Relative current effect on short wave growth

Guimar„es, Pedro Veras ; Ardhuin, Fabrice ; Perignon, Yves ; Benetazzo, Alvise ; Bouin, Marie-NoŽlle ; Garnier, Valerie ; Redelsperger, Jean-Luc ; Accensi, Mickael ; Thomson, Jim

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<p align=justify>Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and breaking, modifying the surface roughness, and consequently their growth. However, this interplay is poorly understood and observations are scarce. This work uses in situ measurements of near-surface winds, surface current, and waves under strong tidal current conditions to investigate the relative wind speed effect on the local short waves growth. Those observations were extensive compared with numerical modeling using WAVEWACHIII, where the simulations repeatedly fail to reproduce the observed wind sea energy under strong current conditions. Our field observations and coupled ocean-atmosphere numerical simulations suggest that surface currents can strongly modulate surface winds. That is a local process, better observed closer to the boundary layer than at 10 m height. Yet, it can cause a significant impact on the local wind shear estimation and consequently on the local waves' growth source term. The results presented here show that the relative wind effect is not well solved inside spectral waves models, causing a significant bias around the peak of wind sea energy.</p>
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