Mesosphere/lower thermosphere wind measurements over Europe in summer 1998

In July and August 1998, co-ordinated measurements of winds in the mesosphere/lower thermosphere region were carried out using meteor radars at Obninsk (Russia), Kharkov (Ukraine), Shrivenham (UK), and the low-frequency windprofiler at Collm (Germany). The strongest feature observed during this campaign was a quasi 2-day wave that appeared in the second half of July. This wave had nearly constant phase when a period of 48 h was assumed. Phase comparison between the sites revealed a zonal wave number of 4. The quasi 2-day wave event was connected with a decrease in the zonal prevailing wind, indicating wave-mean flow interaction. In addition, non-linear interaction between the quasi 2-day wave and the semidiurnal tide occurred. In August the quasi 2-day wave amplitude decreased, but other oscillations were still present. A long-period modulation of the semidiurnal tide over Europe was also observed, indicating interaction between the semidiurnal tide and a planetary wave.