Air density at heights of 150–300 km in the years 1962–1964

Abstract

A previous paper (1) traced the variation of upper-atmosphere density at heights of 200–800 km over the half-cycle of solar activity from 1958 to 1964, using the orbits of 46 satellites. Because of lack of data, however, very few values were obtained at heights below 250 km at times of low solar activity, 1962-4. The aim of the present paper is to fill this gap by evaluating day- and night-time densities at heights between 150 and 300 km during the period of low solar activity from July 1962 until November 1964. The orbits of 11 further satellites are used for the purpose: the mass/area ratio of each is found from the orbital behaviour when perigee is at a height where air density is known, and values of air density are then determined at lower altitudes, towards the end of the satellite's life. The results show that the day-to-night variation in air density remains appreciable down to below 200 km height : the maximum daytime density exceeds the minimum night-time density by a factor which decreases from 2·1 at a height of 250 km, to 1·7 at 200 km and probably about 1·4 at 180km.