A Whitecap Coverage Model Based on the Surface Slope For Criterion of Wave Breaking

Using the limit surface slope as a criterion of wave breaking, a simple model for estimating the spatial fraction of breaking surface of sea at an instant, which is regarded as the whitecap coverge in this paper, is analytically derived from the probability density of surface slope based on Gaussian statistics. The resulting fraction is found depending on the fourth moment of wave spectum, m(4), as well as the critical threshold of surface slope. By expressing the fourth moment in terms of the Neumann spectrum, a formula linking the fraction and wind speed for fully developed sea states is obtianed. Another formula relating the fraction to both wind speed and fetch (or duration) is achieved by expressing m, in terms of the Krylov spectrum and applying the empirical relationships used in the SMB ocean wave predicting technique. A comparison between these results and the field data of whitecap coverage collected by Monahan and O'Muircheartuigh shows an encouraging agreement.

海洋白浪覆盖率模式的研究

在波面位移为均匀正态分布的假定下，导出了以海浪谱矩为参量的波面斜率分布函数。依此函数，利用极限波面斜率为波浪破碎判据导出依赖于海浪港四阶矩的白浪覆盖率的表示式。又通过Krylov谱和SMB海浪预报方法的经验公式，将海浪谱四阶矩代之以风要素，从而首次建立了一个依赖于风速和风区两者的半理论、半经验的海洋白浪覆盖率模式。此模式给出的结果与Monahan汇集的海洋白浪覆盖率测量数据符合颇佳。

海洋环境因素对白冠覆盖率的影响及其数值估算

波浪破碎是一个强非线性过程,破碎时产生的大量气泡在海面上表现为白冠,白冠覆盖率是刻画波浪破碎一个重要参数。研究表明,白冠覆盖率与海上风速、海浪状态和大气稳定度等多种海洋环境因素有关。综合前人的观测数据,本文给出了更为可靠的依赖风速的白冠覆盖率公式,发现海水温度越高,白冠覆盖率越大。提出了以波浪破碎耗散函数为参数的白冠覆盖率公式,同时发现波龄小于某个临界值时,白冠覆盖率随波龄增大,波龄大于临界值时,白冠覆盖率保持不变,该临界值随风速增大而减小。