A WHITECAP COVERAGE MODEL-BASED ON THE SURFACE SLOPE FOR CRITERION OFWAVE BREAKING

Using the limit surface slope as a criterion of wave breaking, a simpl e model for estimating the spatial fraction of breaking surface of sea at an instant, which is regarded as the whitecap coverge in this pape r, is analytically derived from the probability density of surface slo pe based on Gaussian statistics. The resulting fraction is found depen ding on the fourth moment of wave spectum, m(4), as well as the critic al threshold of surface slope. By expressing the fourth moment in term s of the Neumann spectrum, a formula linking the fraction and wind spe ed for fully developed sea states is obtianed. Another formula relatin g the fraction to both wind speed and fetch (or duration) is achieved by expressing m, in terms of the Krylov spectrum and applying the empi rical relationships used in the SMB ocean wave predicting technique. A comparison between these results and the field data of whitecap cover age collected by Monahan and O'Muircheartuigh shows an encouraging agr eement.