LUDWIG
The atmosphere is characterized by a multitude of chemical, dynamic and radiative processes. In the LUDWIG project, dynamic processes (gravity waves) are being studied. These contribute to the distribution of energy in the atmosphere and — where they transmit this energy – influence the circulation. They arise, for example, when air masses encounter a mountain range like the Alps.
As part of this project, the NDMC (Network for the Detection of Mesospheric Change) is being expanded in the Alpine region by installation of the GRIPS (a spectrometer) and FAIM (a camera system) instruments at Sonnblick Observatory in Austria. Measurements there allow the derivation of spatial and temporal information on gravity waves at 80 – 90 km altitude. The Sonnblick time series, covering about two years, was assessed along with other NDMC Alpine data sets from four additional stations as to whether the gravity wave activity observed over the Alps can be considered homogenous, or reveals spatial or temporal variations.
The main project results were that the energy transported by gravity waves (the potential energy density) follows a clear annual cycle in the Alpine region. Compared with the NDMC station in the Lesser Caucasus the detected energy values in the Alpine regions are frequently lower. Short-period seasonal variation does not exist. This leads to the conclusion that the distribution or excitation mechanisms differ for these two oscillation periods. For the entire year, in the short-period range almost constant differences in potential energy densities can be observed between many stations, which could be attributed to local source or filter mechanisms.
The preferential direction of propagation for wavelengths around 60 km and less have a definite north-east component in summer and a south-west or west orientation in winter. This phenomenon can also be roughly observed worldwide at other locations, so it cannot be assessed as local. The reasons for this behaviour are only partially known. They are masked by local variations between Oberpfaffenhofen and Sonnblick.
In practice, the results can be used in the validation of climate and weather models. With the development of algorithms and climate models a foundation was laid in this project for continued, in some cases operational, assessment of NDMC data on energy transport or its direction of propagation, phase velocity, and horizontal wavelength, also after the end of the project.
The work in the LUDWIG project was funded by the Bavarian State Ministry of the Environment and Consumer Protection.
Funding code: TUS01UFS-67093.