amongst the MT series of rocket launchings, corresponding to quiet conditions, stratospheric warming, winter anomaly and particle precipitation in the general absence of other effects. Examining D- and lower E-region ionisation profiles for these caes it is found that, compared with a quiet night, the stratwarm night shows the lower E-region to have reduced ionisation. The ionisation ledge is of similar shape in all cases, but occurs over different height ranges. The observed effects all point to transport being a major factor and the need to measure vertical transport over the range of geophysical conditions examined is highlighted.     

Source regions of medium scale travelling ionospheric disturbances observed at mid-latitudes

The characteristics of medium scale travelling ionospheric disturbances (MSTIDS) have been determined from observations carried out between 1972 and 1975 at Leicester U.K. (52°32′N, 1°8′W) using the HF Doppler technique. By reverse ray tracing through a model atmosphere an estimate of the source locations of these waves can be obtained. Auroral sources do not appear to represent an important generation mechanism for MSTIDs observed at mid-latitudes. The majority of waves originate at tropospheric altitudes at ground ranges of less than 1500 km from the observation point, and a moderate correlation is found between the occurrence frequency of MSTIDs and the intensity of the meteorological jet stream.