On the behaviour of wind systems in the upper mesopause region in winter and during the transition from winter to summer conditions

Abstract

Ionospheric drift measurements in the L.F. range have been carried out to examine the phase changes of the semidiurnal tidal wind in the upper mesopause region during winter and during the transition from winter to summer conditions. The observed phase changes do not appear to be predetermined by the initial situation and there is no distinct reciprocal relation between the processes in autumn and in spring. These studies are of interest because certain typical phase changes in the semidiurnal tidal wind can be regarded as a sensitive indicator of the start-time and the character of the seasonal reversals of high-atmospheric circulation systems.