The Saturation of Fluid Turbulence in Breaking Laboratory Waves and Implications for Whitecaps

Deane, Grant B.; Stokes, M. Dale; Callaghan, Adrian H.

doi:10.1175/jpo-d-14-0187.1

Cited by 27 publications

(41 citation statements)

References 50 publications

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“…Their experimental data showed a linear relationship between total breaking wave energy dissipation measured in Joules, and the evolving two‐phase flow volume integrated in time during the whitecap area growth phase. These findings are consistent with the idea that turbulence within breaking waves that exceed a minimum scale saturates and total energy dissipated by the air entraining, two‐phase flow, is proportional to flow volume [ Deane et al ., ].…”

Section: Relevance To the Remote Sensing Of Breaking Wave Energy Dissmentioning

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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Section: Relevance To the Remote Sensing Of Breaking Wave Energy Dissmentioning

confidence: 99%

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

2017

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“…Previous laboratory measurements have shown that the maximum volume of air entrained by breaking waves scales with energy dissipation [ Lamarre and Melville , ]. Recently, the saturation of fluid turbulence within breaking wave crests has been reported using direct and indirect measurement techniques [ Deane et al, ]. These observations show that the space and time averaged dissipation rate of turbulent kinetic energy, ε , inside actively breaking wave crests is largely independent of breaking wave scale: larger, more energetic breaking waves lead to an increase in air entrainment, but without significant increases in averaged turbulent intensity.…”

Section: Introductionmentioning

confidence: 99%

Laboratory air‐entraining breaking waves: Imaging visible foam signatures to estimate energy dissipation

Callaghan

Deane

Stokes

2016

Geophysical Research Letters

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Oceanic air‐entraining breaking waves fundamentally influence weather and climate through bubble‐mediated ocean‐atmosphere exchanges, and influence marine engineering design by impacting statistics of wave heights, crest heights, and wave loading. However, estimating individual breaking wave energy dissipation in the field remains a fundamental problem. Using laboratory experiments, we introduce a new method to estimate energy dissipation by individual breaking waves using above‐water images of evolving foam. The data show the volume of the breaking wave two‐phase flow integrated in time during active breaking scales linearly with wave energy dissipated. To determine the volume time‐integral, above‐water images of surface foam provide the breaking wave timescale and horizontal extent of the submerged bubble plume, and the foam decay time provides an estimate of the bubble plume penetration depth. We anticipate that this novel remote sensing method will improve predictions of air‐sea exchanges, validate models of wave energy dissipation, and inform ocean engineering design.

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“…A further factor that may affect the parameterization of K using ε is that recent laboratory measurements by Deane et al (2016) find that turbulence dissipation near the breaking wave crest is saturated and does not vary much with wavelength and slope. They suggest that either bubbles limit the degree of turbulence intensity or the turbulence is spread across varying depths.…”

Section: Turbulent Energy Dissipation Ratementioning

confidence: 99%

Gradient flux measurements of sea–air DMS transfer during the Surface Ocean Aerosol Production (SOAP) experiment

et al. 2018

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Abstract. Direct measurements of marine dimethylsulfide (DMS) fluxes are sparse, particularly in the Southern Ocean. The Surface Ocean Aerosol Production (SOAP) voyage in February-March 2012 examined the distribution and flux of DMS in a biologically active frontal system in the southwest Pacific Ocean. Three distinct phytoplankton blooms were studied with oceanic DMS concentrations as high as 25 nmol L −1 . Measurements of DMS fluxes were made using two independent methods: the eddy covariance (EC) technique using atmospheric pressure chemical ionization-mass spectrometry (API-CIMS) and the gradient flux (GF) technique from an autonomous catamaran platform. Catamaran flux measurements are relatively unaffected by airflow distortion and are made close to the water surface, where gas gradients are largest. Flux measurements were complemented by near-surface hydrographic measurements to elucidate physical factors influencing DMS emission. Individual DMS fluxes derived by EC showed significant scatter and, at times, consistent departures from the Coupled Ocean-Atmosphere Response Experiment gas transfer algorithm (COAREG). A direct comparison between the two flux methods was carried out to separate instrumental effects from environmental effects and showed good agreement with a regression slope of 0.96 (r 2 = 0.89). A period of abnormal downward atmospheric heat flux enhanced near-surface ocean stratification and reduced turbulent exchange, during which GF and EC transfer velocities showed good agreement but modelled COAREG values were significantly higher. The transfer velocity derived from near-surface ocean turbulence measurements on a spar buoy compared well with the COAREG model in general but showed less variation. This first direct comparison between EC and GF fluxes of DMS provides confidence in compilation of flux estimates from both techniques, as well as in the stable periods when the observations are not well predicted by the COAREG model.

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The Saturation of Fluid Turbulence in Breaking Laboratory Waves and Implications for Whitecaps

Cited by 27 publications

References 50 publications

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

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

Laboratory air‐entraining breaking waves: Imaging visible foam signatures to estimate energy dissipation

Gradient flux measurements of sea–air DMS transfer during the Surface Ocean Aerosol Production (SOAP) experiment

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