Abstract

Synchronizing with the rapid development of computer technology, resolutions of atmospheric numerical models have increased significantly. One of the most pressing concerns of high-resolution atmospheric modeling is handling of steep slopes in mountainous areas. In this study, a cut cell method for representing topography on a Cartesian grid is applied to a two-dimensional nonhydrostatic atmospheric model to achieve highly-precise simulations over steep terrain. Small cells cut by topography are combined with neighboring cells either vertically or horizontally to avoid severe restrictions on time steps by the CFL condition. A unique staggered arrangement of variables used along with the cell-combining approach enables quite simple computations of momentum equations without the evaluation of surface pressure and reduces the computational cost of combining cells for the velocity variables (Yamazaki and Satomura 2010).

The results of two-dimensional numerical simulations of mountain waves using the developed model will be presented. The model successfully reproduces flows over a wide range of slopes from a gently sloping bell-shaped mountain to an extremely steep cliff with slopes over 80 degrees. A brief introduction of some recent developments will conclude the presentation.

References: Yamazaki, H. and T. Satomura, 2010: Nonhydrostatic atmospheric modeling using a combined Cartesian grid, Monthly Weather Review, 138, pp. 3932-3945, doi:10.1175/2010MWR3252.1