On the clouds of bubbles formed by breaking wind-waves in deep water, and their role in air-sea gas transfer

Thorpe, S. A.

doi:10.1098/rsta.1982.0011

Cited by 343 publications

(197 citation statements)

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“…Larger bubbles are more buoyant and rise toward the surface. Smaller bubbles, especially at greater depth, gradually dissolve [Thorpe, 1982]. Added to these effects, the turbulent boundary layer, which is maintained both by the relatively steady rip current and the harmonic forcing by the waves, enhances vertical diffusion within the water column and serves to offset vertical gradients in bubble concentration, which are an inevitable consequence of bubble buoyancy.…”

Section: Introductionmentioning

confidence: 99%

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Bubble transport in rip currents

Vagle¹,

Farmer²,

Deane³

2001

J. Geophys. Res.

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Abstract.A number of remote and in situ acoustical sensors were mounted in the surf zone off Scripps Pier, La Jolla, California, during March 1997 and used to characterize rip currents and their ability to transport bubbles offshore from the surf zone. The bubble size distributions and air fractions at the injection point were measured using an acoustical resonator and a conductivity sensor right in the surf zone. The offshore moving bubble plume was tracked with a multibeam 100 kHz Doppler sidescan sonar, giving the spatial extent and offshore variability in the rip events as well as information about the surface wave field. Furthermore, three acoustical resonators were mounted at 2.5 m depth 55-60 m farther offshore to probe the bubble field 300-400 s after injection. These results are interpreted using models that include bubble buoyancy and dissolution, rip current advection, and the turbulent boundary layer, which is represented by the Christoffersen and Jonsson [1985] formulation. IntroductionCoastlines are of great importance for recreation, commerce, and the military. However, man-made interference, sea level rise, and large storms threaten the sandy shorelines. Understanding the nearshore processes is therefore increasingly important. Sea and swell waves incident on a beach can drive strong quasi-steady currents in the surf zone. Gradients in wave radiation stress caused by breaking waves drive setup. The response of bubble clouds to advection and turbulence in the nearshore zone depends in a subtle way on buoyancy and gas dissolution. Indeed, a primary benefit of the interpretation of bubble measurements is that it leads to deeper insights on the flow dynamics and other aspects that may be only peripherally related to the bubbles themselves. Here we make use of acoustical techniques to measure the bubble field both in the surf zone and within rip currents and use the results to test our Bubble clouds generated in the surf zone move alongshore in the background flow. Intermittently, fluid is expelled seaward from the surf zone, carrying the bubbles with it. Smith and Largier [1995] used these bubbles as acoustic targets in studies of nearshore circulation. As the bubbles move seaward, the size distribution evolves. Larger bubbles are more buoyant and rise toward the surface. Smaller bubbles, especially at greater depth, gradually dissolve [Thorpe, 1982]. Added to these effects, the turbulent boundary layer, which is maintained both by the relatively steady rip current and the harmonic forcing by the waves, enhances vertical diffusion within the water column and serves to offset vertical gradients in bubble concentration, which are an inevitable consequence of bubble buoyancy. The bubble size distribution then becomes a 11,677

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Section: Introductionmentioning

confidence: 99%

“…Thorpe [1982] called these bubbles "dirty" to distinguish them from "clean" bubbles. Clean bubbles acquire a surface coating.…”

Section: Bubble Advection and Dissolutionmentioning

confidence: 99%

Bubble transport in rip currents

Vagle¹,

Farmer²,

Deane³

2001

J. Geophys. Res.

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“…Note that while we have compared W to the rise velocity in clean water, we have here to consider the rise velocity in dirty water. The rise velocity is then given by the formula from Thorpe (1982) and Woolf & Thorpe (1991) for a bubble rising in dirty water …”

Section: Normalized Bubble Size Distribution and Bubble Cloud Constantmentioning

confidence: 99%

“…From this decay rate, we can estimate an average bubble velocity by assuming that the path of the bubbles is given by the distance the bubble has to rise to reach the surface, which corresponds to the average penetration depth of the bubble cloud, say h. Thus we define the scale Figure 8b for three plunging breakers. The rise velocity of a bubble of radius r in clean water (for radius larger than 100µm) is given by Woolf & Thorpe (1991) (see also Thorpe (1982) for a review of bubble rise velocities),…”

