Cedrick Ansorge Livres

This thesis explores strong stratification and turbulence collapse in the planetary boundary layer, marking a significant advancement in the field. It uniquely examines all regimes of stratified turbulence within a unified simulation framework, avoiding breaks in turbulence representation paradigms. Previous progress in understanding and parameterizing turbulence in stable boundary layers has faced challenges due to difficulties in simulating strongly stratified regimes, relying mainly on field measurements. This work shifts that paradigm by showcasing how direct numerical simulation can effectively tackle these issues, eliminating uncertainties associated with turbulence models. Using a stably stratified Ekman layer as a simplified model, the study reproduces the three natural stratification regimes: weakly, intermediately, and strongly stratified, leveraging this data to address key, long-standing questions. The thesis is structured into three sections: a comprehensive introduction, numerics, and physics, culminating in a clear conclusion that highlights specific implications for stable boundary layer research. This organization prioritizes physical results while also addressing the technical aspects of numerical schemes and post-processing tools. The literature selection in the introduction effectively integrates insights from fluid dynamics and boundary-layer meteorology, enhancing the study's relevance.