Upper atmosphere physical characteristics

Recent physical data concerning the constitution of the upper atmosphere and solar emissions are used in a discussion regarding some properties of the ionospheric regions. Numerical values are given for the electron collision frequency as a function of height. The transition region of dissociation of molecular oxygen is considered and the dissociation of molecular nitrogen is studied. Diffusive separation is shown to contribute to the vertical distribution of the atmospheric constituents. The penetration of relevant solar radiation is discussed with respect to the formation of ionospheric layers.