“Molecular weight” of air at high altitudes

Abstract

This report describes a method for obtaining the so-called “molecular weight” of air at high altitudes of the earth's atmosphere above the transition region for the dissociation of molecular into atomic oxygen. A reasonable working model, based upon the ratio of absolute temperature to molecular weight T/M, which is proportional to the slope of the loge pressure υs altitude curve, is presented. The region considered is from 90 to 600 km, assuming that the composition of the atmosphere is constant up to 90 km. The calculations are based upon experimental data reported by Byram, Chubb, and Friedman from Aerobee 16, 1 December 1953. Since the 1956 Model Atmosphere of the Air Research and Development Command employs a variable scale height gradient with altitude, the diffusive equilibrium and mixing formulas of Nicolet and Mange were modified to obtain the vertical distributions of the various atmospheric constituents. The mass densities are found by multiplying the number densities by the respective molecular mass of the individual components of the atmosphere. The molecular weights at the various altitudes were calculated from the formula Knowing the composition of the atmosphere at any altitude, it is possible to determine the temperature through the relationship of the scale height to temperature, H = RT/Mg.