Neutral air density and composition at 150 kilometers

Abstract

Mass densities derived from drag data are compared with densities determined by mass spectrometers, EUV extinction measurements, and observations of the growth of chemiluminescent clouds for an altitude of 150 km. Drag densities fall very close to the Cira 1965 mean atmosphere and are 10 to 20% higher than the average for all rocket measurements discussed. Mass spectrometric and EUV extinction measurements agree quite well for n(N2) and n(O2) but differ significantly for n(O). In order to derive an improved set of parameters of thermospheric density and composition, it is proposed that the Cira 1965 mean density be lowered by 10%, that the measured n(N2) and n(O2) number densities be maintained, and that n(O) be chosen such that the number densities become consistent with the mass density p. This results in the following reference set for 150-km altitude: ρ = 1.96 × 10−12 g cm−3; n(N2) = 2.6 × 1010 cm−3; n(O) = 2.3 × 1010 cm−3; n(O2) = 2.5 × 109 cm−3; n(Ar) = 5 × 107 cm−3; mean molecular weight M = 22.9 g mole−1.