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Meteor radar observations of mesosphere/lower thermosphere (MLT) daily temperatures have been performed at Collm, Germany since August 2004. The data have been analyzed with respect to long-period oscillations at time scales of 2--30 days. The results reveal that oscillations with periods of up to 6 days are more frequently observed during summer, while those with longer periods have larger amplitudes during winter. The oscillations may be considered as the signature of planetary waves. The results are compared with analyses from radar wind measurements. Moreover, the temperature oscillations show considerable year-to-year variability. In particular, amplitudes of the quasi 5-day oscillation have increased during the last decade, and the quasi 10-day oscillations are larger if the equatorial stratospheric winds are eastward. [ABSTRACT FROM AUTHOR]

The quasi 2-day wave (QTDW) at 82-97 km altitude over Collm (51° N, 13° E) has been observed using a VHF meteor radar. The long-term mean amplitudes calculated using data between September 2004 and August 2014 show a strong summer maximum and a much weaker winter maximum. In summer, the meridional amplitude is slightly larger than the zonal one with about 15ms-1 at 91 km height. Phase differences are slightly greater than 90° on an average. The periods of the summer QTDW vary between 43 and 52 h during strong bursts, while in winter the periods tend to be more diffuse. On average, the summer QTDW is amplified after a maximum of zonal wind shear which is connected with the summer mesospheric jet and there is a possible correlation of the summer mean amplitudes with the background wind shear. QTDWamplitudes exhibit considerable inter-annual variability; however, a relationship between the 11-year solar cycle and the QTDW is not found. [ABSTRACT FROM AUTHOR]

After a historical survey of space related EUV measurements in Germany and the role of Karl Rawer in pursuing this work, we describe present developments in EUV spectroscopy and provide a brief outlook on future activities. The group of Karl Rawer has performed the first scientific space project inWestern Europe on 19th October 1954. Then it was decided to include the field of solar EUV spectroscopy in ionospheric investigations. Starting in 1957 an intensified development of instrumentation was going on to explore solar EUV radiation, atmospheric airglow and auroral emissions until the institute had to stop space activities in the early nineteen-eighties. EUV spectroscopy was continued outside of the institute during eight years. This area of work was supported again by the institute developing the Auto-Calibrating Spectrometers (SolACES) for a mission on the International Space Station (ISS). After more than six years in space the instrument is still in operation. Meanwhile the work on the primary task also to validate EUV data available from other space missions has made good progress. The first results of validating those data and combine them into one set of EUV solar spectral irradiance are very promising. It will be recommended for using it by the science and application community. Moreover, a new low-cost type of an EUV spectrometer is presented for monitoring the solar EUV radiation. It shall be further developed for providing EUV-TEC data to be applied in ionospheric models replacing the Covington index F10.7. Applying these data for example in the GNSS signal evaluation a more accurate determination of GNSS receiver positions is expected for correcting the propagation delays of navigation signals traveling through the ionosphere from space to earth. - Latest results in the field of solar EUV spectroscopy are discussed, too. [ABSTRACT FROM AUTHOR]

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 15ms-1 at 91 km height. Phase differences are slightly higher than 90°, which indicates a polarization that is nearly circular. On an average the QTDWis 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. [ABSTRACT FROM AUTHOR]

Average meteor heights have been continuously observed using a SKiYMET VHF radar at Collm (51.3° N, 13.0° E) since late summer of 2004. Initially, the daily mean meteor height was about 89.4 km. Since that time, average meteor heights have decreased. This is consistent with earlier results on middle atmosphere temperature change from the literature and from earlier results of low-frequency reflection height changes measured at Kühlungsborn and Collm. During the recent solar minimum 2008/2009 the meteor heights further decreased. Linear fitting of a trend and a solar cycle to the heights reveals a linear decrease of about -56myear-1 and a solar cycle effect of +450m per 100 sfu. Assuming that meteor heights, on a long-term average, approximately refer to a level of constant pressure, this decrease can be converted to a mean middle atmosphere linear temperature decrease of -0.23Kyear-1 and a solar cycle effect of +1.8K per 100 sfu during the last decade, which is in the range of observed trends reported in the literature. [ABSTRACT FROM AUTHOR]

The recent solar minimum has been characterized by an anomalous strong decrease of thermospheric density since 2005. Here we analyze anomalies of mesosphere/lower thermosphere parameters possibly connected with this effect. In particular, nighttime mean LF reflection heights measured at Collm, Germany, show a very strong decrease after 2005, indicating a density decrease. This decrease is also visible in mean meteor heights measured with VHF meteor radar at Collm. This density decrease is accompanied by an increase of gravity wave (GW) amplitudes in the upper mesosphere and a decrease in the lower thermosphere. On the decadal scale, GWs are negatively correlated with the background zonal wind, but this correlation is modulated in the course of the solar cycle, indicating the combined effect of GW filtering and density decrease. [ABSTRACT FROM AUTHOR]