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Titolo:
MULTIFRACTAL REPRESENTATION OF BREAKING WAVES ON THE OCEAN SURFACE
Autore:
KERMAN BR; BERNIER L;
Indirizzi:
ENVIRONM CANADA,CANADA CTR INLAND WATERS,ATMOSPHER ENVIRONM SERV BURLINGTON L7R 4A6 ONTARIO CANADA MCGILL UNIV,DEPT COMP SCI MONTREAL H3A 2A7 QUEBEC CANADA
Titolo Testata:
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
fascicolo: C8, volume: 99, anno: 1994,
pagine: 16179 - 16196
SICI:
2169-9275(1994)99:C8<16179:MROBWO>2.0.ZU;2-M
Fonte:
ISI
Lingua:
ENG
Soggetto:
THRESHOLD MECHANISM; WIND-SPEED; WHITECAPS; TURBULENCE; FIELD; SEA; CLOUDS; WATER;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
39
Recensione:
Indirizzi per estratti:
Citazione:
B.R. Kerman e L. Bernier, "MULTIFRACTAL REPRESENTATION OF BREAKING WAVES ON THE OCEAN SURFACE", J GEO RES-O, 99(C8), 1994, pp. 16179-16196

Abstract

It is established for the first time that the spatial distribution ofbreaking waves on the ocean surface is a multifractal process. This result is based on an analysis of airborne visible and near-infrared imagery of the ocean surface under a limited range of wind speed and fetch. A detailed study of the optical spectra of the images and the cumulative probability structure of the prevalent background shows that the lower-intensity reflective areas follow a Rayleigh probability distribution. By contrast, the higher-intensity pixels associated with the scattered light from foam and breaking waves demonstrate scaling characteristics in both the optical spectra and the cumulative probability distributions. It is demonstrated that the degree to which the whitecaps are singularities on a dark background is described by a Lipschitz exponent alpha, which uniquely tags each breaking wave. This identification process, called ''fractal'' or ''singularity filtering'', leads to a critical condition alpha(c) = 1 tentatively associated with the crossover from active entraining whitecaps to passively dissipating foam. The multifractal representation associated with the degree of singularity is simply a restatement that the imagery is composed of a continuum of sets, where each set consists of those breaking waves at a particular phase in their existence. The fractal spectrum of the image above a threshold is shown to be representable by a fractal generator. Physically, the fractal generator models the energy exchange in a breaking wave field as a flux of energy input from the atmosphere to the wave field cascaded over scales of the order of a kilometer to meters. If the energy flux is further parameterized in terms of the receiving area, an assumption similar to closure techniques used in classical turbulence models, the empirical results symmetrically span Phillips's basic arguments for the energy flux terms controlling a wind-driven sea.

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Documento generato il 28/11/20 alle ore 09:45:48