Neutral composition measurements between 90‐ and 220‐km altitude by rocket‐borne mass spectrometer

On June 29, 1974, at 1514 LST a neutral gas mass spectrometer with a cryogenically cooled ion source was flown above Wallops Island as part of the Aladdin 74 program. This paper presents the obtained density height profiles of N2, O2, O, and Ar. The maximum of the atomic oxygen density was 6.5 × 1011 cm−3 at 97.5-km altitude. The altitude where the n (Ar)/n(N2) ratio reaches the sea level value was found to be about 98 km. Above 104-km altitude the densities of all constituents showed a more rapid decrease than that predicted by the Jacchia 71 model. At 112.5 km the ratio of the total mass density and the model value reached a minimum of 0.33. This and other measurements suggest a high degree of variability in the lowest part of the thermosphere.