A North Sea in situ evaluation of the Fitch Wind Farm Parametrization within the Mellor–Yamada–Nakanishi–Niino and 3D Planetary Boundary Layer schemes

Abstract. Wind resource assessments and wind power forecasts that account for wind farm wakes are sensitive to the choice of planetary boundary layer (PBL) scheme. This work compares the one-dimensional Mellor–Yamada–Nakanishi–Niino (MYNN) PBL scheme with a three-dimensional PBL (3DPBL) scheme, evaluating predictions made with both schemes against two sets of North Sea in situ observations of wind farm wakes. The optimal PBL scheme varies based on the observations (FINO1 tower vs. aircraft), the quantity of interest (wind speed vs. turbulence kinetic energy [TKE]), and the error metric (bias, centered root mean square error [cRMSE], and R² vs. earth mover’s distance [EMD]). Whereas 3DPBL wind speeds outperform MYNN wind speeds with respect to the cRMSE at the FINO1 site within the turbine rotor layer, 3DPBL TKE bias underperforms MYNN TKE bias when compared to aircraft observations. Wind speeds in the aircraft region are ambiguous as to which PBL scheme is optimal. Aircraft MYNN wind speeds outperform 3DPBL wind speeds with respect to R² and cRMSE but underperform with respect to bias and EMD. Tests to determine the optimal wind farm TKE factor reveal similar variability: The aircraft observations support a wind farm TKE factor of 1 for MYNN cases and a wind farm TKE factor of 0 or 0.25 for 3DPBL cases. In contrast, the optimal wind farm TKE factor based on FINO1 observations differs by metric. For FINO1 wind speeds, the cRMSE suggests that a wind farm TKE factor of 0 is most appropriate, whereas the bias and EMD support a wind farm TKE factor of 1.