COSPAR International Reference Atmosphere Research Articles

Variations in air density from January 1972 to April 1975 at heights near 200 km

Variations in air density have been determined using the orbit of the satellite Cosmos 462, 1971-106A, which entered orbit on 3 December 1971 with an initial perigee near 230 km and inclination 65.75°, and decayed on 4 April 1975. Accurate orbits determined at 85 epochs give perigee height correct to about 200 m throughout the satellite's lifetime. Using these values of perigee height and orbital decay rates from NORAD elements, 604 values of air density at half a scale height above perigee have been evaluated. These densities have been compared with values from the COSPAR International Reference Atmosphere 1972, taking account of variations due to solar activity and geomagnetic disturbances, and day-to-night variations, to reveal the residual variations in density at a series of standard heights, 245, 240, 232 and 213 km. The main residual variation is semi-annual, with maxima usually in April and October, and minima usually in January and July; but it is irregular in phase and shape. The amplitude of the semi-annual variation is remarkably constant from year to year between 1972 and 1975, and considerably greater than that given by CIRA 1972: the April/July density ratio is 1.68, not 1.32 as in CIRA; the October–November maxima are all lower than the April maxima, whereas CIRA gives the opposite; the July minima are 18% lower than the January minima, as opposed to 10% in CIRA. A standardized semi-annual density variation for the early 1970s is presented, with January minimum of 0.94, April maximum of 1.28, July minimum of 0.77 and October–November maximum of 1.22. In addition, three other recurrent variations are recognizable: in each year the density has a subsidiary minimum in May and maximum in June; there are low values in mid November and high values in late December.

Analysis of the orbit of 1966-51C

The satellite 1966-51C was launched in June 1966 into a polar orbit with perigee height 180 km, apogee height 3600 km, and orbital period 125 min. The orbit contracted rapidly under the influence of air drag, and the satellite decayed in March 1967. The only available observations are from the NASA Minitrack system, and 825 of these have been used with PROP6 orbit refinement program, to determine orbital parameters at 20 epochs. For most of these orbits the standard deviations in inclination and right ascension of the node are less than 0.002° (corresponding to about 200 m cross-track) and the standard deviations in eccentricity are less than 0.00002 (150 m in height). The variation in inclination is analysed to determine upper-atmosphere zonal wind speeds, with excellent resolution in local time. The results, for heights near 210 km and a representative latitude near 30°, indicate west-to-east winds of 100 ± 40 m/s for local time 18–21 h, and east-to-west winds of 80 ± 25 m/s for 02–04 h and 09–12 h local time. The values of the right ascension of the node are also analysed, and provide independent confirmation of the wind speeds obtained from the inclination. Analysis of the decrease in perigree distance indicates values of density scale height within 5% of those predicted by the COSPAR International Reference Atmosphere 1972, for the conditions experienced by 1966-51C.

Dynamics and structure of the quiet thermosphere

The COSPAR International Reference Atmosphere (CIRA) 1972 provides both a Mean International Reference Atmosphere of the thermosphere and also a parametric set of models for this region. These models are based on our knowledge of the thermosphere as of mid 1971. The problem of the differences in the diurnal variation of atmospheric density scale height from satellite drag studies and temperature from incoherent radar scatter observations is probably due to different diurnal variations of density and temperature and not due to systematic discrepancies in the measurements. The answer to this question should be provided by data from the recent satellites ESRO4, AEROS and AE-C. The second major area of interest involves the absolute number densities and variation with time of day, latitude and season of the major and minor constituents of the thermosphere. Recent data obtained with mass spectrometers and optical instruments are reviewed in addition to the results of theoretical composition calculations which include turbulence and other transport effects. The new density, temperature and composition results could lead to the development of a new generation of thermospheric models.

The structure of the atmosphere up to 150 kilometre

Abstract New techniques and organized observing programmes have maintained the impetus to geophysical research proviclcd by the IGY in 1957–58. A selection of research techniques and results are discussed which illustrate this statement. Mcteorological rockets and satellites, sounding rocket observations, high-latitude phenomena and upper atmosphere structure are the main topics dealt with. Reference is made to a new COSPAR International Reference Atmosphere (CIRA 1972) which reviews and tabulates atmospheric structure above 25 km and brings the material of the previous (1965) edition up to date.

