The horizontal winds in the mesosphere and lower thermosphere (MLT) at heights of about 80-100 km have been measured by the SKiYMET meteor radar at Collm, Germany (51.3°N, 13°E). The radar has been operating continuously since July 2004, and the data from December 2004 – December 2009 were used for constructing a climatology of the 8-h tide. The 8-h tide appears to be a regular feature in the MLT. In particular, the amplitude shows a clear seasonal behaviour, with maximum values around the equinoxes, and generally an increase with height. The largest amplitudes occur in autumn, sometimes reaching values above 15 m/s, but they are significantly smaller during summer (~1 m/s). The phase is early in winter and advances to later times in summer. In general, the phase difference between the zonal and meridional components is close to +2 h. The vertical wavelengths are short in summer (~30 km) but significant longer during the rest of the year. The results were compared with observations from locations of different latitudes.

Numerical resultsof the Middle and Upper Atmoshere Model (MUAM) for simulating the middle atmosphere conditions during January-February 2006 and 2008 have been compared wirth SABER/TIMED satellite data.

The 2009 solar minimum 23/24 has been characterized by an anomalous strong decrease in thermospheric density. We analyze anomalies of mesosphere/lower thermosphere parameters possibly connected with this effect. Nighttime mean low-frequency 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 a VHF meteor radar at Collm. It is accompanied by an increase/ decrease of gravity wave (GW) amplitudes in the upper mesosphere/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.

Absorption of radiation by atmospheric gases is characterised by specific line transition structures. Spectrally high-resolved line-by-line (lbl) spectra of the respective optical depths may vary over several orders of magnitude. To avoid time-consuming lbl simulations spectral averaging is commonly applied to obtain an averaged layer optical depth as a basis for fine- and broad-band absorption parameterisations for input in band radiative transfer models. It is shown that various averaging approaches can be applied but leading to significantly differing optical depth spectra whereby the usually considered method of averaging the layer transmissivity results in strong overestimations..

For a long period of time the need for power in Germany has mainly been and is still covered by coal as a very important resource. To extract the coal, some big holes in the surface were dug. After ending of the coal mining, they were filled with water in order to use them effectively, so anthropogenic lakes will be created. By 2050 the water surface area in the south of Leipzig will be enlarged to 6000 ha as a consequence of human intervention (Berkner, 2003). Due to the changed soil surface, there will be generate a change in the interaction between the atmosphere and the earth. In this article an approach is demonstrated to classify the effects of anthropogenic lakes with help of a mesoscale model.

To quantify the energy balance above a lysimeter without disturbance of the measured air volume itself, the applicability of an acoustic-meteorological measurement method is numerically investigated. Several sound paths between transmitters and receivers around the lysimeter border an air volume (‚acoustic chamber’) to determine the interaction between the ground surface and the environment with remote sensing. This study is focused on the sensitivity of the acoustically derived air temperature and wind vector values. To describe the uncertainty of these quantities outgoing from the uncertainty of the acoustic travel time, several effects on the sound propagation, e.g. air absorption, ground reflection, and atmospheric refraction are studied. Based on the wind and temperature data at several height levels, momentum and heat fluxes can be derived which are important for the energy exchange above the lysimeter surface. First results of the achievable accuracy for the fluxes are summarized in the study using a numerical model of the atmospheric boundary layer.

Cirrus clouds play an important role in atmospheric chemistry and climate, but they are complicated to handle mostly due to the complex non-spherical shape of the particles and their spatial inhomogeneity which causes major problems in remote sensing of cirrus from satellite platforms. Therefore spectral measurements of solar radiation are applied on the new research aircraft for atmospheric research and earth observation of the german science community HALO (High Altitude and LOng range research aircraft).

The Middle and Upper Atmosphere Model has been used to simulate the middle atmosphere variability by changing the lower boundary conditions. For this purpose quasi steady-state simulations were performed for individual days around the sudden stratospheric warmings (SSWs) in January 2009 and 2012. The modelled time series reveal a qualitatively good agreement with reanalysis zonal wind with the observed one by reanalysis at the same height and latitude. A medium-range prediction of SSW events appears possible if planetary waves (PW) in the lower stratosphere are additionally assimilated in form of externally forced travelling PW.

Sporadic E (Es) layer occurrence rates derived from GPS radio occultation measurements during the Geminid meteor showers 2006-2010 are compared with meteor rates obtained with the Collm VHF meteor radar. In most years, Es rates increase after the shower, with a short delay of few days. This indicates a possible link between meteor influx and the production of metallic ions that may form Es. However, the correlation between Es rates and meteor flux varies from year to year, indicating that more processes significantly influence Es occurrence also during meteor showers.

Measurement of aeolian sand transport rates with high temporal and spatial resolution is crucial for further progress in developing proper sand transport equations, in testing and developing numerical models of sand movement by wind, and in the modelling of sand dunes, ripples and other aeolian forms. Observational research on the behaviour of sand grains in natural sediments under natural conditions is presented herein. This study uses the established measuring principle of a Saltiphone (Spaan and Van den Abeele, 1991) and a webcam commonly used in personal computers. The webcam frame transfer is triggered every 0.1s by a sonic anemometer. Consecutive frames are compared and analysed in real-time by a computer program. The webcam signal also provides the number of moving grains also the grain size of the moving grains and this for every grain that has moved in a time step of 0.1s. Problems to determine the transport near the thresholds and the difficulties in the determination of thresholds from measured mean transport rates are discussed, and proposals for dealing with the problems are made. An iterative technique to determine the thresholds of transport (ITT) from high resolution transport measurements is presented. In this way, constitutive equations for sand transport in terms of wind speed can be tested. If viable, they can be employed to infer estimates for the thresholds by minimising the root-mean-square error between measured and calculated transport data. Alternatively, the fluid and impact thresholds for aeolian sand transport are determined from the field measurements on a beach by analysing the onset and breakdown of saltation in gust and lull intervals (GLM) of rising and falling wind speeds, respectively