Assessing the dependence of surface layer atmospheric stability on measurement height at offshore locations

•Atmospheric stability is strongly dependent on meteorological measurement height.•Accuracy of Monin–Obukhov theory is strongly dependent on strict data filtering.•An atmospheric sub-layer in surface layer complicates wind profile extrapolation.

Incorporating atmospheric stability into wind resource assessment modelling is becoming more common. This study investigates some of the challenges associated with calculating stability in the offshore environment. Data are analysed from meteorological masts FINO1 and FINO3 in the German North Sea using measurements at three different heights and results show significant differences in stability assessment depending on which combination of heights is used. All methods show the North Sea to be very unstable for the majority of the time, although by ignoring wind and thermal data from below 50 m, the atmosphere appears more stable, indicating the presence of a marine internal boundary layer. Even 80 km out to sea, it is observed that FINO3 still feels the effects of land, and it is clear that the height of the atmospheric surface layer affects wind speed measurements under certain conditions.