Assessment of Stability-Based Characterizations of North Carolina’s Offshore Wind Resource Using a Nested Boundary Layer Method

Abstract

SODAR wind profiler measurements from a land-based site within 1000 m of the coastal ocean are compared with predicted wind profiles based on upwind conditions and a stability-based model. The thermally dynamic influence of the Gulf Stream near the site of measurement, Cape Hatteras, has been found to complicate wind speed estimation at height through its impacts on atmospheric stability and the resulting changes to wind shear. The COARE 3.0 algorithm was used to calculate a Monin-Obukhov Similarity Theory (MOST) scaling parameter, quantifying the degree of stability of the marine environment as well as the friction velocity and roughness length. Knowledge of upwind conditions aided in estimating the height of nested roughness and thermal internal boundary layers (IBLs) to identify a range of the measured wind profile corresponding to winds over the water. This work suggests that MOST through COARE 3.0 provides a good estimate of wind-at-height behaviour, with some exceptions. The layers identified in the IBL approximations indicate that (1) effects of stability can improve wind speed estimation when upwind conditions are well defined, but (2) unexpectedly high levels of wind shear make this method unreliable within unstable layers above stable layers. These results impact the estimate of the available wind resource, as well as other properties applicable to wind energy engineering, including shear and turbulence characteristics.