High resolution numerical modeling of the atmospheric circulation over complex terrain

A detailed knowledge of the atmospheric circulation which characterizes the complex Planetary Boundary Layers (PBLs) typical of mountainous regions is of great interest for environmental assessment studies. Furthermore, efforts are underway in developing wind farms, often located in mountainous areas; efficient wind power-plants require detailed and reliable knowledge of wind fluctuations near the surface which cannot be learned from regional-scale investigations. The Large Eddy Simulation (LES) methodology provides three-dimensional, time evolving structure of turbulence and a much more accurate estimate of turbulence statistics compared to those from PBL schemes used by operative meteorological models. In the present work the coherent structures and the turbulent characteristics of a complex PBL driven by surface heating, thermally-induced circulations and geostrophic wind forcing is investigated by means of the LES technique. The three-dimensional non-hydrostatic meteorological model WRF is used with a LES grid resolution to explicitly resolve the energy-containing turbulent eddies and is modified to include a new formulation for the filter width of the subgrid scale model. The LES model is coupled with a wall scheme and surface heat and momentum fluxes are computed based on Monin-Obukhov surface similarity theory.