Turbulence from Breaking Surface Waves at a River Mouth

Zippel, Seth; Thomson, Jim; Farquharson, Gordon

doi:10.1175/jpo-d-17-0122.1

Cited by 23 publications

(21 citation statements)

References 64 publications

(112 reference statements)

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“…Using τ p = w p /g, we find τ p ≈ 0.001 s. Wind wave periods are on the order of seconds, so St w = O(10 −3 ) ≪ 1 and the assumption of no particle inertia is valid. In terms of the turbulence, a conservative estimate using a high dissipation rate at the ocean surface boundary layer of 10 −3 m 2 /s 3 corresponds to τ η ≈ 0.03 s (Zippel et al, 2018). In this case, St η = O(10 −2 ) ≪ 1 as well.…”

Section: Methodsmentioning

confidence: 98%

Non-breaking Wave Effects on Buoyant Particle Distributions

DiBenedetto

2020

Front. Mar. Sci.

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The dispersal of buoyant particles in the ocean mixed layer is influenced by a variety of physical factors including wind, waves, and turbulence. Microplastics observations are often made at the free surface, which is strongly forced by surface gravity waves. Many studies have used numerical simulations to examine how turbulence and wave effects (e.g., breaking waves, Langmuir circulation) control buoyant particle dispersal at the ocean surface. However these simulations are not wave phase-resolving. Therefore, the effects of an unsteady free surface due to surface gravity waves remain unknown in this context. To address this, we develop an analytical model for the distribution of buoyant particles as a function of wave-phase under wind-wave conditions in deep-water. Using this analytical model and complementary numerical simulations, we quantify the effects of a nonbreaking, monochromatic, progressive wave train on the equilibrium vertical and horizontal distributions of buoyant particles. We find that waves result in non-uniform horizontal distributions of particles with more particles under the wave crests than the troughs. We also find that the waves can stretch or compress the equilibrium vertical distribution. Finally, we consider the effects of waves on the sampling of microplastics with a towed net, and we show that waves have the ability to lower the measured concentrations relative to nets sampling without the influence of waves.

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Section: Methodsmentioning

confidence: 98%

Non-breaking Wave Effects on Buoyant Particle Distributions

DiBenedetto

2020

Front. Mar. Sci.

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“…Turbulent dissipation profiles ϵ ( z ) are estimated by fitting the structure function to a r 2/3 dependence following the methods in Thomson () and Zippel and Thomson (). This method has been validated by comparison with ADV point measurements of dissipation (Thomson, ) and dissipation profiles estimated using frequency spectra (Zippel et al, ). The application of the structure function here varies from previous applications primarily in that it uses only measurements within six bins of each depth (6 r ) and is double‐sided.…”

Section: Methodsmentioning

confidence: 99%

Ocean Surface Turbulence in Newly Formed Marginal Ice Zones

Smith

Thomson

2019

JGR Oceans

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Near‐surface turbulent kinetic energy dissipation rates are altered by the presence of sea ice in the marginal ice zone, with significant implications for exchanges at the air‐ice‐ocean interface. Observations spanning a range of conditions are used to parameterize dissipation rates in marginal ice zones with relatively thin, newly formed ice, and two regimes are identified. In both regimes, the turbulent dissipation rates are matched to the turbulent input rate, which is formulated as the surface stress acting on roughness elements moving at an effective transfer velocity. In marginal ice zones with waves, the short waves are the roughness elements, and the phase speed of these waves is the effective transfer velocity. The wave amplitudes are attenuated by the ice, and thus, the size of the roughness elements is reduced; this is parameterized as a reduction in the effective transfer velocity. When waves are sufficiently small, the ice floes are the roughness elements, and the relative velocity between the sea ice and the ocean is the effective transfer velocity. A scaling is introduced to determine the appropriate transfer velocity in a marginal ice zone based on wave height, ice thickness and concentration, and ice‐ocean shear. The results suggest that turbulence underneath new sea ice is mostly related to the wind forcing and that marginal ice zones generally have less turbulence than the open ocean under similar wind forcing.

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“…Some of this work is based on observations of bubble clouds (Thorpe, ; Wang et al, ). It is nevertheless clear that the law‐of‐the‐wall scaling does not hold in the breaking zone (Fisher et al, ; Gemmrich, ; Sutherland & Melville, ; Thomson et al, ; Zippel et al, ). Vertical size‐specific bubble distributions for radii between 8 and 130

normalμ

m were measured by Vagle and Farmer () using a multifrequency acoustic backscatter technique.…”

Section: Introductionmentioning

confidence: 99%

Long‐Term Statistics of Observed Bubble Depth Versus Modeled Wave Dissipation

et al. 2020

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Air bubble penetration depths are investigated with a bottom‐mounted echosounder at a seabed observatory in northern Norway. We compare a 1‐year time series of observed bubble depth against modeled and estimated turbulent kinetic energy flux from breaking waves as well as wind speed and sea state. We find that the hourly mean and maximum bubble depths are highly variable, reaching 18 and 38 m, respectively, and strongly correlated with wind and sea state. The bubble depth is shallowest during summer following the seasonal variations in wind speed and wave height. Summertime shallowing of the mixed layer depth is not limiting the penetration depth. A strong relationship between bubble depth and modeled turbulent kinetic energy flux from breaking waves is found, similar in strength to the relationship between bubble depth and wind speed. The wind sea is more strongly correlated with bubble depth than the total significant wave height, and the swell is only weakly correlated, suggesting that the wave model does a reasonable separation of swell and wind sea.

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Turbulence from Breaking Surface Waves at a River Mouth

Cited by 23 publications

References 64 publications

Non-breaking Wave Effects on Buoyant Particle Distributions

Non-breaking Wave Effects on Buoyant Particle Distributions

Ocean Surface Turbulence in Newly Formed Marginal Ice Zones

Long‐Term Statistics of Observed Bubble Depth Versus Modeled Wave Dissipation

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