Accession Number:



Variations in Air Density from January 1972 to April 1975 at Heights near 200 km.

Descriptive Note:

Technical rept.,

Corporate Author:


Personal Author(s):

Report Date:


Pagination or Media Count:



Variations in air density have been determined using the orbit of satellite Cosmos 462, 1971-106A, which entered orbit on 3 December 1971 with an initial perigee near 230 km and inclination 65.75 deg, and decayed on 4 April 1975. Accurate orbits determined at 85 epochs give perigee height correct to about 200 m throughout the satellites 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 AprilJuly 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.

Subject Categories:

  • Atmospheric Physics

Distribution Statement: