The upper mesosphere/lower thermosphere wind field nonzonality as possible sign of the external forcing from above and from below

Abstract

The geographical nonzonality of the global wind field was investigated through a long-term study of upper mesopause/lower thermosphere horizontal winds (average altitude 95 km) near Irkutsk, East Siberia, Russia (52° N, 104° E) in comparison with similar wind measurements at the stations, which are well spaced along the 52° N latitude circle. The longitudinal/regional variations in the dynamics of the upper middle atmosphere are illustrated. This effect may significantly manifest itself in the different amplitudes of the prevailing zonal wind, in the different times of the winter-spring transition of the zonal circulation, in the different response to the sudden stratosphere warmings, and in the different response to the geomagnetic storms and Solar Proton Events. The reasons of the nonzonality could be planetary scale mesopause oscillations structure; the external forcing from below due to different conditions for the generation and propagation upward of the internal atmospheric waves; the real difference of the geomagnetic latitudes. The nonzonality of the mesopause wind field may be important when empirical and physical upper atmosphere models are being formed.