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

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 compressi...

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Bibliographic Details
Published in:Geoscientific Model Development 2015-10, Vol.8 (10), p.3393-3419
Main Authors: Nishizawa, S, Yashiro, H, Sato, Y, Miyamoto, Y, Tomita, H
Format: Article
Language:English
Subjects:
Analysis
Aspect ratio
Boundary layer turbulence
Boundary layers
Compressibility
Computer simulation
Dye dispersion
Eddy viscosity
Energy
Energy spectra
Influence
Large eddy simulation
Large eddy simulations
Length
Mathematical models
Mixing length
Modelling
Numerical schemes
Oceanic eddies
Parameter sensitivity
Piles
Planetary boundary layer
Skewness
Slopes
Spatial discrimination
Spatial resolution
Statistical methods
Turbulence
Turbulence (Fluid dynamics)
Vertical velocities
Viscosity
Vortices
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Summary: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.
ISSN:1991-9603
1991-959X
1991-962X
1991-9603
1991-962X
DOI:10.5194/gmd-8-3393-2015