Indications of long-term changes in the lower thermosphere prevailing zonal wind regime

Abstract

[1] To take a new approach to the lower thermosphere (80‐100 km) long-term behavior, the variations of the dates of the equinoctial rearrangements of the zonal wind circulation were considered. We have evaluated the duration of unstable equinoctial rearrangements periods and duration of rather stable summer and winter circulation periods as well. The identical multiyear radio measurements of the horizontal winds in the lower thermosphere/ionosphere at two midlatitude (52 N) observatories (Irkutsk (Badary Observatory), East Siberia, and Collm, central Europe) during 1981‐1996 were used. It is shown that there are significant nonzonality and regional dierences in the character of the circulation rearrangements. The duration of the winter circulation in East Siberia is systematically longer than in central Europe. However, the tendency to a decrease of the summer circulation duration for the years under consideration is observed for both regions. INDEX TERMS: 0341 Atmospheric Composition and Structure: Middle atmosphere: constituent transport and chemistry; 2437 Ionosphere: Ionospheric dynamics; 2427 Ionosphere: Ionosphere/atmosphere interactions; KEYWORDS: Lower thermosphere/ionosphere; Prevailing wind; Long-term changes.