Turbulence in complex topographie : characterization of the site Terfens

Turbulence in complex topography is a topic which is still far from being understood completely. To gain further insights, several scientific studies were conducted over the past years. One of them is the, still ongoing, i-Box Project, a long-term study of boundary layer processes in highly complex terrain. This Master Thesis deals with the characterization of turbulence at a particular station of this project, named after the nearby village Terfens. The first aspect investigated is the influence of different coordinate rotation schemes on the turbulent fluxes. Therefore a double rotation (DR) procedure is compared to planar fit (PF) and sectoral planar fit (SPF) approaches. It is shown that a single plane PF approach is not sufficient to describe the turbulence accurately. For the heat flux and the friction velocity the differences between DR and SPF are negligible for the up-valley and down- valley winds. Regarding the slope winds, significant differences between all the rotation methods can be detected. The second part deals with the surroundings of the station. The roughness length and zero plane displacement height are calculated under near neutral conditions using a logarithmic wind profile approach. z0 yields a relatively high value of 0.58m and for d a significant direction dependence, most likely due to a steep embankment in the near vicinity of the measurement, can be found. In a third part the state of turbulence on the example of the sensible heat flux is investigated. Several valley wind days with similar conditions concerning the radiation and pressure gradients are chosen. An interaction of the heat flux with the valley wind system can be detected. Analyzing different diurnal cycles of w′′, which correspond to a different timing of the valley wind reversal, it is found that w′′ in a valley atmosphere, under thermally driven conditions, seems to be not only thermally, but also mechanically forced.by Markus EmprechtingerMasterarbeit, 2018(VLID)245281