Nonhydrostatic atmospheric cut cell model on a block-structured Cartesian mesh
Seminar Room 1, Newton Institute
AbstractOne of the most pressing concerns of next-generation atmospheric modeling is the handling of highly-resolved complex topography. Since an increase in horizontal resolution introduces steep slopes over mountainous areas, this leads to the conventional terrain-following models suffering from large truncation errors, hence they are no longer considered accurate enough for future high resolution models. 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 high resolution and highly-precise simulations over steep topography. Small cells cut by topography are combined with neighboring cells either vertically or horizontally to avoid severe restrictions on time steps due to the CFL condition. In addition, a block-structured mesh approach is introduced to achieve computationally efficient Cartesian grid simulations with both high vertical resolution near the ground and reasonable conservation characteristics.
This model successfully reproduces flows over not only a gently sloping bell-shaped mountain but also a semicircular mountain where significant errors are observed in a terrain-following model. It also reproduces a smooth and accurate mountain wave on a locally refined mesh around the semicircular mountain. This result agrees well with that using a uniformly fine mesh despite of its substantially low computational cost, thereby demonstrating the advantage of the model to simulate flows over steep topography.