The rotational speed of the upper atmosphere

This paper describes the method for determining the rotational speed of the Earth's upper atmosphere from the changes in the orbital inclinations of satellites, and briefly reviews the observational results so far obtained at heights above 180 km, both by this method and by measuring the movements of vapour trails. The results from satellite orbits indicate that the upper atmosphere at heights of 200–300 km is on average rotating 1.3 times faster than the Earth, corresponding to a mean west-to-east wind of about 100 m/s in mid latitudes. The physical processes which may control upper-atmosphere movements are outlined, and possible mechanisms for the observed motions are briefly discussed. It should be emphasized that the subject is full of uncertainties, and this paper is intended to draw attention to the difficulties, rather than to provide a coherent picture of the actual conditions.