Articles | Volume 8, issue 2
Model description paper
18 Feb 2015
Model description paper |  | 18 Feb 2015

ASAM v2.7: a compressible atmospheric model with a Cartesian cut cell approach

M. Jähn, O. Knoth, M. König, and U. Vogelsberg

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.

Short summary
A detailed description of the All Scale Atmospheric Model (ASAM) is presented. To include obstacles or orographical structures within the Cartesian grid, the cut cell method is used. Discretization is realized by a mixture of finite differences and finite volumes together with a linear-implicit Rosenbrock time integration scheme. Results of idealized test cases are shown, which include conservation tests as well as convergence studies with respect to model accuracy.