This thesis presents a study of strong stratification and turbulence collapse in the planetary
boundary layer opening a new avenue in this field. It is the first work to study all regimes
of stratified turbulence in a unified simulation framework without a break in the paradigms for
representation of turbulence.To date advances in our understanding and the parameterization of
turbulence in the stable boundary layer have been hampered by difficulties simulating the
strongly stratified regime and the analysis has primarily been based on field measurements.
The content presented here changes that paradigm by demonstrating the ability of direct
numerical simulation to address this problem and by doing so to remove the uncertainty of
turbulence models from the analysis. Employing a stably stratified Ekman layer as a simplified
physical model of the stable boundary layer the three stratification regimes observed in
nature- weakly intermediately and strongly stratified-are reproduced and the data is
subsequently used to answer key long-standing questions.The main part of the book is organized
in three sections namely a comprehensive introduction numerics and physics. The thesis ends
with a clear and concise conclusion that distills specific implications for the study of the
stable boundary layer. This structure emphasizes the physical results but at the same time
gives relevance to the technical aspects of numerical schemes and post-processing tools. The
selection of the relevant literature during the introduction and its use along the work
appropriately combines literature from two research communities: fluid dynamics and
boundary-layer meteorology.
