Can we yet do a fairer and more complete validation of wind farm parametrizations in the WRF model?

Abstract

Wind-farm parametrizations in numerical weather prediction models continue to be developed and used to study the impact of wind farms on both the local climate and other wind farms. Therefore, it is important to evaluate their accuracy in simulating the wind field. Here, we evaluate the Fitch scheme, which is the in-built wind-farm parametrization of the Weather Research and Forecasting (WRF) model by simulating a small wind farm through idealized simulations in the WRF model. We simulate the wind-farm impact on the atmosphere by using two planetary boundary layer schemes, one of these designed for the terra incognita, a range of scales finer than used for traditional mesoscale simulations, yet still too coarse for large-eddy simulation (LES). For both schemes, we use two horizontal grid spacings, 960 and 240 m, which are typical within the terra incognita. We compare these simulations using the Fitch wind farm parametrization with wakes modelled at high-resolution using the LES capability of the WRF model combined with an actuator disk wind turbine model designed for LES. From this preliminary assessment, we find that the simulations at the coarsest resolution are in better agreement with spatially-averaged outputs of the LES compared to that of the medium-range resolution simulations with LES, which are spatially averaged to the medium size spacing. The medium-range resolution simulations show the greatest velocity differences between the simulations without and with wakes.