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Description:
Turbulence in stable boundary layers (SBL) is often accompanied by the presence of large patches of non-turbulent flow regions, even close to the wall, a phenomenon referred in literature as global intermittency. Understanding the physical processes and dynamics of this mode of rotating, stratified and intermittent turbulence is important for the improvement of existing and/or development of new parametrizations of the SBL, which in turn, may be useful for many applications, including but not limited to numerical weather prediction, modeling gas dispersion events and understanding the Arctic climate system. In this thesis, the SBL is investigated by establishing a detailed comparison with the well-studied neutrally stratified atmospheric boundary layer. The datasets examined here were inherited through the work of Ansorge (Dissertation, Springer 2016). They used a simplified physical configuration, namely, an Ekman flow over a smooth wall where global intermittency is known to occur beyond a certain stability despite the absence of surface heterogeneities and other external perturbations. Comparisons between both regimes is accomplished with the help of coherent structures, particularly with their geometry. This is motivated from previous observations where a change in the geometry of these structures from hairpin vortices under neutral conditions to thermal plumes under unstable conditions (where there is a positive buoyancy flux) has been detected. However, very little is known about the geometry of these structures, especially their three-dimensional character, when buoyancy has a stabilizing effect. Since a well-accepted definition of a coherent structure has not yet surfaced, the classification of boundary layer structures introduced by Robinson (Dissertation, Stanford 1991), henceforth referred to as Robinson structures, is used to study the various structures identified in literature in an organized manner. Suitable scalar indicators are identified for all eight categories of Robinson structures and they ...