Observation and analysis of shear instability in the Fraser River estuary

Tedford, Edmund W.; Carpenter, Jeffrey R.; Pawlowicz, Rich; Pieters, Roger; Lawrence, Gregory A.

doi:10.1029/2009jc005313

Cited by 75 publications

(64 citation statements)

References 31 publications

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“…These observations are consistent with asymmetric Holmboe instabilities as found in direct numerical simulations, 16 and as observed in Fraser River estuary. 32 Here, the first 200 s of each Holmboe passage show the largest discrepancy between vertical averages of HF-temperature variance and dissipation rate estimates (Figure 6(d)). In depth-time, largest temperature variance is observed along the interface mainly, but more focused on the center of the braid between two Holmboe instabilities ( Figure 6(c)).…”

Section: Observationsmentioning

confidence: 99%

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: Observationsmentioning

confidence: 99%

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

Haren

2013

Physics of Fluids

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“…In subsequent work, field measurements were used to explore the intratidal variability, seasonal progression, and mixing of both strongly and weakly forced salt wedges [e.g., Geyer and Farmer , 1989; Guerrero et al 1997; Ibañez et al , 1997]. Most recently, advances in measurement techniques has allowed more detailed examination of the vertical and lateral structure of salt wedges, particularly vertical mixing [e.g., Geyer et al , 2008b; Tedford et al , 2009].…”

Section: Introductionmentioning

confidence: 99%

“…In addition, in a strongly forced salt wedge estuary, strong enough shears can develop to lead to turbulence production along the salt wedge interface. This highlights an important difference between partially mixed and strongly forced, strongly stratified estuaries: partially mixed estuaries tend to be dominated by bottom boundary layer generated turbulence [e.g., Peters , 1997; Stacey et al , 1999b] while for strongly stratified estuaries mixing, i.e., buoyancy flux, may be driven strongly by interfacial shear, particularly during ebb tides [e.g., Geyer and Farmer , 1989; Geyer et al , 2008b; MacDonald and Horner ‐ Devine , 2008; Partch and Smith , 1978; Tedford et al , 2009]. The interaction of this temporal variation in vertical mixing with stratification in a salt wedge estuary is one focus of this paper.…”

Section: Introductionmentioning

confidence: 99%

Role of straining and advection in the intratidal evolution of stratification, vertical mixing, and longitudinal dispersion of a shallow, macrotidal, salt wedge estuary

Giddings¹,

Fong²,

Monismith³

2011

J. Geophys. Res.

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[1] A month of flow observations in the Snohomish River Estuary reveals the complex intratidal and fortnightly stratification, mixing, and dispersion dynamics in this macrotidal, shallow, salt wedge estuary system. Both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries. Bottom-generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides. This bottom-generated mixing contributes to a buoyancy flux near the top of a well-mixed layer during strong flood tides. During strong ebb tides, interfacial shear production and buoyancy flux occur along the sharp straining-enhanced interface just before the system becomes well mixed. Longitudinal dispersion is less sensitive to the spring/neap cycle yet exhibits strong intratidal variability. Reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle, behavior we attribute to a lack of vertical shear. Overall, ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing. Intratidal variability, which varies on the spring/neap scale, is a dominant feature of this estuary, suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified, strongly forced estuaries.Citation: Giddings, S. N., D. A. Fong, and S. G. Monismith (2011), Role of straining and advection in the intratidal evolution of stratification, vertical mixing, and longitudinal dispersion of a shallow, macrotidal, salt wedge estuary,

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“…Examples include the numerous analytical studies discussed by Drazin and Reid (1981); a numerical investigation of several idealized but important shear profiles (Hazel 1972); observations and analysis of shear instabilities in the atmospheric boundary layer (e.g., De Baas and Driedonks 1985); the ocean (e.g., Sun et al 1998;Smyth et al 2011), and estuarine flows (e.g., Tedford et al 2009); and distinguishing Kelvin-Helmholtz waves from Holmboe waves (Carpenter et al 2010). In addition, slightly modified forms of the TG equation have been used in numerical studies of atmospheric wave generation by shear Mastrantonio et al 1976;Mobbs and Darby 1989).…”

Section: Introductionmentioning

confidence: 98%

A General Numerical Method for Analyzing the Linear Stability of Stratified Parallel Shear Flows

Rees

Monahan

2014

Journal of Atmospheric and Oceanic Technology

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The stability analysis of stratified parallel shear flows is fundamental to investigations of the onset of turbulence in atmospheric and oceanic datasets. The stability analysis is performed by considering the behavior of small-amplitude waves, which is governed by the Taylor-Goldstein (TG) equation. The TG equation is a singular second-order eigenvalue problem, whose solutions, for all but the simplest background stratification and shear profiles, must be computed numerically. Accurate numerical solutions require that particular care be taken in the vicinity of critical layers resulting from the singular nature of the equation. Here a numerical method is presented for finding unstable modes of the TG equation, which calculates eigenvalues by combining numerical solutions with analytical approximations across critical layers. The accuracy of this method is assessed by comparison to the small number of stratification and shear profiles for which analytical solutions exist. New stability results from perturbations to some of these profiles are also obtained.

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Observation and analysis of shear instability in the Fraser River estuary

Cited by 75 publications

References 31 publications

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

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

Role of straining and advection in the intratidal evolution of stratification, vertical mixing, and longitudinal dispersion of a shallow, macrotidal, salt wedge estuary

A General Numerical Method for Analyzing the Linear Stability of Stratified Parallel Shear Flows

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