Modulation of Wind-Wave Breaking by Long Surface Waves

Vladimir A Dulov,Vladimir N Kudryavtsev,Vladimir V Malinovsky,Aleksandr E Korinenko

doi:10.3390/rs13142825

Abstract

This paper reports the results of field measurements of wave breaking modulations by dominant surface waves, taken from the Black Sea research platform at wind speeds ranging from 10 to 20 m/s. Wave breaking events were detected by video recordings of the sea surface synchronized and collocated with the wave gauge measurements. As observed, the main contribution to the fraction of the sea surface covered by whitecaps comes from the breaking of short gravity waves, with phase velocities exceeding 1.25 m/s. Averaging of the wave breaking over the same phases of the dominant long surface waves (LWs, with wavelengths in the range from 32 to 69 m) revealed strong modulation of whitecaps. Wave breaking occurs mainly on the crests of LWs and disappears in their troughs. Data analysis in terms of the modulation transfer function (MTF) shows that the magnitude of the MTF is about 20, it is weakly wind-dependent, and the maximum of whitecapping is windward-shifted from the LW-crest by 15 deg. A simple model of whitecaps modulations by the long waves is suggested. This model is in quantitative agreement with the measurements and correctly reproduces the modulations’ magnitude, phase, and non-sinusoidal shape.

Highlights

Wave breaking plays a crucial role in various air–sea interactions and remote sensing areas and has been the subject of intensive research over the past few decades
The whitecap coverage profiles were normalized with their mean values
Small variations of short-wave spectrum,the due to the of waves with the surface current of an arbitrary origin, result in a significantly amplified interaction of waves with the surface current of an arbitrary origin, result in a response of wave breaking to the non-uniform surface currents

Summary

Introduction

Wave breaking plays a crucial role in various air–sea interactions and remote sensing areas and has been the subject of intensive research over the past few decades (see, e.g., [1,2,3,4,5]). Wave breaking of wind-driven waves contributes substantially to air-sea gas exchange [6,7,8], wave energy and momentum dissipation [9,10,11], and generation of turbulence in the ocean near-surface layer [12,13,14]. Wind-wave modeling and forecasting need spectral parameterization for wave breaking [15,16]. Wave breaking affects radar backscattering [17,18,19,20] and microwave emission [21,22] of the sea. Wave breaking is very sensitive to the energy disturbances caused by wave interactions, with sub- and mesoscale surface current gradients being an important component of the wave energy balance. Various ocean phenomena, such as internal waves, eddies, current fronts, shallow water bathymetry are displayed on the ocean surface in the form of spatial anomalies of wave breaking parameters tracing the surface current features [23,24,25,26,27]

Results

Discussion

Conclusion