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Vertical profiles of the wave-coherent airflow over ocean waves

Amplitude and phase of the wave-induced components of the wind relative to the waves for various wind-wave conditions at each height were computed spectrally. Results show that the wave-induced fluctuations depend on both the critical height *z _{c}* and the normalized height

*kz*. The critical height

*z*is defined as the height where the mean wind speed

_{c}*U(z*equals the phase speed of the waves

_{c})*c*. The normalized height

*kz*is the height of the anemometers

*z*normalized by the wavenumber

*k*of the waves with

*k = g/c*.

^{2}In the neighborhood of the critical height, results are qualitatively consistent with the critical layer theory of Miles (1957). Across the critical height, the wave-induced vertical and horizontal velocities change significantly in both amplitude and phase. Below the critical layers, a suitable normalization of the wave-induced fluctuations collapses the data from all the anemometers, on a curve which follows an exponential decay with the normalized height *kz*.

References:

Miles J. W. (1957). On the generation of surface waves by shear flows. *J. Fluid. Mech.*, Vol 3, 185-204.

Sullivan et al. (2014). Large eddy simulation of marine atmospheric boundary layers above a spectrum of moving waves. *J. Atmos. Sci.*, Advance online publication. doi: 10.1175/JAS-D-14-0095.1