Variations with season and latitude of density, temperature, and composition in the lower thermosphere

Analysis of neutral density data has made it possible to extend curves of mean density as a function of latitude and season from 90 to 120 km. There is an approximate isopycnic point at 91 km. Above this point the density variations are reversed from what they are at 80 km. In other words, at 120 km the density in summer and at the tropics is lower than that in CIRA 1965 and in winter the density is higher. The density curves have been idealized near 120 km to join at one of three points. These correspond to typical summer and tropical conditions, winter conditions, and spring/autumn conditions. The summer density is 20 percent below that of the U.S. Standard, the winter density is 50 percent above the Standard and the spring/autumn density is 1 percent above the Standard. By application of appropriate theory the corresponding variations in temperature and mean molecular weight have been calculated. An unexpected result of the theory is the prediction of a seasonal variation of the mean molecular weight. Some of the data presented in the paper have been analyzed since the models were derived. These data have been found to be acceptably close to the models. (Author).