A North Sea Climatology of Anomalous Wind Events

Uncertainty reduction in offshore wind systems heavily relies on meteorological advances. A detailed characterization of the wind climate at a given site is indispensable for site assessment, and its accurate representation in load assessment models can reduce costs of turbine design and the risk of failure. While regular wind conditions are reasonably described by established methods, some atypical wind conditions are poorly understood and represented, although they contribute substantially to loads on turbines. In this study, 4 years of high-quality observations gathered up to 300 m were analyzed to characterize the wind climate at Met Mast IJmuiden, focusing on these ill-defined conditions. Following a systematic approach, six ‘anomalous wind events’ were identified and described: low-level jets, extreme wind speeds, shear, veer, turbulence and wind ramps. In addition, we identified typical weather conditions that favor their formation. The poster illustrates the definition and characterization of three of these events. It is shown that low-level jets occur predominantly in spring and summer, when relatively cold sea water leads to the formation of stable layers near the surface. Extreme shear is most likely for southwesterly flows associated with the passage of cyclones. Typical wind ramps in a one-hour time window are in the order of 2 m/s, and we show how our ramp-criterion can be used for e.g. resource assessment. It is not straightforward to incorporate anomalous wind events in traditional practices for e.g. load assessment, i.e. a bottom-up approach based on idealized, theoretical description of the wind field. However, our results suggest that downscaling studies based on a top-down clustering approach with well-chosen parameters will naturally encompass these anomalous wind events.

Relevant publication: https://doi.org/10.1016/j.jweia.2017.03.008