Thermal diffusion in the F2-Region of the ionosphere

Abstract

In order to examine the effects of thermal diffusion on F2-region ion densities we have evaluated ordinary and thermal diffusion coefficients to the second approximation of Chapman and Cowling for a partially ionized atomic oxygen plasma. Our results show that the thermal ambipolar diffusion coefficient, like the ordinary ambipolar diffusion coefficient, is not significantly affected by the electrons. Its value is determined almost entirely by ion-neutral interactions. We have solved the steady state continuity equation of the oxygen ions for typical mid-latitude daytime conditions and find that thermal diffusion acts to reduce the ion density at 600 km by 24 per cent. At altitudes above 300 km diffusion of the minor ions, H +, He + and N + is not influenced by the neutral species, and the ordinary and thermal diffusion coefficients of these ions may be evaluated for a fully ionized plasma. Our solutions of the continuity equations of these ions show that, at 700 km, the effect of thermal diffusion is to reduce the density of H + ions by 46 per cent, to reduce the density of He+ ions by 22 per cent, and to increase the density of N + ions by more than a factor of 2.