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 N 2 , O 2 , O, and Ar. The maximum of the atomic oxygen density was 6.5 × 10 11 cm −3 at 97.5‐km altitude. The altitude where the n (Ar)/ n (N 2 ) 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.