The equilibrium dynamics and statistics of gravity-capillary waves

TitleThe equilibrium dynamics and statistics of gravity-capillary waves
Publication TypeJournal Article
Year of Publication2015
AuthorsMelville W.K, Fedorov A.V
JournalJournal of Fluid Mechanics
Volume767
Pagination449-466
Date Published2015/03
Type of ArticleArticle
ISBN Number0022-1120
Accession NumberWOS:000349688900023
Keywordsbreaking waves; capillaries; capillary waves; energy-dissipation; field; generation; parasitic; steep water-waves; surface gravity waves; surface-tension; wind; wind wave interactions
Abstract

Recent field observations and modelling of breaking surface gravity waves suggest that air-entraining breaking is not sufficiently dissipative of surface gravity waves to balance the dynamics of wind-wave growth and nonlinear interactions with dissipation for the shorter gravity W'aves of O(10) cm wavelength. 'fheories of parasitic capillary waves that form at the crest and forward face of shorter steep gravity waves have shown that the dissipative effects of these waves may be one to two orders of magnitude greater than the viscous dissipation of the underlying gravity Waves. Thus the parasitic capillaries may provide the required dissipation of the short wind -generated gravity Waves. This has been the subject of speculation and conjecture in the literature, Using the nonlinear theory of Fedorov cV. Melville Fluid Mech., vol. 354, 1998, pp. 1-42), we show that the dissipation due to the parasitic capillaries is sufficient to balance the wind input to the short gravity waves over some range of wave ages and wave slopes. 'The range of gravity wave lengths on which these parasitic capillary waves are dynamically significant approximately corresponds to the range of short gravity waves that Cox & Munk (j. Mar Res., vol. 13, 1954, pp. 198-227) found contributed significantly to the mean square slope of the ocean surface, which they measured to be proportional to the wind speed. Here we show that the mean square slope predicted by the theory is proportional to the square of the friction velocity of the wind, IC, for small wave slopes, and approximately 14, for larger slopes.

DOI10.1017/jfm.2014.740
Short TitleJ. Fluid Mech.
Student Publication: 
No