A comparative study of the wind structure in the stratosphere at Sonmiani vis-a-vis CIRA 1965

All available wind data from seventy meteorological rocket firings conducted during the period 1964–70 from Sonmiani (latitude 25°11?38” N and longitude 66°44?47” E) have been analysed for studying the zonal wind structure in the stratosphere. The salient features of the mean zonal circulation for all the months have been studied and the results compared with COSPAR International Reference Atmosphere 1965. Fluctuations in the zonal wind during winter are discussed in detail. DOI: 10.1111/j.2153-3490.1972.tb01580.x

A comparative study of the wind structure in the stratosphere at Sonmiani vis-a-vis CIRA 1965

All available wind data from seventy meteorological rocket firings conducted during the period 1964–70 from Sonmiani (latitude 25°11?38” N and longitude 66°44?47” E) have been analysed for studying the zonal wind structure in the stratosphere. The salient features of the mean zonal circulation for all the months have been studied and the results compared with COSPAR International Reference Atmosphere 1965. Fluctuations in the zonal wind during winter are discussed in detail. DOI: 10.1111/j.2153-3490.1972.tb01580.x

Flotation technique for laboratory calibration of low-level accelerometers.

References 1 Brace, L. EL, Spencer, N. W., and Dalgarno, A., Detailed Behavior of the Mid Latitude Ionosphere from the Explorer XVII Satellite, Planetary and Space Science, Vol. 13, 1965, pp. 647-666. 2 Brace, L. H., Reddy, B. M., and Mayr, H. G., Global Behavior of the Ionosphere at 1000 km Altitude, Journal of Geophysical Research, Vol. 72, 1967, pp. 265-284. 3 Dalgarno, A., McElroy, A. M. B., and Walker, J. C. G., The Diurnal Variation of Ionospheric Temperatures, ' Planetary and Space Science, Vol. 15, 1967, pp. 331-345. 4 Hanson, W. B., McKibbin, D. C., and Sharp, G. W., Some Ionospheric Measurements with Borne Ion-Traps, Journal of Geophysical Research, Vol. 69, 1964, pp. 2747-2763. 5 Kmg-Hele, D. G., The Rotational Speed of the Upper Atmosphere Determined from Changes in Orbits, Note Space 59, Feb. 1964, Royal Aircraft Establishment. 6 Mott-Smith, H. M. and Langmuir, M. S., The Theory of Collectors in Gaseous Discharge, Physical Review, Vol. 28, 1926, pp. 727-763. 7 Sagalyn, R. C., Smiddy, M., and Bhargava, Y. N., Satellite Measurements of the Diurnal Variation of Temperature in the F Region, Space Research V, North-Holland, Amsterdam, Netherlands, 1965, pp. 189-206. 8 CIRA, COSPAR International Reference Atmosphere, NorthHolland, Amsterdam, Netherlands, 1965. 9 Sagalyn, R. C. and Smiddy, M., Electron Density and Temperature Measurements in the Ionosphere, Sounding Rocket Research Technique Instrumentation Manual No. 9, edited by K. Maeda, Committee on Space Research of the International Council of Scientific Unions, Feb. 1967. 10 Sagalyn, R. C. and Smiddy, M., Positive Ion Sensing System for the Measurement of Spacecraft Pitch and Yaw, Air Force D-10 Experiment, Air Force Surveys in Geophysics No. 201, AFCRL 67-0158, Air Force Cambridge Research Labs., Dec. 1967.

Air density at heights between 130 and 160 km, from analysis of the orbit of 1968-59b

The satellite 1968-59B was a heavy sphere, of mass 272 kg and dia. 0.61 m, launched by the United States Air Force on 11 July 1968 into a polar orbit with an initial perigee height of 150 km. Despite the low perigee, the satellite remained in orbit for 38 days because of its exceptionally large mass/area ratio, and offers the opportunity of finding values of air density at heights lower than has been possible in previous studies of satellite orbits. Analysis of the orbit gives 28 values of air density, which show that the density increased from 1.49 × 10 −9 kg/m 3 at a height of 155 km to 7.9 × 10 9 kgm 3 at 130 km height. These values are in surprisingly good agreement with the COSPAR International Reference Atmosphere 1965, being about 9 per cent lower than CIRA. When the values of density are converted to a fixed height near 150 km, the day-to-day variations are found to be remarkably smooth between 12 July and 13 August, the deviations from the mean being less than 4 per cent; but there was a significant increase in density at the time of the increased solar activity centred at 15 August.

