Variations in exospheric density at heights near 1100km, derived from satellite orbits
TL;DR: In an earlier paper as mentioned in this paper, values of exospheric density were obtained from the orbit of Echo 2 for the years 1964-1965, and the results indicated a semi-annual variation in density by a factor of between 2 and 3, considerably larger than predicted by existing atmospheric models.
About: This article is published in Planetary and Space Science.The article was published on 1967-12-01. It has received 17 citations till now.
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TL;DR: In this article, a series of measurements of neutral atmospheric wind velocity, turbulent structure, temperature and density were made during each launch between 90 and 250 km altitude, combining the experimental techniques of the two groups involved.
Abstract: Two Skylark rockets were launched from Woomera rocket range, Australia (31 degrees S) on the morning and evening of 31 May 1968. Coordinated series of measurements of neutral atmospheric wind velocity, turbulent structure, temperature and density were made during each launch between 90 and 250 km altitude, combining the experimental techniques of the two groups involved. This paper attempts to construct from the combined measurements made on these occasions a dynamic picture of the interactions of atmospheric structure, and to relate the observations to previous results obtained by ourselves and other workers.
57 citations
01 Apr 1969
TL;DR: In this article, a coherent transponder between a pair of satellites at a frequency of 5 GHz was used to record changes of 3 cm in the phase path, giving a sensitivity to changes in atmospheric density of 1:18 000.
Abstract: A pair of satellites in the same earth orbit but separated by about 60° in phase will have a radio path between them that intersects the atmosphere continuously. With a coherent transponder between satellites at a frequency of 5 GHz, changes of 3 cm in the phase path can be recorded, giving a sensitivity to changes in atmospheric density of 1:18 000. With a set of six satellites to sense density at five levels, sufficient resolution is acquired to define the vertical density profile for weather prediction equations. Three such systems in polar orbit will give the necessary world-wide resolution every 12 hours. Actual motion of the satellites due to orbit perturbations can be corrected for, giving air pressure accuracy better than 3 mbars with existing knowledge of the earth's gravity and with long term averaging of data from the satellites' own transponders. Below about 7 km, correction must be made for water vapor effects on the radio waves. Several techniques are available to extend the desired precision down to 5 km and may be able to give the necessary corrections down to 3 km.
41 citations
TL;DR: The air density at a height of 191 km between 14 June 1966 and 5 July 1967 has been evaluated by analysing the orbit of the satellite Secor 6 (1966-51B) as discussed by the authors, showing that nearly all geomagnetic disturbances are accompanied by increases in density, of larger magnitude than expected Surprisingly, however, the strong 27-day recurrence tendencies in solar activity, as represented by the 107-cm radiation energy, are quite absent from the density variations.
35 citations
TL;DR: In this article, the authors decomposed the semiannual density variation into Fourier terms to find out the physical nature of this effect and deduced different height profiles for the two Fourier components which suggests that both components originate from different energy sources.
21 citations
TL;DR: In this paper, the orbits of five satellites have been analyzed to reveal the semi-annual variation in air density at heights between 300 and 505 km during the period of high solar activity in 1967 and 1968, and the results combined with data from other satellites.
16 citations
References
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TL;DR: In this paper, the proper interpretation of irregular motions in the upper atmosphere has been investigated by a variety of techniques, but their proper interpretation has yet to be established. But their proper meaning has not yet been established.
Abstract: Irregularities and irregular motions in the upper atmosphere have been detected and studied by a variety of techniques during recent years, but their proper interpretation has yet to be established...
1,886 citations
TL;DR: In this article, the drag of artificial earth satellites is reconsidered in the light of recent studies of gas-surface interactions and atmospheric composition between heights of 140 and 400 km at low solar activity or heights of 600 km at high solar activity.
259 citations
TL;DR: In this paper, the average time delay between the peak of the geomagnetic perturbation and that of the atmosphere is 6.7±0.3 hours, and for latitudes smaller than 25° (average: 25°) it is 7.2± 0.5 hours.
Abstract: The density variations that accompany geomagnetic disturbances have been studied by analyzing the drag of three satellites with high orbital inclination (Injun 3, Explorer 19, and Explorer 24) and one with moderate inclination (Explorer 17). The average time delay between the peak of the geomagnetic perturbation and that of the atmosphere is 6.7±0.3 hours. While there seems to be no significant dependence on the time delay on the intensity of the perturbation and on the geographic location with respect to the sun, there appears to be some dependence on latitude. For latitudes greater than 55° (average: 65°) the mean time delay is 5.8±0.5 hours, and for latitudes smaller than 55° (average: 25°) it is 7.2±0.3 hours. All three high-inclination satellites give consistently smaller delay times at high latitudes. The observed density changes are interpreted as being caused by changes in temperature. For smaller perturbations (Kp < 5) the temperature T shows a nearly linear dependence on Kp, and for latitudes lower than 55° the rate of change ΔT/ΔKp is about 28°. For latitudes above 55° (average: 65°) ΔT/ΔKp seems to be about 15–25% greater. For more intense disturbances (Kp ≥ 5), ΔT/ΔKp is systematically larger, confirming the nonlinearity of the relation between T and Kp, when considered over its total range; there is also a good indication that some atmospheric perturbations are enhanced in the auroral zones more than others.
120 citations
TL;DR: Atmospheric data from Explorer XVII mass spectrometer, giving data analysis converting ion currents into number densities of ambient constituents as discussed by the authors, showing that ion currents in the atmosphere are highly correlated with ambient constituents.
58 citations
TL;DR: In this paper, the effect of air drag on satellite orbits of small eccentricity (< 0$\cdot $2) was studied in part I on the assumption that the atmosphere was spherically symmetrical.
Abstract: The effect of air drag on satellite orbits of small eccentricity (< 0$\cdot $2) was studied in part I on the assumption that the atmosphere was spherically symmetrical. In reality the density of the upper atmosphere depends on the elevation of the Sun above the horizon and has a maximum when the Sun is almost overhead. In the present paper the theory is extended to an atmosphere in which the air density at a given height varies sinusoidally with the geocentric angular distance from the maximum-density direction. Equations are derived which show how perigee distance and orbital period vary with eccentricity throughout the satellite's life, and how eccentricity varies with time. Expressions are also obtained for lifetime and air density at perigee in terms of the rate of change of orbital period. The main geometrical parameter determining the long-term effect of this day-to-night variation is the angular distance $\phi \_{p}$ of perigee from the maximum-density direction. Results are obtained for $\phi \_{p}$ constant and $\phi _{p}$ varying linearly with time.
43 citations