Fine structure of laboratory wind-wave surfaces studied using an optical method

The fine structure of laboratory wind-wave surfaces was investigated using an optical method. Several characteristic structures, closely associated with wind speed and the stage of development of the waves, are described. A parallel light, incident on the wind-wave surface, was backscattered by ‘specular facets’ perpendicular to the incident angle. These specular facets, which represented the fine structures, were photographed and quantitatively analyzed by image processing techniques.For wind speeds ranging from 3.6 to 13.6 m s−1, different types of small-scale undulations appeared: a three-dimensional rhombic structure; a train of capillary waves on the forward face with wavelengths gradually decreasing with distance from the crest, and a streaky structure on the backward face in the direction of the wind; and random and wide-spreading irregularities covering the whole wind-wave surface. The spatial scales and temporal variation of the undulations are described.

[1]  Jin Wu.  Slope and Curvature Distributions of Wind-Disturbed Water Surface , 1971 .

[2]  Yoshiaki Toba,et al.  A Parameter Describing Overall Conditions of Wave Breaking, Whitecapping, Sea-Spray Production and Wind Stress , 1986 .

[3]  G. Csanady.  Air-Sea Momentum Transfer by Means of Short-Crested Wavelets , 1985 .

[4]  John W. McLean,et al.  Instabilities of finite-amplitude water waves , 1982, Journal of Fluid Mechanics.

[5]  C. Cox.  Statistics of the sea surface derived from sun glitter , 1954 .

[6]  M. Longuet-Higgins,et al.  The generation of capillary waves by steep gravity waves , 1963, Journal of Fluid Mechanics.

[7]  H. Kawamura,et al.  Ordered motion in the turbulent boundary layer over wind waves , 1988, Journal of Fluid Mechanics.

[8]  Gaspar R. Valenzuela,et al.  Microwave Sensing of the Ocean Surface , 1985 .

[9]  K. Okuda.  Internal flow structure of short wind waves , 1984 .

[10]  Brian J. Cantwell,et al.  Organized Motion in Turbulent Flow , 1981 .

[11]  Richard N. Wagner,et al.  Measurement of high frequency capillary waves on steep gravity waves , 1978, Journal of Fluid Mechanics.

[12]  F. A. Schraub,et al.  The structure of turbulent boundary layers , 1967, Journal of Fluid Mechanics.

[13]  K. Okuda.  Internal flow structure of short wind waves , 1982 .

[14]  J. Wright,et al.  Backscattering from capillary waves with application to sea clutter , 1966 .

[15]  O. Shemdin,et al.  An investigation of the modulation of capillary and short gravity waves in the open ocean , 1980 .

[16]  D. Crombie,et al.  Doppler Spectrum of Sea Echo at 13.56 Mc./s. , 1955, Nature.

[17]  Daniel S. Kwoh,et al.  The Nature of Microwave Backscattering from Water Waves , 1985 .

[18]  H. Mitsuyasu,et al.  The high frequency spectrum of wind-generated waves , 1974 .

[19]  E. H. Fooks,et al.  On the microwave reflectivity of small-scale breaking water waves , 1985, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[20]  S. Kawai.  Structure of air flow separation over wind wave crests , 1982 .

[21]  Ron F. Blackwelder,et al.  Streamwise vortices associated with the bursting phenomenon , 1979, Journal of Fluid Mechanics.

[22]  Hsien-Ta Liu,et al.  On the spectra of high-frequency wind waves , 1982, Journal of Fluid Mechanics.

[23]  Allen H. Schooley,et al.  A Simple Optical Method for Measuring the Statistical Distribution of Water Surface Slopes , 1954 .

[24]  Y. Toba,et al.  Statistical characteristics of individual waves in laboratory wind waves , 1982 .

[25]  S. Kawai.  Generation of initial wavelets by instability of a coupled shear flow and their evolution to wind waves , 1979, Journal of Fluid Mechanics.

[26]  Momoki Koga,et al.  Bubble entrainment in breaking wind waves , 1982 .