Variations in Upper Atmosphere Density at Heights of 140–180 km between July and October 1968

ACCURATE observational values of upper atmosphere density are particularly scarce at heights between 125 km and 175 km. At lower heights extensive data are available from rocket flights and other sources, and at heights from 200 km up to 1,200 km the analysis of satellite orbits has provided a fairly complete picture, specified, for example1, in the COSPAR International Reference Atmosphere 1965. The first values of density from analysis of satellite orbits at heights below 160 km, from the satellite 1968–59B launched on July 11, 1968, were reported some months ago2; these values applied at dates between July 11 and the satellite's decay on August 19, 1968. Another satellite launched at the same time, 1968–59A, which had an initial perigee height of 160 km and apogee height of 1,800 km, did not decay until November 6, 1968, and we have analysed its orbit3 to obtain values of air density at average intervals of 2 days between July and early November, chiefly at heights of 140–180 km.

Profile of Upper Atmosphere Density at Heights between 130 and 160 km, from the Orbit of the Satellite 1968–59B

ANALYSIS of satellite orbits has provided a fairly complete picture of upper atmosphere density at heights between 170 and 1,200 km, embodied, for example1, in the COSPAR International Reference Atmosphere 1965. At heights below 170 km, however, very few absolute values of air density have been obtained from orbital analysis, because satellites with perigee heights below 160 km usually decay quickly and have not yielded many useful data. Numerous measurements of air density have been made at heights between 80 and 110 km, by falling spheres ejected from rockets and other techniques. But the launchings are fewer and most of the techniques are less accurate above about 120 km. So the height range between 120 and 170 km has remained relatively uncharted.

Variations in air density at heights near 150 km, from the orbit of the satellite 1966-101G

The satellite 1966-101G was launched on 2 November 1966 into an orbit with an initial perigee height of 140 km. A satellite with such a low perigee usually decays within a few days, but 1966-101G was exceptionally dense and remained in orbit until 6 May 1967. Analysis of the changes in its orbital period provides an unique opportunity for studying continuously for six months the variations in air density at a height near 150 km. This paper records the results of such an analysis, applicable for the (medium) level of solar activity prevailing early in 1967. It is shown that at a height of 155 km the air density is greater by day than by night, with the maximum daytime density exceeding the minimum night-time density by a factor of 1.7: in contrast the COSPAR International Reference Atmosphere 1965 predicts that the density should be slightly greater by night than by day. It is also found that the night-time density increases as solar activity increases, and that the density scale height given by CIRA 1965 at heights near 150 km is too low, perhaps by about 20%.

New International Reference Atmosphere

CIRA 1965 Cospar International Reference Atmosphere 1965. Compiled by the Members of Cospar Working Group IV. (Committee on Space Research established by The International Council of Scientific Unions.) Pp. xi+313. (Amsterdam: North-Holland Publishing Company, 1965.) 54s.

Diffusion coefficients in the upper atmosphere from chemiluminous trails

Measurement of the radial growth of chemiluminous trails deposited in the upper atmosphere yields diffusion coefficients. The square of the Gaussian half-width of the cylindrical trail has been observed to increase linearly with time in the 107- to 160-km altitude region. The total inventory of radiating species varies because of chemical reactions, but this does not affect the radial growth. The measured diffusion coefficients are in good agreement with estimates using the 1965 Cospar international reference atmosphere.

Upper atmosphere wind and temperature structure by Skylark rocket-grenade experiments at Woomera, Australia, 1957—59

An account is presented of the first grenade experiments carried out at the Woomera rocket range during 1957-59. A description is given of the grenades and their rocket installation; and of the optical and acoustical instrumentation required to determine their burst positions and to find the times of travel of the sound waves to the ground. The method and theory of the experiment are outlined, and details of the firings and results obtained are presented. The accuracy of the measurements is discussed and comparisons made with simultaneous measurements by other methods. Determinations of wind speed and temperature (derived from the speed of sound) have been extended from the upper balloon limit to about 85 km, and a comparison between summer and winter conditions has been possible. Wind measurements have been extended to greater heights by means of the glow phenomenon. Pressure and density profiles have been determined and agree very closely with the COSPAR International Reference Atmosphere, 1961.

Electron density distribution in the upperFregion

A modified Chapman function with a variable scale height gradient has been found to be in good agreement with the electron density distribution obtained experimentally within the height range from about 100 km below the F2 peak to an altitude of about 700 km. The scale height distribution derived from this model is also consistent with the neutral gas scale height of the 1961 Cospar international reference atmosphere.