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Grey-Zone Turbulence in the Neutral Atmospheric Boundary Layer

Abstract : 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 < x/h < 1, where x is the horizontal resolution, and h is the boundarylayer 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 (x/h < 0.03) and is quasi one-directional, oriented in the direction of the geostrophic wind vector at the mesoscale (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.
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https://hal-meteofrance.archives-ouvertes.fr/meteo-03357818
Contributor : Rachel Honnert Connect in order to contact the contributor
Submitted on : Wednesday, September 29, 2021 - 9:08:06 AM
Last modification on : Tuesday, October 19, 2021 - 7:01:42 PM

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Rachel Honnert. Grey-Zone Turbulence in the Neutral Atmospheric Boundary Layer. Boundary-Layer Meteorology, Springer Verlag, 2019, 170 (2), pp.191-204. ⟨10.1007/s10546-018-0394-y⟩. ⟨meteo-03357818⟩

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