Mass spectrometric studies of the composition of the lower thermosphere during summer 1967

The atmospheric composition in the altitude range between 120 and 210 km over White Sands, New Mexico (32°24′N, 106°20.6′W) has been measured by mass spectrometers in three rocket flights at 1249 MST on June 21, 1967, and at 0200 MST and 1224 MST on July 20, 1967. The day-to-night variations of the ambient number densities found are larger than the model predictions and extend down to 120 km. Diffusive equilibrium profiles for the atmospheric constituents are compared with the measured number densities. The level where the Ar/N2 ratio reaches the ground level value was computed to be at 99, 99, and 101 km for the three flights, respectively. The He number densities, when compared with results obtained in earlier flights, indicate a seasonal decrease of the He content from the winter to the summer by a factor of about 10.