### 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.

Original language | English |
---|---|

Pages (from-to) | 3393-3419 |

Number of pages | 27 |

Journal | Geoscientific Model Development |

Volume | 8 |

Issue number | 10 |

DOIs | |

Publication status | Published - 2015 Oct 28 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Modelling and Simulation
- Earth and Planetary Sciences(all)

### Cite this

*Geoscientific Model Development*,

*8*(10), 3393-3419. https://doi.org/10.5194/gmd-8-3393-2015

**Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations.** / Nishizawa, S.; Yashiro, H.; Sato, Y.; Miyamoto, Yoshiaki; Tomita, H.

Research output: Contribution to journal › Article

*Geoscientific Model Development*, vol. 8, no. 10, pp. 3393-3419. https://doi.org/10.5194/gmd-8-3393-2015

}

TY - JOUR

T1 - Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations

AU - Nishizawa, S.

AU - Yashiro, H.

AU - Sato, Y.

AU - Miyamoto, Yoshiaki

AU - Tomita, H.

PY - 2015/10/28

Y1 - 2015/10/28

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=84946011609&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84946011609&partnerID=8YFLogxK

U2 - 10.5194/gmd-8-3393-2015

DO - 10.5194/gmd-8-3393-2015

M3 - Article

AN - SCOPUS:84946011609

VL - 8

SP - 3393

EP - 3419

JO - Geoscientific Model Development

JF - Geoscientific Model Development

SN - 1991-959X

IS - 10

ER -