15th Conference on Boundary Layer and Turbulence


A simple and general subgrid model suitable both for surface layer and free-stream turbulence

J.-L. Redelsperger, CNRM, Toulouse, France; and P. Carlotti and F. Mahé

A new and general approach is presented to allow standard subgrid schemes to be suitable both for surface layer and free-stream turbulence. Simple modifications to subgrid schemes are proposed and derived for any vertical stability conditions. They are simple to implement in models and are suitable for more complicated simulations such as LES with inhomogeneous surface conditions or complex topography. They are also applicable to mesoscale and large-scale models.

These modifications are physically justified by recent measurements of spectra close to the ground. The spectral analysis presented shows how the energy deficit of blocked turbulence for a given dissipation ('anomalous dissipation') dramatically effects on the coefficients to be used in subgrid schemes through new mixing and dissipative lengths.

As shown on neutral and convective cases with wind shear, these changes allow us to substantially improve the prediction of profiles for the mean quantities in the surface layer.

extended abstract  Extended Abstract (164K)

Session 13, Atmospheric Boundary Layer Parameterizations from Mesoscale to Macroscale
Thursday, 18 July 2002, 3:30 PM-5:30 PM

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