Grey-Zone Turbulence in the Neutral Atmospheric Boundary Layer

• Published in: Boundary-layer meteorology Vol. 170; no. 2; pp. 191 - 204
• Main Author: Honnert, Rachel
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.02.2019; Springer; Springer Nature B.V; Springer Verlag
• Subjects: Atmospheric boundary layer; Atmospheric conditions; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Atmospheric turbulence; Boundary layer height; Boundary layers; Computer simulation; diagnostic techniques; Earth and Environmental Science; Earth Sciences; Fluxes; Geostrophic wind; Geostrophic winds; Granulation; isotropy; Kinetic energy; Large eddy simulation; Large eddy simulations; Meteorology; Momentum; Oceanic eddies; Partitioning; Planetary boundary layer; Procedures; Research Article; Resolution; Sciences of the Universe; simulation models; troposphere; Turbulence; turbulent flow; Turbulent kinetic energy; Wind shear; Wind speed; Winds; Zoning law; Grey-zone turbulence; Large-eddy simulation; Neutral boundary layer
• ISSN: 0006-8314; 1573-1472
• DOI: 10.1007/s10546-018-0394-y

The turbulence generated by wind shear is described at grey-zone resolutions using a theoretical neutral boundary layer based on atmospheric conditions constructed from measurements from the CASES-99 field campaign. Six-metre-resolution large-eddy simulations (LES) are performed to access the “true” resolved turbulence for two cases, corresponding to a forcing of the boundary layer by zonal geostrophic wind speeds of 10 m s - 1 and 20 m s - 1 . The LES fields are subject to a coarse-graining procedure in order to compute turbulence diagnostics in the grey zone, with the robustness and weakness of various averaging procedures tested, for which simple top-hat averaging is found to be both suitable and accurate. In addition, the “true” resolved and subgrid-scale fluxes, variances, turbulent kinetic energy and production terms are quantified on various scales. The grey zone of turbulence is defined as the range of scales where 10–90% of turbulence is resolved, which here ranges from resolutions of 25– 800 m ( 0.03 < Δ x / h < 1 , where Δ x is the horizontal resolution, and h is the boundary-layer height). The subgrid/resolved partitioning of the variances of the velocity components depends on the geostrophic wind speed, which is not the case for the momentum-flux partitioning. Dynamic production terms show that fine-scale turbulence is isotropic ( Δ x / h < 0.03 ) and is quasi one-directional, oriented in the direction of the geostrophic wind vector at the mesoscale ( Δ x / h > 1 ). The turbulence parametrizations, which are tested in the Méso-NH model by running simulations at resolutions from the LES scale to the mesoscale, fail to produce the correct turbulence regardless of resolution.