Section: Decay Time and Rising Velocitiesmentioning

confidence: 99%

Air entrainment and bubble statistics in breaking waves

2016

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We investigate air entrainment and bubble statistics in three-dimensional breaking waves through novel direct numerical simulations of the two-phase air-water flow, resolving the length scales relevant for the bubble formation problem, the capillary length and the Hinze scale. The dissipation due to breaking is found to be in good agreement with previous experimental observations and inertial-scaling arguments. The air-entrainment properties and bubble-size statistics are investigated for various initial characteristic wave slopes. For radii larger than the Hinze scale, the bubble size distribution, can be described by N (r, t) = B(V 0 /2π)(ε(t − ∆τ )/W g)r −10/3 r −2/3 m during the active breaking stages, where ε(t − ∆τ ) is the time dependent turbulent dissipation rate, with ∆τ the collapse time of the initial air pocket entrained by the breaking wave, W a weighted vertical velocity of the bubble plume, r m the maximum bubble radius, g gravity, V 0 the initial volume of air entrained, r the bubble radius and B a dimensionless constant. The active breaking time-averaged bubble size distribution is described bȳ N (r) = B(1/2π)( l L c /W gρ)r −10/3 r −2/3 m , where l is the wave dissipation rate per unit length of breaking crest, ρ the water density and L c the length of breaking crest. Finally, the averaged total volume of entrained air,V , per breaking event can be simply related to l byV = B( l L c /W gρ), which leads to a relationship to a characteristic slope, S, of V ∝ S 5/2 . We propose a phenomenological turbulent bubble break-up model, based on earlier models and the balance between mechanical dissipation and work done against buoyancy forces. The model is consistent with the numerical results and existing experimental results.

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“…This model is still widely used despite the fact that air injection of bubbles is now recognized as a process that enhances the flux of oxygen into the sea [Kanwisher, 1963;Atkinson, 1973;Thorpe, 1982Thorpe, , 1984; Lamarre and Melville, 1991; Wallace and Wirick, 1992]. So, apart from being transported across the sea surface by molecular diffusion, oxygen is also transported by air bubbles injected into the water colunto as a result of wave breaking.…”

Section: Changes In Oxygen Contentmentioning

confidence: 99%

Net community production and oxygen fluxes in the Nordic Seas based on O₂ budget calculations

Falck¹,

Gade²

1999

Global Biogeochemical Cycles

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Abstract. Historical hydrographic data from 1955 to 1988 are applied to an oxygen model for the euphotic zone in an attempt to estimate the net community production in the Nordic Seas (Greenland, Iceland, and Norwegian Seas). The model requires prior knowledge of the net annual oxygen flux through the sea surface, which is achieved by an oxygen budget based on volume transports from the literature and observed oxygen concentrations. A net annual uptake of approximately 2.3 mol 02 m '2 is needed to balance the budget, indicating that the region acts as a sink for atmospheric oxygen. An oxygen budget for the euphotic zone is then compiled on the basis of observed monthly mean changes in oxygen content, which are assumed to be balanced by net air-sea oxygen exchange and net community production. Vertical exchange through the bottom of the euphotic zone and horizontal transports are ignored. The mean net community production in the Nordic Seas is found to be 36 g C m '2 y-i, but this result is sensitive to variations in the calculated oxygen fluxes which arise from the uncertainty of the parameterization of the airsea gas exchange.

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On the clouds of bubbles formed by breaking wind-waves in deep water, and their role in air-sea gas transfer

Cited by 343 publications

References 0 publications

Bubble transport in rip currents

Bubble transport in rip currents

Air entrainment and bubble statistics in breaking waves

Net community production and oxygen fluxes in the Nordic Seas based on O₂ budget calculations

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On the clouds of bubbles formed by breaking wind-waves in deep water, and their role in air-sea gas transfer

Cited by 343 publications

References 0 publications

Bubble transport in rip currents

Bubble transport in rip currents

Air entrainment and bubble statistics in breaking waves

Net community production and oxygen fluxes in the Nordic Seas based on O2 budget calculations

Contact Info

Product

Resources

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Net community production and oxygen fluxes in the Nordic Seas based on O₂ budget calculations