Abstract
Abstract. In this work, the fully compressible, three-dimensional, nonhydrostatic atmospheric model called All Scale Atmospheric Model (ASAM) is presented. A cut cell approach is used to include obstacles and orography into the Cartesian grid. Discretization is realized by a mixture of finite differences and finite volumes and a state limiting is applied. Necessary shifting and interpolation techniques are outlined. The method can be generalized to any other orthogonal grids, e.g., a lat–long grid. A linear implicit Rosenbrock time integration scheme ensures numerical stability in the presence of fast sound waves and around small cells. Analyses of five two-dimensional benchmark test cases from the literature are carried out to show that the described method produces meaningful results with respect to conservation properties and model accuracy. The test cases are partly modified in a way that the flow field or scalars interact with cut cells. To make the model applicable for atmospheric problems, physical parameterizations like a Smagorinsky subgrid-scale model, a two-moment bulk microphysics scheme, and precipitation and surface fluxes using a sophisticated multi-layer soil model are implemented and described. Results of an idealized three-dimensional simulation are shown, where the flow field around an idealized mountain with subsequent gravity wave generation, latent heat release, orographic clouds and precipitation are modeled.
Highlights
In this paper we present the numerical solver ASAM (All Scale Atmospheric Model) that has been developed at the Leibniz Institute for Tropospheric Research (TROPOS), Leipzig
For simulating the flow around obstacles, buildings or orography, the cut cell approach is used. With this attempt one remains within the Cartesian grid and the numerical pressure derivative in the vicinity of a structure is zero if the cut cell geometry is not taken into account, which is not the case in terrain-following coordinate systems due to the slope of the lowest cells (Lock et al, 2012)
Cell 5 method, which is used in split-explicit time integration methods in the Weather Research and Forecasting (WRF) Model (Skamarock et al, 2008) or in the Consortium for Smallscale Modeling (COSMO) model (Doms et al, 2011)
Summary
For simulating the flow around obstacles, buildings or orography, the cut (or shaved) cell approach is used With this attempt one remains within the Cartesian grid and the numerical pressure derivative in the vicinity of a structure is zero if the cut cell geometry is not taken into account, which is not the case in terrain-following coordinate systems due to the slope of the lowest cells (Lock et al, 2012). Yamazaki and Satomura (2008) simulated a two-dimensional flow over different mountain slopes and compared the results of their cut cell model with a model using terrain-following coordinates. In ASAM, a linear-implicit Rosenbrock time integration scheme is used (Hairer and Wanner, 1996) Another option to handle the small cells problem is to merge small cut cells with neighboring cells in either the horizontal or vertical direction (Yamazaki and Satomura, 2010). Concluding remarks and future work are in the final section
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