Evaluating winds and vertical wind shear from Weather Research and Forecasting model forecasts using seven planetary boundary layer schemes

Abstract

The existence of vertical wind shear in the atmosphere close to the ground requires that wind resource assessment and prediction with numerical weather prediction (NWP) models use wind forecasts at levels within the full rotor span of modern large wind turbines. The performance of NWP models regarding wind energy at these levels partly depends on the formulation and implementation of planetary boundary layer (PBL) parameterizations in these models. This study evaluates wind speeds and vertical wind shears simulated by the Weather Research and Forecasting model using seven sets of simulations with different PBL parameterizations at one coastal site over western Denmark. The evaluation focuses on determining which PBL parameterization performs best for wind energy forecasting, and presenting a validation methodology that takes into account wind speed at different heights.Winds speeds at heights ranging from 10 to 160 m, wind shears, temperatures and surface turbulent fluxes from seven sets of hindcasts are evaluated against observations at Høvsøre, Denmark. The ability of these hindcast sets to simulate mean wind speeds, wind shear, and their time variability strongly depends on atmospheric static stability. Wind speed hindcasts using the Yonsei University PBL scheme compared best with observations during unstable atmospheric conditions, whereas the Asymmetric Convective Model version 2 PBL scheme did so during near-stable and neutral conditions, and the Mellor-Yamada-Janjic PBL scheme prevailed during stable and very stable conditions. The evaluation of the simulated wind speed errors and how these vary with height clearly indicates that for wind power forecasting and wind resource assessment, validation against 10 m wind speeds alone is not sufficient. Evaluation of wind shear in the WRF model C. Draxl et al.the overall power losses by a wind farm. Furthermore, when the output from mesoscale models is used for wind resource assessment, information about the wind profile across the rotor area will lead to more accurate resource estimates.Because the grid resolution in mesoscale numerical weather prediction (NWP) models is too large to explicitly resolve the processes responsible for small-scale fluxes in the planetary boundary layer (PBL), sub-grid-scale turbulent fluxes, which are mostly unknown, and vertical mixing are calculated by PBL parameterizations. 4 PBL parameterizations use the distribution of wind, temperature, and water vapor mixing ratio with height and the surface fluxes calculated from a land surface model (LSM) and/or surface layer scheme to determine, amongst many others, the time tendencies of wind, temperature and water vapor mixing ratio. The choice of PBL scheme thus plays a significant role in the evolution of the low-level wind structure and therefore can heavily impact the quality of the forecast winds.Many aspects of the mesoscale model determine the quality of the forecast PBL structure. In the Weather Research and Forecasting (WRF) model, surface momentum, heat and moisture fluxes are c...

Hub Height Ocean Winds over the North Sea Observed by the NORSEWInD Lidar Array: Measuring Techniques, Quality Control and Data Management

“…Therefore, there was a need to compare the model results with observations on places where the wind resource at such levels had never been measured. Although most wind resource assessment software, such as the Wind Atlas Analysis and Application Program (WAsP) [29], estimate the wind turbine/farm energy production based on wind speed distributions at hub height and with that respect the outputs of a mesoscale model are rather good [30], the mesoscale models have shown difficulties to reproduce the wind profiles and, therefore, the vertical wind shear [31]. The latter becomes more important for wind turbines with large rotor areas as the difference between the below and above hub height winds might have a great impact on the loads and energy yield.…”

Ten Years of Boundary-Layer and Wind-Power Meteorology at Høvsøre, Denmark

“…see http://www.wasaproject.info). Wind speeds, temperatures and vertical wind shears simulated by the model were evaluated against Høvsøre measurements by Draxl et al (2014). Different PBL schemes were examined to determine which parametrization performs best for windenergy forecasting.…”

Sensitivity of the WRF model to PBL parametrisations and nesting techniques: evaluation of wind storms over complex terrain

“…Besides, they are used in the so-called hindcast simulations, which combine the reliability of reanalysis products with the high resolution provided by RCMs. Studies focusing specifically on wind have been one of the applications of such types of simulations (Jiménez et al, 2010;Jerez and Trigo, 2013;Etienne et al, 2013;García-Díez et al, 2013Menendez et al, 2014;Lorente-Plazas et al, 2015;Draxl et al, 2014).…”