Mixing by shear instability at high Reynolds number

Geyer, W. Rockwell; Lavery, Andone C.; Scully, Malcolm E.; Trowbridge, John

doi:10.1029/2010gl045272

Cited by 116 publications

(198 citation statements)

References 28 publications

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“…Although a different turbulence frequency range is used here given the different sampling rates, the computation of such variance has similarities with the computation of higher-frequency conductivity variance used for estuarine data 13 and the computation of temperature dissipation rate that was compared with kinetic energy dissipation rates in the upper ocean. 28 Here, the temperature variance is scaled with the local buoyancy frequency, which follows after relating isopycnals excursions, which are indicative of potential energy, to L O .…”

Section: Methodsmentioning

confidence: 99%

“…(Nonetheless, such shipborne acoustic images demonstrate very detailed overturning including secondary turbulence along the rim of the largest Kelvin-Helmholtz overturn in high Reynolds number flows in shallow seas). [12][13][14] In the present paper, case-studies are presented of particular stratified-turbulence close to, but some distance above, deep underwater topography south of New Zealand. One day, two tidal periods, of high-precision temperature sensor data are used to demonstrate spatial and temporal variability and the importance of high-frequency interfacial internal waves.…”

Section: Introductionmentioning

confidence: 99%

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Stratified turbulence and small-scale internal waves above deep-ocean topography

Haren

2013

Physics of Fluids

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When ocean's internal tidal waves "beach" at underwater topography, they transform from more or less linear into highly nonlinear waves that can break with generation of vigorous turbulent mixing. Although most mixing occurs in the half hour around a steep (bottom-)front leading the upslope moving internal tide phase, relatively large mixing also occurs some distance of several tens of meters off the bottom, just prior to the downslope moving internal tide phase and initiated by highfrequency "small-scale" internal waves. Details of this off-bottom small-scale mixing in a stratified natural environment and some of its variability per tidal period are presented here in two case studies using high-resolution temperature observations (61 sensors at 1 m intervals; <10 −3 • C precision) at a 969 m deep site south of New Zealand. The observations shed some light on stratified turbulence that is generated in a relatively thick (∼30 m) weakly stratified layer and in the strongly stratified interfaces above and below. The interfacial internal waves generate turbulence with largest dissipation rate and temperature variance at the edge of the upper interface and the weakly stratified layer. When these waves steep nonlinearly, immediate moderate turbulence generation is observed below, throughout the weakly stratified layer. Largest turbulence is generated by 25 m high asymmetric Holmboe overturns. C 2013 AIP Publishing LLC. [http://dx

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Stratified turbulence and small-scale internal waves above deep-ocean topography

Haren

2013

Physics of Fluids

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“…For certain shallow highly stratified or partially mixed estuaries, one may expect that most of the dissipation is determined by bottom stress and stress in the pycnocline (e.g. Geyer and Smith, 1987;Geyer et al, 2000Geyer et al, , 2010. In these estuaries, the stratification varies within a broad range of values between ebb and flood conditions with often very weak stratification during strongest tidal flow (e.g.…”

Section: Boundary Mixing In the Lslementioning

confidence: 99%

Behavior and mixing of a cold intermediate layer near a sloping boundary

2015

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As in many other subarctic basins, a cold intermediate layer (CIL) is found during ice-free months in the Lower St. Lawrence Estuary (LSLE), Canada. This study examines the behavior of the CIL above the sloping bottom using a high resolution mooring deployed on the northern side of the estuary. Observations show successive swashes/backwashes of the CIL on the slope at a semi-diurnal frequency. It is shown that these upslope and downslope motions are likely caused by internal tides generated at the nearby channel head sill. Quantification of mixing from 322 turbulence casts reveals that in the bottom 10 m of the water column, the timeaverage dissipation rate of turbulent kinetic energy is ǫ 10 m = 1.6 × 10 −7 W kg −1 , an order of magnitude greater than found in the interior of the basin, far from boundaries. Near-bottom dissipation during the flood phase of the M 2 tide cycle (upslope flow) is about four times greater than during the ebb phase (downslope flow). Bottom shear stress, shear instabilities and internal wave scattering are considered as potential boundary mixing mechanisms near the seabed. In the interior of the water column, far from the bottom, increasing dissipation rates are observed with both increasing stratification and shear, which suggests some control of the dissipation by the internal wave field. However, poor fits with a parametrization for large-scale wave-wave interactions suggests that the mixing is partly driven by more complex non-linear and/or smaller scale waves.Frédéric Cyr Institut des sciences de la mer de Rimouski, Université du Québecà Rimouski, Rimouski (Québec) Canada.

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“…Of particular interest are 1) the effects of turbulence anisotropy on the effective refractive index fluctuations, as the refractive index fluctuations can be related to turbulence parameters, such as the dissipation rate of turbulent kinetic energy, under some conditions, 2) the presence and influence of coherent 3-D wave structures and shear instabilities generated in highly sheared, high-Reynolds number environments [9,10].…”

Section: Approachmentioning

confidence: 99%

“…The choice of the CT River is motivated partly by the physics of the flow (highly stratified and energetic), as well as by the potential for capitalizing on the research already conducted at this location (measurements funded in part by ONR Physical Oceanography in 2008 and 2009). These previous field measurements were focused on measuring and understanding high-frequency broadband acoustic backscattering in highly-stratified, energetic estuarine environments together with direct microstructure measurements [9,10]. The measurements already performed at this field site provide significant insight into the expected flow regimes, with shear instabilities representing a dominant mechanisms leading to mixing during certain times of the ebb tide ( Figure 5), and potentially leading to significant variability in the scintillation arrivals.…”

Section: -Dimensional Angle Of Arrivalmentioning

confidence: 99%

High-Frequency Acoustic Propagation in Shallow, Energetic, Highly-Salt-Stratified Environments

Lavery¹,

Farmer²

2012

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LONG-TERM GOALSThe long term goal of this research is to measure and understand high-frequency, line-of-sight acoustic propagation in an estuarine environment characterized by strong tidal flow, often large salinity stratification, high shear, high dissipation rates of turbulent kinetic energy, shear instabilities, and increased water property variability. OBJECTIVESAcoustic propagation techniques provide a means for remote-sensing of the path-averaged statistical structure and motion of the intervening flow, providing information on the 2-dimensional characteristics of turbulence, microstructure, and advection. Estuaries provide an excellent environment to quantify stratified turbulence and its influence on acoustic propagation as a broad range of stratification and turbulence intensities are encountered within a single tidal cycle.The primary objective is to conduct high-frequency (120 kHz), line-of-sight acoustic propagation measurements from 29 October to 2 November, 2012 in the Connecticut (CT) River estuary. In addition, measurements of high-frequency broadband acoustic backscattering (30 -600 kHz), currents (using a 1.2 MHz ADCP), suspended sediment concentrations, fluorescence, and continuous conductivity, temperature, and depth (CTD) measurements will be performed in order to support the interpretation of the scintillation data. Secondary objectives include testing the validity of the existing theoretical framework for propagation of high-frequency sound through a highly turbulent medium,

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Mixing by shear instability at high Reynolds number

Cited by 116 publications

References 28 publications

Stratified turbulence and small-scale internal waves above deep-ocean topography

Stratified turbulence and small-scale internal waves above deep-ocean topography

Behavior and mixing of a cold intermediate layer near a sloping boundary

High-Frequency Acoustic Propagation in Shallow, Energetic, Highly-Salt-Stratified Environments

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