Determine the effect of surface variability, filter scale, and position in the flow on subfilter-scale physics and their relation to coherent structures via wind tunnel measurements using particle image velocimetry.

Evaluate current and proposed SGS models for their ability to accurately predict the correct statistics and local flow behavior (i.e., coherent structures) around roughness transistions.

To contribute to the development of new SGS models for turbulence simulations by studying the relationship of subfilter-scale physics and resolved-scale coherent structures in the atmospheric surface layer using arrays of sonic anemometers.

To test, a priori, current and proposed SGS models for the ability to accurately reproduce the structure and statistics of the resolved scales directly resolved through high-resolution field measurements.

Preliminary results have shown that traditional eddy-viscosity parameters (Cs^2) vary locally in the presence of a surface roughness transition. Furthermore, traditional SGS models are shown to fail to produce correct boundary layer statistics. More advanced SGS models are currently being evaluated and adjustments to their formulations or new models will be proposed based on these studies.

Strong positive and negative subfilter-scale (or subgrid-scale) transfers of energy (and scalar variance) in the atmospheric surface layer have been shown to occur, seemingly, around the same inclined, hairpin-like coherent structures.

Different subgrid-scale turbulence models have been tested using high-resolution field data. The commonly used eddy-diffusion model yields subgrid-scale fluxes and dissipation whose statistics (mean values, pdfs) are significantly different from the statistics of measured subgrid-scale variables. New models based on scale-similarity arguments (e.g. similarity and non-linear models) are better able to reproduce the observations.

Carper, MA and Porté-Agel F, (2005) A-priori wind tunnel studies of subgrid-scale models for large-eddy simulations over rough-to-smooth surface transitions, to be presented at the EGU general assembly in Vienna, Austria.

Carper, M.A., and F Porté-Agel, (2004) The role of coherent structures on subfilter-scale dissipation rates of turbulence measured in the atmospheric boundary layer. Journal of Turbulence, 5 040. available here

Carper, MA, Porté-Agel F and Stoll R, (2003), A-priori laboratory studies to improve modeling of land-atmosphere interactions over heterogeneous surface conditions, Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract H42A-1064

Porté-Agel, F., Pahlow, M., Meneveau, C., Parlange, M.B., (2001), Atmospheric stability effect on subgrid-scale physics for large-eddy simulation, Advances in Water Ressources, vol. 24, 1085-1102. available here

Porté-Agel, F., Parlange, M.B., Meneveau, C., (2001), A priori field study of the subgrid-scale heat fluxes and dissipation in the atmospheric surface layer, Journal of Atmospheric Science, vol. 58(18), 2673-2698. available here