Statistical characteristics of wave breakings and their relation with the wind waves’ energy dissipation based on the field measurements

Abstract

Purpose. The work is aimed at studying geometric similarity of wind wave breakings in natural conditions, estimating the Duncan constant which connects the wave energy dissipation conditioned by wave breakings, with distribution of the lengths of a breaking wave fronts Λ(с). Methods and Results. The field measurements of the wave breaking characteristics were carried out at the stationary oceanographic platform located in the Golubaya Bay near the Katsiveli village. Geometric dimensions of the wave breakings’ active phase, velocities and directions of their movement were determined from the video records of the sea surface; simultaneously, the meteorological information was recorded and the surface waves’ characteristics were measured. Altogether 55 video recordings (duration 40–50 mins) of the sea surface were obtained. The measurements were carried out in a wide range of meteorological conditions and wave parameters (wind speed varied from 9.2 to 21.4 m/s). Conclusions. It is found that the probability densities of the ratio between the maximum length of a breaking and the length of a breaking wave, obtained in various wind and wave conditions are similar. The average value of this ratio is 0.1. Distributions of the wave breakings’ total length are constructed in the movement velocity intervals on a surface unit. It is shown that the experimental estimates of dependence of these distributions upon the wind speed and the wave breaking movement velocity are consistent with the theoretical predictions of O.M. Phillips (1985); at that no dependence on the waves’ age was found. Quantitative characteristics of the relation between the wave lengths’ distribution and the energy dissipation are obtained. The Duncan constant was estimated; it turned out to be equal to 1.8⋅10-3 and independent upon the waves’ and atmosphere parameters.