The making of the New European Wind Atlas ¿ Part 1: Model sensitivity
This is the first of two papers that document the creation of the New European Wind Atlas (NEWA). It describes the sensitivity analysis and evaluation procedures that formed the basis for choosing the final setup of the mesoscale model simulations of the wind atlas. The suitable combination of model setup and parameterizations, bound by practical constraints, was found for simulating the climatology of the wind field at turbine-relevant heights with the Weather Research and Forecasting (WRF) model. Initial WRF model sensitivity experiments compared the wind climate generated by using two commonly used planetary boundary layer schemes and were carried out over several regions in Europe. They confirmed that the most significant differences in annual mean wind speed at 100 m a.g.l. (above ground level) mostly coincide with areas of high surface roughness length and not with the location of the domains or maximum wind speed. Then an ensemble of more than 50 simulations with different setups for a single year was carried out for one domain covering northern Europe for which tall mast observations were available. We varied many different parameters across the simulations, e.g. model version, forcing data, various physical parameterizations, and the size of the model domain. These simulations showed that although virtually every parameter change affects the results in some way, significant changes in the wind climate in the boundary layer are mostly due to using different physical parameterizations, especially the planetary boundary layer scheme, the representation of the land surface, and the prescribed surface roughness length. Also, the setup of the simulations, such as the integration length and the domain size, can considerably influence the results. We assessed the degree of similarity between winds simulated by the WRF ensemble members and the observations using a suite of metrics, including the Earth Mover¿s Distance (EMD), a statistic that measures the distance between two probability distributions. The EMD was used to diagnose the performance of each ensemble member using the full wind speed and direction distribution, which is essential for wind resource assessment. We identified the most realistic ensemble members to determine the most suitable configuration to be used in the final production run, which is fully described and evaluated in the second part of this study (Dörenkämper et al., 2020). ; The European Commission (EC) partly funded the NEWA project (New European Wind Atlas) through FP7 (topic FP7-ENERGY.2013.10.1.2) The authors of this paper acknowledge the support the Danish Energy Authority (EUDP 14-II, 64014-0590, Denmark); the German Federal Ministry for the Economic Affairs and Energy, on the basis of the decision by the German Bundestag (ref. no. 0325832A/B); Latvijas Zinatnu Akademija (Latvia); Ministerio de Economía y Competitividad (Spain, ref. nos. PCIN-2014-017-C07-03, PCIN-2016-176, PCIN-2014-017-C07-04, and PCIN-2016-009); the Swedish Energy Agency (Sweden); and the Scientific and Technological Research Council of Turkey (grant no. 215M386). Andrea N. Hahmann additionally acknowledges the support of the Danish Ministry of Foreign Affairs, administered by the Danida Fellowship Centre under the project "Multiscale and Model-Chain Evaluation of Wind Atlases" (MEWA) and the ForskEL/EUDP (Denmark) project OffshoreWake (PSO-12521, EUDP 64017-0017).