On the effect of wind and turbulence on ocean swell

A quantitave review of processes contributing to the evolution of swell is proposed, combining direct interactions of swell with the wind and upper ocean turbulence, and interaction with shorter wind waves. The interaction with short waves is based on the extension of Hasselmann's (197 1) theory for short wave modulation by long wave to the presence of variable wind stresses. Quantitative estimations of the various effects are performed based on the wave modulation model of Hara et al. (2003) and the wind-over-wave coupling model of Kudryavtsev and Makin (2004). It is found that the observations of swell decay in the Pacific (Snodgrass et al., 1963) are quantitatively consistent with the effects of wind stress modulation and direct wind to wave momentum transfer.