Wind turbulence over surface waves under misaligned wind-wave conditions

The impact of sea state on air-sea momentum flux, or drag coefficient, is a poorly understood component of wind-wave interactions, particularly in high wind conditions. Wind stress and mean wind profile over the ocean are modulated by transient turbulent events, the occurrence and intensity of which are dependent on surface wave conditions such as wave age, wave slope, and wind-wave misalignment angle. At present, few modeling studies have explored the effects of wind-wave misalignment on wind stress and the mean wind profile, a feature difficult to observe in the open ocean and laboratory. We employ a large-eddy simulation for wind over a sinusoidal wave train to explore the characteristics of wave boundary turbulence modified by wind-wave misalignment under a range of strongly forced conditions. The LES methodology uses a wave-following coordinate system with a decomposition of wind velocity into wave mean, wave fluctuation, and turbulent fluctuation components. The mean and spatial structure of turbulence in such conditions is analyzed in the context of the drag coefficient and wave growth rate.