Physical properties of the atmosphere from 90 to 300 kilometers

Based on recent experimental and theoretical studies of the physical properties of the atmosphere at high altitudes, an average model atmosphere is presented for the region between 90 and 300 km. This model is consistent with the following assumptions: Molecular oxygen begins to dissociate appreciably only above 90 km; at around 130 km, about 30 per cent of O2 is still in the undissociated state; molecular nitrogen begins to dissociate above 220 km; the concentrations of molecular oxygen and nitrogen decrease with altitude exponentially; the temperature becomes isothermal in the region of the exosphere, approximately above 360 km. All physical quantities have been calculated from self-consistent equations as continuous functions of altitude, without assuming any particular form of the temperature gradient. The results show lower temperatures and densities throughout the region of the ionosphere than have been deduced previously.