A Field Study of Whitecap Coverage and its Modulations by Energy Containing Surface Waves

Дулов, В. А.; Kudryavtsev, V. N.; Bol’shakov, A. N.

doi:10.1029/gm127p0187

Cited by 20 publications

(23 citation statements)

References 3 publications

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“…Of these, the two Reynolds numbers perform best. It has been shown previously that the primary contribution to wave breaking and resulting whitecaps comes from the high frequency components of the wave spectrum, and not the dominant waves [ Dulov et al ., ; Gemmrich et al ., ; Plant , ]. Therefore, the success of wind‐wave variables in accounting for variability in W may be improved with use of wave measurements describing the wind sea part of the spectrum only, e.g., the peak wave period for wind waves, rather than peak wave period of the total spectrum.…”

Section: Discussionmentioning

confidence: 99%

On the variability of whitecap fraction using satellite-based observations

Salisbury

Anguelova

Brooks

2013

J. Geophys. Res. Oceans

101

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[1] Despite decades of effort to accurately quantify whitecap fraction W using in situ photography of the ocean surface, there remains significant scatter in estimates for any given 10 m wind speed (U 10 ). It is believed that the resulting, commonly used, W(U 10 ) parameterizations do not fully account for the true variability in W, by failing to incorporate the impact of the wavefield and other environmental conditions. This paper attests to the variability in whitecap fraction attributed to these additional factors, by analyzing satellitederived W estimates over the globe for a full year. A comparison is made between the wind speed dependence of satellite estimates and three W(U 10 ) relationships formulated from in situ photographic data. The influence of various secondary factors on W is investigated once the dominant wind speed dependence is accounted for. The W retrieval's sensitivity to secondary forcings is dependent upon microwave frequency; at 37 GHz it varies by up to 25% of the mean at a given wind speed, while at 10 GHz it is a maximum of 8%. This results from a frequency-dependent sensitivity to foam depth; at 10 GHz predominantly foam from active breaking waves is detected, while at 37 GHz thin foam in residual whitecaps is also seen. Principal component analysis is used to rank variables by their success in accounting for variability in W. After wind speed, the most important secondary factor that accounts for variability in W is the wavefield. A wind-wave Reynolds number accounts for almost as much variability in W as wind speed.

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Section: Discussionmentioning

confidence: 99%

On the variability of whitecap fraction using satellite-based observations

Salisbury

Anguelova

Brooks

2013

J. Geophys. Res. Oceans

101

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“…However, there are also environmental factors implicated. For example, wavefield composition and development, wave‐current interaction and wind history all affect W. This is not surprising given that breaking rate and the scale of breaking waves change depending on the wavefield development and composition [ Dulov et al , 2002; Gemmrich et al , 2008], and both these parameters can be expected to impact W. Therefore the total instantaneous whitecap coverage is a function of breaking rate, breaking scale and foam decay processes.…”

Section: Discussionmentioning

confidence: 99%

Observed variation in the decay time of oceanic whitecap foam

Callaghan¹,

Deane²,

Stokes³

et al. 2012

J. Geophys. Res.

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[1] Whitecap foam decay times for 552 individual breaking waves determined from digital images of the sea surface are reported. The images had sub-centimeter pixel resolution and were acquired at frame rates between 3 and 6 frames per second at the Martha's Vineyard Coastal Observatory over a 10-day period in 2008, subdivided into 4 observation periods. Whitecap foam decay times for individual events varied between 0.2 s to 10.4 s across the entire data set. A systematic positive correlation between whitecap foam decay time and maximum whitecap foam patch area was found for each observation period. For a given whitecap size within each observation period, the decay times varied between a factor of 2 and 5, with the largest variation occurring during unsteady environmental forcing conditions. Within observation periods, bin-averaged decay times varied by up to a factor of 4 across the range of foam patch areas. Between observation periods, the effective whitecap foam decay time, which we define as the area-weighted mean decay time, varied by a factor of 3.4 between 1.4 s and 4.8 s. We found a weak correlation between decay times and individual event-averaged breaking wave speeds. The variation in the active breaking area across all 4 observation periods was small, indicating relatively uniform surface whitecap area generating potential. We speculate that the variation in the foam decay times may be due to (i) the effect of surfactants on bubble and foam stability, and (ii) differences between bubble plume characteristics caused by a variation in breaking wave type.

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“…Because of their amphiphilic nature, they preferentially reside at air-water boundaries such as the air-sea interface, and the surfaces of bubbles. Surfactants near the sea surface play important roles in the Earth's climate system by modulating the physics and chemistry of the upper ocean and sea surface microlayer (SML), increasing the drag force acting on a bubble as it rises through the water column, and prolonging the lifetime of foam cells at the water surface [e.g., Garrett, 1967bGarrett, ,1967cClift et al, 1978;J€ ahne et al, 1984;Ternes and Berg, 1984; Key Points: A surfactant effect in whitecap foam evolution is identifiable and largely confined to the decay stage A whitecap foam area stabilization factor (H) is defined to quantify this surfactant imprint Field and laboratory values of H show overlapping values…”

Section: Introductionmentioning

confidence: 99%

On the imprint of surfactant‐driven stabilization of laboratory breaking wave foam with comparison to oceanic whitecaps

2017

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Surfactants are ubiquitous in the global oceans: they help form the materially‐distinct sea surface microlayer (SML) across which global ocean‐atmosphere exchanges take place, and they reside on the surfaces of bubbles and whitecap foam cells prolonging their lifetime thus altering ocean albedo. Despite their importance, the occurrence, spatial distribution, and composition of surfactants within the upper ocean and the SML remains under‐characterized during conditions of vigorous wave breaking when in‐situ sampling methods are difficult to implement. Additionally, no quantitative framework exists to evaluate the importance of surfactant activity on ocean whitecap foam coverage estimates. Here we use individual laboratory breaking waves generated in filtered seawater and seawater with added soluble surfactant to identify the imprint of surfactant activity in whitecap foam evolution. The data show a distinct surfactant imprint in the decay phase of foam evolution. The area‐time‐integral of foam evolution is used to develop a time‐varying stabilization function, ϕ(t) and a stabilization factor, normalΘ, which can be used to identify and quantify the extent of this surfactant imprint for individual breaking waves. The approach is then applied to wind‐driven oceanic whitecaps, and the laboratory and ocean normalΘ distributions overlap. It is proposed that whitecap foam evolution may be used to determine the occurrence and extent of oceanic surfactant activity to complement traditional in‐situ techniques and extend measurement capabilities to more severe sea states occurring at wind speeds in excess of about 10 m/s. The analysis procedure also provides a framework to assess surfactant‐driven variability within and between whitecap coverage data sets.

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A Field Study of Whitecap Coverage and its Modulations by Energy Containing Surface Waves

Cited by 20 publications

References 3 publications

On the variability of whitecap fraction using satellite-based observations

On the variability of whitecap fraction using satellite-based observations

Observed variation in the decay time of oceanic whitecap foam

On the imprint of surfactant‐driven stabilization of laboratory breaking wave foam with comparison to oceanic whitecaps

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