The Making of the New European Wind Atlas, Part 1: Model Sensitivity

Abstract

Abstract. This is the first of two papers that documents 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. An optimal combination of model setup and parameterisations 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 largest differences in annual mean wind speed at 100 m 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. Many different parameters were varied across the simulations, for example, model version, forcing data, various physical parameterisations and the size of the model domain. These simulations showed that although virtually every parameter change affects the results in some way, significant changes on the wind climate in the boundary layer are mostly due to using different physical parameterisations, 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. The degree of similarity between winds simulated by the WRF ensemble members and the observations was assessed 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 distribution, which is important for wind resource assessment. The most realistic ensemble members were identified 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.

The Making of the New European Wind Atlas – Part 2: Production and Evaluation

“…the domain size). These aspects are discussed in more detail in the Part 1 paper of this study (Hahmann et al, 2020b). It is important to mention here that the data from the 291 mast used for evaluation were not used for the selection of the WRF model setup used in the NEWA production simulations.…”

“…The choice of the domain configuration is one of the most debatable aspects of the mesoscale setup. The choice of having each country (with exceptions, see Hahmann et al, 2020b) covered in one domain was in part motivated by the rationale that wind farm projects rarely cross borders and thus the points of interest for one wind farm should be in one domain only. This should avoid the confusion for the end user that could result if inconsistent time series, which originate from two different domains, are used within one project.…”

Europe's offshore winds assessed with synthetic aperture radar, ASCAT and WRF

“…The NOAH land surface model and icing WSM5 plus ice code and sum of cloud and ice humidity are used. The WRF simulations used three nested domains at 27, 9 and 3 km and 61 vertical layers, with 8 d overlapping runs using spectral nudging with 24 h spin-up (see Hahmann et al, 2020, for details on the technique). There are 20 model levels below 1 km, and the lowest levels are located at 5.6, 21.8, 40.4, 56.6, 72.8, 90.7, 113.2, 140.1, 170.7, 205.3 and 244.5 m above ground level.…”

“…The NEWA project (2015-2019) produced the novel stateof-the-art offshore wind atlas for European seas covering a minimum distance up to 100 km offshore and the entire North Sea and Baltic Sea, excluding Iceland. In addition to the entire wind atlas simulated using the Weather, Research and Forecasting (WRF) model (Hahmann et al, 2020), satellite synthetic aperture radar (SAR) and Advanced Scatterometer (ASCAT) ocean winds are also processed and analysed for wind resource assessment.…”

Review Tomaszewksi and Lunquist – GMD 2019-302

“…Major Comment: MYNN parametristaion changes: In the framework of the sensitivity studies that were conducted for the New European wind atlas different WRF versions were evaluated ([1] & [2]). From the analysis of theres results, a sensitivity towards different versions of the MYNN scheme was found.…”