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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

Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations