Robust and accurate simulations of flows over orography using non-conforming meshes

Abstract: We systematically validate the static local mesh refinement capabilities of a recently proposed IMEX-DG scheme implemented in the framework of the deal.II library. Non-conforming meshes are employed in atmospheric flow simulations to increase the resolution around complex orography. A number of numerical experiments based on classical benchmarks with idealized as well as real orography profiles demonstrate that simulations with the refined mesh are stable for long lead times and no spurious effects arise at the interfaces of mesh regions with different resolutions. Moreover, correct values of the momentum flux are retrieved and the correct large-scale orographic response is established. Hence, large-scale orography-driven flow features can be simulated without loss of accuracy using a much lower total amount of degrees of freedom. In a context of spatial resolutions approaching the hectometric scale in numerical weather prediction models, these results support the use of locally refined, non-conforming meshes as a reliable and effective tool to greatly reduce the dependence of atmospheric models on orographic wave drag parametrizations.