Modelling global offshore turbulence intensity including large-scale turbulence, stability and sea state

Abstract. This study delivers a method and datasets for a global offshore atlas for turbulence intensity (TI) from 10 m to 200 m. The method includes both surface driven, three dimensional boundary-layer turbulence, and large-scale two-dimensional turbulence. This systematically includes the effect of large scale eddies, particularly at weak wind conditions, and hence significantly improves TI in weak to moderate wind conditions. This method describes water roughness length through a dependence on wave age and wind speed, which is suitable for moderate to strong wind conditions. The method also includes stability dependence through the Obukhov length. Based on theories and measurements in literature, algorithms for TI have been calibrated for heights up to 200 m. We use the ERA5 atmospheric and wave data to demonstrate the use of the method and create a global dataset. The results show satisfactory agreement with measurements and data from the literature.