Abstract
Abstract. While the wind farm parameterization by Fitch et al. (2012) in the Weather Research and Forecasting (WRF) model has been used and evaluated frequently, the explicit wake parameterization (EWP) by Volker et al. (2015) is less well explored. The openly available high-frequency flight measurements from Bärfuss et al. (2019a) provide an opportunity to directly compare the simulation results from the EWP and Fitch scheme with in situ measurements. In doing so, this study aims to complement the recent study by Siedersleben et al. (2020) by (1) comparing the EWP and Fitch schemes in terms of turbulent kinetic energy (TKE) and velocity deficit, together with FINO 1 measurements and synthetic aperture radar (SAR) data, and (2) exploring the interactions of the wind farm with low-level jets (LLJs). This is done using a bug-fixed WRF version that includes the correct TKE advection, following Archer et al. (2020). Both the Fitch and the EWP schemes can capture the mean wind field in the presence of the wind farm consistently and well. TKE in the EWP scheme is significantly underestimated, suggesting that an explicit turbine-induced TKE source should be included in addition to the implicit source from shear. The value of the correction factor for turbine-induced TKE generation in the Fitch scheme has a significant impact on the simulation results. The position of the LLJ nose and the shear beneath the jet nose are modified by the presence of wind farms.
Highlights
Offshore wind energy has been developing fast in recent years
With warmer air moving from land over the sea in the direction of about 240◦, a stable boundary layer (SBL) developed over the sea, as can be seen from the profile-flight data shown in Fig. 5a and c
The modeled potential temperature θ profiles consistently suggest the presence of the SBL, though the increasing of θ with height within the lowest 300 m is slightly smaller than the measurements
Summary
Offshore wind energy has been developing fast in recent years. wind farms are growing bigger and bigger in both capacity and spatial size. In the North Sea, a farm can extend over tens of kilometers and merge with neighboring farms, resulting in a cluster size of several thousand square kilometers, e.g., the Hornsea area (7240 km2); see 4Coffshore (2021) and Díaz and Guedes Soares (2020) for an overview of the current status of offshore wind farms. Wind turbines and farms extract momentum from the atmospheric flow and interact with it, causing reductions in wind speed and changes in turbulence in the wake regions. To assess such impacts over areas with sizes of modern farm clusters, mesoscale modeling has been shown to be a useful tool in including synoptical and mesoscale wind variability. In connection with the use of WRF, the wind farm parameterization (WFP) scheme (Fitch et al, 2012), called the Fitch scheme here, and the explicit wake parameterization (Volker et al, 2015), called the EWP scheme here, are the two most commonly applied explicit wind farm parame-
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