Seasonal and inter-annual variability of the quasi 2 day wave over Collm (51.3° N, 13° E) as obtained from VHF meteor radar measurements
The quasi 2 day wave (QTDW) over Collm (51° N, 13° E) has been studied between September 2004 and September 2013 using a VHF meteor radar. The 9 year mean amplitudes show a strong summer maximum with several irregular bursts and much weaker winter maxima. In summer, the meridional amplitude is slightly larger than the zonal one with about 15 m s −1 at 91 km height. Phase differences are slightly higher than 90°, which indicates a polarization that is nearly circular. On an average the QTDW is amplified after a maximum of zonal wind shear. This can be realized in the summer mesospheric jet where the zonal wind component has its minimum or, in other words, the easterly jet maximizes. Thus, instability is found as a likely forcing mechanism. QTDW amplitudes exhibit considerable inter-annual variability. In particular, there is a possible relation between the QTDW amplitude and the 11-year solar cycle in winter but not in summer.