Daniel Steppich «  Sabine Wüst »  Silviu Grecu
Sabine Wüst
Wechselwirkungen zwischen atmosphärischen Schwerewellen, planetaren Wellen und dem Grundstrom während der DYANA-Kampagne
Betreuer: PD Dr. Michael Bittner [Experimentalphysik II]
Datum der mündlichen Prüfung: 30.01.2009
172 Seiten, deutsch
Waves are of significant importance for the dynamical description of the atmosphere, especially of the middle atmosphere. They transport energy and momentum over a wide range and therefore, play a crucial role as a coupling mechanism between different atmospheric regions. Through interactions - either with the zonal mean flow or with other waves - energy is transferred. Understanding these interactions is necessary for our understanding of the atmosphere as well as for an adequate representation of waves in atmospheric and climate models. This work investigates interactions between gravity waves and the zonal mean flow (absorption and reflection), interactions between planetary waves among each other and effects of planetary waves on the natural variability of the atmosphere. The data used are based on measurements of meteorological rockets (chaff, falling spheres and datasondes) and ERA-40 analyses both covering the middle atmosphere. The vertically highly resolved temperature and wind rocket data originate from the DYANA campaign having taken place at Andoya (69%B0N, 16%B0E), Northern Norway and Biscarrosse (44%B0N, 1%B0W), Southern France between January and March 1990. ERA-40 data are needed for the spatial analysis of planetary waves. A combination of filtering and spectral analysis techniques is applied to the data. Furthermore, a non-linear approach is used for calculating energy dissipation rates of gravity waves above Biscarrosse. A comparison between this non-linear method and measured values is provided. Hints towards an atmospheric wave duct sensitive for small-scale gravity waves are found in the DYANA data above Biscarrosse. In a case study, one to two critical layers with elevated energy dissipation can be observed over a couple of hours. They are interpreted in terms of wave reflection taking into account the results of Wüst and Bittner (2006). The development of the critical layer for small-scale gravity waves above Andoya is studied in a time interval of about one month. A downward movement for about 17 days is observed and attributed to a changing wind field due to a stratospheric warming. Nearly in the same time interval indication for a resonant interaction between two travelling planetary waves with zonal wave number 2 or a travelling and a quasi-stationary one is found when combining DYANA and ERA-40 data above Andoya. Also, indication for a non-linear resonant interaction (triad) between two planetary waves 1 and one planetary wave 2 is given. At least, an analysis of regions of reduced atmospheric variability due to planetary waves or / and a diminished horizontal temperature gradient concludes the work. These regions are of enhanced importance for satellite validation but also for the discrimination of chemical and dynamical trends in the atmosphere.