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- Title
On the Groupiness and Intermittency of Oceanic Whitecaps.
- Authors
Malila, M. P.; Thomson, J.; Breivik, Ø.; Benetazzo, A.; Scanlon, B.; Ward, B.
- Abstract
The enhancement of wave breaking activity during wave group passage is investigated using coherent field observations of the instantaneous sea surface elevation and whitecap coverage from platform‐based stereo video measurements in the central North Sea. Passing wave groups are shown to be associated with a two to threefold enhancement in the probability distribution of total whitecap coverage W whereas the enhancement of active whitecap coverage WA is approximately fivefold. Breaking time scales and intermittency characteristics are also investigated with the inclusion of a secondary data set of W and WA observations collected during a research cruise in the North Pacific. The time scale analysis suggests a universal periodicity in wave breaking activity within a representative sea‐surface area encompassing approximately one dominant wave crest. The breaking periodicity is shown to be closely linked to the peak period of the dominant wave components, suggesting that long‐wave modulation of wave breaking is a predominant mechanism controlling the intermittency of wave breaking across scales. Plain Language Summary: In the open ocean, wind waves of similar wavelength, period and direction combine to form wave groups, also known as sets to surfers and other beachgoers. In deep water, the individual waves in groups travel twice as fast as the groups themselves, and momentarily grow in height and steepness in the wave group center, making them theoretically more likely to break. We show, using field observations of wave breaking taken with digital video cameras, that waves in deep water are up to five times more likely to break in large wave groups than during lulls in the wave field. We also show that the large, dominant wave groups regularly initiate wave breaking at a wide range of scales. Our findings can be used to produce more accurate predictions of when individual waves will break, an active and relatively poorly understood area of current wave research. Key Points: Wave breaking activity and extent is significantly enhanced in wave groupsThe periodicity of the oceanic whitecap coverage is closely linked to the periodicity of dominant wave componentsThe intermittency characteristics of whitecap coverage approximately follow similarity scaling laws of other general stochastic processes
- Subjects
NORTH Sea; INTERMITTENCY (Nuclear physics); OCEAN waves; STOCHASTIC processes; MODULATION theory
- Publication
Journal of Geophysical Research. Oceans, 2022, Vol 127, Issue 1, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2021JC017938