| This thesis consists of two parts. The first part is a statistical study about the probability of wave breaking and the fraction of sea surface covered by breaking water (ie. whitecap coverage), while the second part is a dynamical study about the influence of nonuniform current fields on the breaking of short wind waves. Part I: Since the study about breaking onset criteria base on the downward acceleration or on the wave slope shows great discrepancy, the models that estimating breaking probability and whitecap coverage according to these two . criteria are problematic. And what makes it even worse, these models also depend on the forth-order spectral momentum of wind wave spectrum, which is infinite for those normally used wind wave spectrums. On the other hand, various study in recent years about the kinematical breaking criterion show consistently that this breaking criterion persists under different conditions. Therefore, in this thesis, a new set of models about breaking probability and whitecap coverage is set up using this breaking criterion.Under the assumption of linear ocean waves, and in the light of the theoretical framework about the probabilistic distribution of wave characteristics( Sun Fu 1988), several probabilistic distributions of wave characteristics that is necessary for the estimation of breaking probability and whitecap coverage are derived. Afterwards, the models of breaking probability and whitecap coverage are set up with these distributions in addition to the kinematical criterion.In order to develop these analytical models into practically applicable forms, the forth order momentum of JONS WAP spectrum is estimated using the time-averaging technique (Glazman 1986). However, we found that the formulae he given for the estimation of even-order momentum are inconsistent with that for odd-order ones. Hence a new set of formulae for odd-order momentum estimation is strictly derived out. After that the practically applicable forms of the analytical models are developed through fitting the analytical model with field data. The fitting between them are acceptable. In addition, the effect of surface drift on wind wave breaking , as well as some statistical characteristics of three-dimensional waves are also discussed. Part II: A third possible mechanism for the effect of nonuniform current on short waves is suggested, which ascribes the modulation of short wave spectrum by current to that the current changes the drift, through which it changes the breaking criteria, as a result the energy dissipation is altered.When a strong tide is disturbed by submarine bedforms, its effect on surface drift, breaking criteria, as well as energy dissipation rate of short wind waves are discussed and for a particular case, these effects are estimated using available experimental formulae for drift speed. The calculation shows that these effects are significant for waves at wavelength not much longer than 1m, especially when the water are not very deep, and the direction of the current is the reverse of that of the wind. Therefore this kind of mechanism shall be taken seriously in ocean remote sensing.
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