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Worldwide predictions of h.f. and m.f. radio propagation conditions require extensive data on the space and time variations of ionospheric parameters such as foF2 and hmF2. Theoretical values of these parameters can be obtained by solving equations that represent the effects of various physical processes governing Flayer behaviour. The effects of winds, which are driven by the daily heating of the upper atmosphere, on the midlatitude F2layer are briefly described. Consideration is also given to the polar and the low-altitude F2layer and to problems of Flayer storms.