Influence of model resolution on short-range wind predictions in complex terrain

The Advanced Research WRF (ARW) model has been used in short-range simulations to explore the sensitivity of model physics and horizontal grid resolution. The ARW is a non-hydrostatic and fully compressible code. It uses the sigma-pressure coordinate in the vertical direction to better simulate airflow over complex terrain. The model solves the governing equations in flux-form, which enables conservation of mass and scalar quantities. The model physics contains cumulus convection, microphysics of cloud processes and precipitation, long- and short-wave radiation transfer, turbulence and diffusion, PBL, surface layer, and soil layer modules. There are a variety of choices for each of the physical processes. We have chosen several events during 2011 to study the impact of different grids and physics on low-level wind forecast for three wind farms, located in Southern Italy in a complex terrain environment. Short-range simulations are performed in three horizontally nested domains with resolutions of 8, 2.67, and 0.89 km to gauge the impact of model grid resolution on wind speed and wind energy forecast over complex terrain. All short-range WRF simulations last for 36 hours. Short-range simulations are validated with field measurements obtained by tower measurements in each site. Preliminary results indicate that the forecast error seems to exhibit little dependence on grid resolution and is relatively independent of physics configuration, while it is much more dependent on initial and boundary conditions. Results also suggest that the modelled winds generally seem to be most accurate for simulation scenarios associated with large scale strong pressure differences. Furthermore computational fluid dynamics simulations are in progress in a few case studies to model wind speed and direction using a topography resolutions of 90 m. These gridded wind simulations will be typically produced at resolutions of 100 m which is the mean distance among wind turbines.