Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
Geosci. Model Dev., 8, 3393-3419, 2015
https://doi.org/10.5194/gmd-8-3393-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Development and technical paper
28 Oct 2015
Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations
S. Nishizawa, H. Yashiro, Y. Sato, Y. Miyamoto, and H. Tomita RIKEN Advanced Institute for Computational Science, Kobe, Japan
Abstract. We examine the influence of the grid aspect ratio of horizontal to vertical grid spacing on turbulence in the planetary boundary layer (PBL) in a large-eddy simulation (LES). In order to clarify and distinguish them from other artificial effects caused by numerical schemes, we used a fully compressible meteorological LES model with a fully explicit scheme of temporal integration. The influences are investigated with a series of sensitivity tests with parameter sweeps of spatial resolution and grid aspect ratio. We confirmed that the mixing length of the eddy viscosity and diffusion due to sub-grid-scale turbulence plays an essential role in reproducing the theoretical −5/3 slope of the energy spectrum. If we define the filter length in LES modeling based on consideration of the numerical scheme, and introduce a corrective factor for the grid aspect ratio into the mixing length, the theoretical slope of the energy spectrum can be obtained; otherwise, spurious energy piling appears at high wave numbers. We also found that the grid aspect ratio has influence on the turbulent statistics, especially the skewness of the vertical velocity near the top of the PBL, which becomes spuriously large with large aspect ratio, even if a reasonable spectrum is obtained.

Citation: Nishizawa, S., Yashiro, H., Sato, Y., Miyamoto, Y., and Tomita, H.: Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations, Geosci. Model Dev., 8, 3393-3419, https://doi.org/10.5194/gmd-8-3393-2015, 2015.
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Short summary
The influence of the large grid aspect ratio of horizontal to vertical grid spacing traditionally used in meteorological large-eddy simulations on simulated turbulence is investigated with a series of sensitivity tests with various grid configurations. We confirmed that the grid aspect ratio should be taken into account in the sub-grid scale model to reproduce the theoretical energy spectrum. We also found that the grid aspect ratio has an influence on the turbulent statistics.
The influence of the large grid aspect ratio of horizontal to vertical grid spacing...
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