Boundary mixing in a small stratified lake

Hondzo, Miki; Haider, Ziaul

doi:10.1029/2002wr001851

Cited by 22 publications

(16 citation statements)

References 26 publications

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“…Scalars with high Schmidt number can experience enhanced mixing at low «/nN 2 , while scalars with lower Schmidt number are transported by molecular diffusion. Differences between the thermal and haline eddy diffusivities Imberger and Ivey (1991) ◁ Boundary mixing (small lake) Hondzo and Haider (2004) ◄ Benthic boundary layer (Kinneret) Lemckert and Imberger (1998) ✰ Benthic boundary layer (Biwa) Lemckert and Imberger (1998) made the eddy diffusivity of density depend on the density ratio.…”

Section: Discussionmentioning

confidence: 99%

“…However, in the present experiments, the scalar eddy diffusivities at «/nN 2 5 7 are nearly two and four orders of magnitude greater than the molecular diffusivities for temperature and salinity, respectively. Previous estimates of the maximum value of «/nN 2 for the diffusive regime vary from 1 to 30 with a typical value of 15 (e.g., Ivey et al 2000;Gibson 1980;Hondzo and Haider 2004 (Fig. 6), which implies R f ' 0.2, or approximately the maximum value of R f typically used in oceanography (Osborn 1980).…”

Section: /2mentioning

confidence: 99%

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Experiments on Differential Scalar Mixing in Turbulence in a Sheared, Stratified Flow

Jackson

Rehmann

2014

Journal of Physical Oceanography

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Laboratory experiments were performed to measure differential diffusion of temperature and salinity across a sheared density interface. The eddy diffusivity of temperature K T exceeded the eddy diffusivity of salinity K S by as much as 1.5 orders of magnitude at low «/nN 2 , where « is the rate of dissipation of turbulent kinetic energy, n is the kinematic viscosity, and N is the buoyancy frequency in the pycnocline. The diffusivity ratio d 5 K S /K T increased from about 0.05 to 1 over the range 0.1 , «/nN 2 , 40. These differences made the eddy diffusivity of density depend on the density ratio. The trend of d with «/nN 2 was consistent with trends found in other experiments, simulations, and theory, and the collapse of several datasets allowed the diffusivity ratio to be expressed as a function of «/nN 2 . However, shear decreased differential diffusion less in the experiments than predicted by theory for homogeneous turbulence subjected to constant shear and stratification. No strong effect of the density ratio on the diffusivity ratio was apparent. Because many flows in oceanography and limnology have values of «/nN 2 low enough to exhibit significant differential diffusion, accounting for differential diffusion in interpreting measurements and modeling stratified water bodies is recommended.

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Section: Discussionmentioning

confidence: 99%

Section: /2mentioning

confidence: 99%

Experiments on Differential Scalar Mixing in Turbulence in a Sheared, Stratified Flow

Jackson

Rehmann

2014

Journal of Physical Oceanography

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“…The Batchelor wave number is a function of the TKE dissipation rate (Batchelor 1959). Temperature microstructure measurements are a common approach for quantifying turbulence and turbulent mixing, particularly in the low-energetic environment of lakes and reservoirs (Imberger and Ivey 1991;Lorke et al 2003;Hondzo and Haider 2004). Dissipation rates of TKE e were estimated for profile segments of 0.5-m length by applying a maximum-likelihood fitting technique (Ruddick et al 2000) on the respective temperature gradient spectra.…”

Section: Methodsmentioning

confidence: 99%

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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“…Critical reflection of internal waves from sloping bottom topography was observed by Eriksen [1982, 1998] and was studied theoretically ( Thorpe [1999] provided a recent review). The production of turbulence by breaking internal waves on slopes and hence their potential contribution to boundary mixing processes was studied in the laboratory [ Boegman et al , 2005a; Helfrich , 1992; Ivey and Nokes , 1989] as well as numerically [ Javam et al , 1999; Slinn and Riley , 1996] and enhanced turbulence near boundaries is frequently observed in lakes [ Hondzo and Haider , 2004; MacIntyre et al , 1999] as well as in the ocean [ Ledwell et al , 2000; Moum et al , 2002; Rudnick et al , 2003]. The sparse spatial and temporal resolution of turbulence measurements in the field, which are usually performed using profiling or towed instrument packages, however, do not allow to highlight the contribution of internal wave breaking to the enhanced bottom boundary layer turbulence.…”

Section: Introductionmentioning

confidence: 99%

Boundary mixing in the thermocline of a large lake

Lorke

2007

J. Geophys. Res.

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[1] High-resolution measurements of near-bottom temperature stratification and current velocity were performed on the sloping boundary of a large lake at the depth of the seasonal thermocline. The measurements cover nearly the entire stratified period and reveal the periodic occurrence of strong temperature and current velocity fluctuations, which can be attributed to shoaling high-frequency internal waves with periods between 5 and 20 min. Two different techniques are applied to obtain a long-term record of dissipation rates of turbulent kinetic energy from the current velocity measurements. Shoaling of high-frequency internal waves is associated with a strong and rapid increase of turbulent dissipation rates of up to four orders of magnitude. Since the occurrence of high-frequency internal waves on the slope is correlated with the passage of the dominant basin-scale internal Kelvin wave with a period of four days, energy dissipation rates on the slope vary with the same period. Diapycnal diffusivities, estimated by combining the dissipation estimates with simultaneously measured density stratification, follow a similar dynamics and a comparison with a basin-scale diffusivity estimate based on tracer measurements reveal the importance of boundary mixing, which, at this particular site, is mainly driven by the interaction of high-frequency internal waves with the sloping boundary.

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Boundary mixing in a small stratified lake

Cited by 22 publications

References 26 publications

Experiments on Differential Scalar Mixing in Turbulence in a Sheared, Stratified Flow

Experiments on Differential Scalar Mixing in Turbulence in a Sheared, Stratified Flow

In situ measurements of turbulence in fish shoals

Boundary mixing in the thermocline of a large lake

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