The WRF model and the diurnal cycle of orographically-influenced flow: A case study

The Weather Research and Forecasting (WRF) model is widely used in modelling for wind energy purposes. Previous research indicated that under some situations, the WRF model fails to properly represent the diurnal cycle in wind speed. Here we present a case study with a North Sea jet where the WRF-simulated wind diurnal cycle is compared with observations at the Østerild tall mast in Northern Jutland, Denmark. The diurnal cycle in wind speed has different shapes at different heights and the WRF model can replicate the diurnal cycle at higher levels (∼250 m a.g.l.) but fails to replicate it near surface. We investigate the effect of using different Planetary Boundary Layer (PBL) and Surface Layer (SL) schemes and compare stability data between model and observations. The results suggest a weak link between the model's ability to replicate stability, probably linked to incorrect surface roughness length specification, and the model's ability to replicate diurnal cycle at lower levels.