Density Stratification, Turbulence, but How Much Mixing?

Ivey, Gregory; Winters, K.B.; Koseff, Jeffrey R.

doi:10.1146/annurev.fluid.39.050905.110314

Cited by 344 publications

(324 citation statements)

References 38 publications

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“…2). Our measurements do not indicate significantly reduced mixing efficiencies within fish aggregations and the values observed (c mix < 0.2) are in close agreement with those typically found in stratified water bodies (Ivey et al 2008). Gregg and Horne (2009), in contrast, observed a reduction of mixing efficiencies within aggregations of marine animals to values of about 1% of this value.…”

Section: Factorsupporting

confidence: 91%

In situ measurements of turbulence in fish shoals

Lorkea

Probsta

2009

Limnology & Oceanography

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Turbulence was measured in situ within shoals of juvenile perch Perca fluviatilis with a self-contained autonomous microstructure profiler near an artificial reef in Lake Constance, Germany. Depth-averaged dissipation rates of turbulent kinetic energy (TKE) correlated with the density of shoaling fish, providing evidence for fish-induced turbulence in a large and stratified lake. The observed range and the depth-averaged values of TKE dissipation rates associated with fish-generated turbulence were comparable with magnitudes of turbulence typically caused by internal waves or wind forcing. Enhanced turbulence within fish shoals could only be observed during periods of low background turbulence and high fish abundance. The observed rates of dissipation of TKE are about two orders of magnitude smaller than production rates of TKE estimated from empirical models on the basis of observed fish size and swimming speed.

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Section: Factorsupporting

confidence: 91%

In situ measurements of turbulence in fish shoals

Lorkea

Probsta

2009

Limnology & Oceanography

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“…8 are presented several renderings of a thin x-z slab, zooming in on an area of 0.12 × 0.1 times the box size, comparable to the vertical Taylor scale. Note that OZ is about 1 3 of this slab size. These visualizations show scales at which overturning can occur and demonstrate the clear onset of Kelvin-Helmholtz instabilities due to shear layers.…”

Section: Structuresmentioning

confidence: 99%

“…Other dimensionless parameters, combinations or variants of these basic ones, are commonly defined as well (see §II [1] and references therein). Indeed, at R B = 1, the Ozmidov scale…”

Section: Introductionmentioning

confidence: 99%

Evidence for Bolgiano-Obukhov scaling in rotating stratified turbulence using high-resolution direct numerical simulations

et al. 2015

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We report results on rotating stratified turbulence in the absence of forcing, with large-scale isotropic initial conditions, using direct numerical simulations computed on grids of up to 4096 3 points. The Reynolds and Froude numbers are respectively equal to Re = 5.4×10 4 and F r = 0.0242. The ratio of the Brunt-Väisälä to the inertial wave frequency, N/f , is taken to be equal to 4.95, a choice appropriate to model the dynamics of the southern abyssal ocean at mid latitudes. This gives a global buoyancy Reynolds number RB = ReF r 2 = 32, a value sufficient for some isotropy to be recovered in the small scales beyond the Ozmidov scale, but still moderate enough that the intermediate scales where waves are prevalent are well resolved. We concentrate on the largescale dynamics, for which we find a spectrum compatible with the Bolgiano-Obukhov scaling, and confirm that the Froude number based on a typical vertical length scale is of order unity, with strong gradients in the vertical. Two characteristic scales emerge from this computation, and are identified from sharp variations in the spectral distribution of either total energy or helicity. A spectral break is also observed at a scale at which the partition of energy between the kinetic and potential modes changes abruptly, and beyond which a Kolmogorov-like spectrum recovers. Large slanted layers are ubiquitous in the flow in the velocity and temperature fields, with local overturning events indicated by small Richardson numbers, and a small large-scale enhancement of energy directly attributable to the effect of rotation is also observed.

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“…As an example, internal gravity waves arising from it are responsible for transfer of momentum between different regions of the atmosphere [2], and for transport in the oceans [3,4]. Much effort has been put in characterizing internal gravity waves and their relation with geophysical flows [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Absorption of waves by large-scale winds in stratified turbulence

Leoni

Mininni

2015

Phys. Rev. E

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The atmosphere is a nonlinear stratified fluid in which internal gravity waves are present. These waves interact with the flow, resulting in wave turbulence that displays important differences with the turbulence observed in isotropic and homogeneous flows. We study numerically the role of these waves and their interaction with the large scale flow, consisting of vertically sheared horizontal winds. We calculate their space and time resolved energy spectrum (a four-dimensional spectrum), and show that most of the energy is concentrated along a dispersion relation that is Doppler shifted by the horizontal winds. We also observe that when uniform winds are let to develop in each horizontal layer of the flow, waves whose phase velocity is equal to the horizontal wind speed have negligible energy. This indicates a nonlocal transfer of their energy to the mean flow. Both phenomena, the Doppler shift and the absorption of waves traveling with the wind speed, are not accounted for in current theories of stratified wave turbulence.

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Density Stratification, Turbulence, but How Much Mixing?

Cited by 344 publications

References 38 publications

In situ measurements of turbulence in fish shoals

In situ measurements of turbulence in fish shoals

Evidence for Bolgiano-Obukhov scaling in rotating stratified turbulence using high-resolution direct numerical simulations

Absorption of waves by large-scale winds in stratified turbulence

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