High-resolution simulation of the evening transition in the atmospheric boundary layer with the spectral element method

Numerical simulation of the diurnal cycle in the atmospheric boundary layer is challenging due to the large range of scales present in the turbulent flow. The daytime boundary layer requires a large domain to capture the largest turbulent structures, while the small, stratified structures in the nighttime boundary layer require a high resolution. High-resolution simulation of the full diurnal cycle therefore requires efficient use of computational resources. We are using a newly developed large eddy simulation framework based on the highly parallelizable spectral element method to effectively leverage the currently available resources for this type of demanding simulations. The spectral element method makes it possible to run very large simulations on large compute clusters, and it is highly suitable for use on GPUs. As a first step toward simulation of the full diurnal cycle, we will present results from a large eddy simulation of the evening transition and growth of the stable layer into a layer of residual turbulence. The simulation is based on observations from the CASES99 field campaign. This high-resolution simulation of the evening transition will allow us to study coherent structures that form during the transition phase and have previously not been captured in detail. The data may also provide a better understanding of the role that entrainment may play in the growth of the stable nighttime boundary layer.