The 236th R-CCS Cafe - part 3

Recent development of supercomputers will enable us to perform global atmospheric simulations with horizontal grid-spacing of O (10-100 m) near the future. In such spatial resolutions, large-scale eddies in the planetary boundary layer (PBL) can be explicitly resolved by Large-Eddy simulation (LES). However, the state-of-the-art atmospheric models often adopt low-order grid-point methods (e.g., totally second-order accuracy) for the fluid calculations. The numerical errors are possible to dominate the sub-grid scale effect by the turbulent models. To reveal numerical accuracy necessary for the advection terms, Kawai and Tomita (2021) derived numerical criteria and indicated that the seventh or eighth-order accuracy is required. To achieve such high-order accuracy, we recently focus on the discontinuous Galerkin method (DGM). Compared to the conventional grid-point methods, DGM has two advantages: the straightforward strategy for high-order discretization and easiness of computational compactness. To investigate the suitability of DGM for the atmospheric LES, we extended the numerical criteria to the DGM framework. Based on the numerical criteria, the required polynomial order is at least four. We verified this indication via an idealized numerical experiment of PBL turbulence using our developing LES model based on nodal DGM. In this talk, I will introduce the overview of this study.