Downscaling of Wind Resources From Mesoscale Tendencies with URANS

A mesoscale to microscale model chain that relates large scale wind climatologies with site conditions, for theprediction of wind resources and siting parameters, is under development within the New European Wind Atlas(NEWA) project. A statistical-dynamic downscaling method is proposed here based on the blending of long-term statistics of mesoscale forcings, extracted from the WRF mesoscale model, with site conditions simulatedwith unsteady k-ε Raynolds-Averaged Navier Stokes (URANS). The dynamic coupling of WRF and CFDWindhas been developed using the GABLS3 diurnal cycle benchmark in flat terrain. The coupling is done offline byfirst running the WRF model to obtain time series of mesoscale tendencies (pressure gradient and advectionterms) at a horizontal resolution of 3 km. Then, these tendencies are averaged temporally using a 1-hr rollingmean and spatially over a 3x3 grid at the site of interest to filter out small-scale forcings that will be explicitlymodelled at microscale. These tendencies are reduced to a cycle of input forcings for the microscale model tosimulate prevailing wind conditions. The methodology is tested at the;Cabauw 100-m mast in flat terrain.