Field Observations of Breaking of Dominant Surface Waves

Pavel Pivaev,Aleksandr Korinenko,Vladimir Kudryavtsev,Vladimir Malinovsky

doi:10.3390/rs13163321

Pavel Pivaev, Aleksandr Korinenko + Show 2 more

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https://doi.org/10.3390/rs13163321

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Abstract

The results of field observations of breaking of surface spectral peak waves, taken from an oceanographic research platform, are presented. Whitecaps generated by breaking surface waves were detected using video recordings of the sea surface, accompanied by co-located measurements of waves and wind velocity. Whitecaps were separated according to the speed of their movement, c, and then described in terms of spectral distributions of their areas and lengths over c. The contribution of dominant waves to the whitecap coverage varies with the wave age and attains more than 50% when seas are young. As found, the whitecap coverage and the total length of whitecaps generated by dominant waves exhibit strong dependence on the dominant wave steepness, ϵp, the former being proportional to ϵp6. This result supports a parameterization of the dissipation term, used in the WAM model. A semi-empirical model of the whitecap coverage, where contributions of breaking of dominant and equilibrium range waves are separated, is suggested.

Highlights

The breaking of ocean surface waves has been a subject of extensive scientific investigations over the past decades, and significant progress in understanding of underlying physics and statistical properties of breaking waves has already been made [1,2,3,4]
The aim of the present study is to investigate whitecaps generated by breaking of spectral peak waves and relationships between properties of the whitecaps and wind speed, as well as properties of dominant waves, using video imagery of the sea surface in the visible range
Similar to the definition of Λ(c), we introduce an active whitecap coverage distribution, q(c), such that q(c)dc represents the fraction of the sea surface covered by whitecaps that move with speeds in range (c, c + dc)

Summary

Introduction

The breaking of ocean surface waves has been a subject of extensive scientific investigations over the past decades, and significant progress in understanding of underlying physics and statistical properties of breaking waves has already been made [1,2,3,4]. Radar returns from breaking waves can apparently result in overestimation of the sea surface height derived from space-born altimeters [16], thereby forming a part of a so-called sea state bias in altimeter data [17,18,19]. Dielectric properties of foam produced by breaking waves differ from those of water and notably affect surface microwave emissivity, which is necessary to take into account in processing and interpretation of the measurements made by space-born passive microwave instruments [20,21,22]. Availability and extensive use of satellite microwave data in L-band had led to comprehension that breaking of large-scale waves produces the thickest foam that can significantly impact measurements of passive microwave instruments in this frequency band [23,24]

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