Long-term trends of mesosphere/lower thermosphere gravity wave proxies derived from combined LF spaced receiver and VHF Doppler wind observations

Time series of mesosphere/lower thermosphere half-hourly winds over Collm (51.3N, 13.0E) have been obtained from 1984 2008 by low frequency (LF) spaced receiver measurements and from 2004 to date by VHR meteor radar Doppler wind observations in the height range 82 97 km. From half-hourly differences of zonal and meridional winds, gravity wave (GW) proxies have been calculated that describe amplitude variations in the period range 1 3 hours. After applying corrections to account for instrumental differences, GW climatology and time series have been obtained. The mean GW activity in the upper mesosphere shows maximum amplitudes in summer, while in the lower thermosphere GWs maximize in winter. Positive/negative long-term trends are visible in winter/summer. Interannual and quasi-decadal variations of GW amplitudes are also visible, but these are intermittent.