An Evaluation of χT Estimation Techniques: Implications for Batchelor Fitting and ɛ

Steinbuck, Jonah V.; Stacey, Mark T.; Monismith, Stephen G.

doi:10.1175/2009jtecho611.1

Cited by 27 publications

(37 citation statements)

References 34 publications

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“…Rate of dissipation and vertical diffusivity: The rate of dissipation of turbulent kinetic energy e was computed from the SCAMP data by fitting the measured temperature gradient spectra to the theoretical Batchelor spectrum using 25-cm segments and the maximum-likelihood spectralfitting method developed by Ruddick et al (2000; and recently improved by Steinbuck et al [2009]). These methods provide a good fit to the theoretical Batchelor spectrum and give reliable criteria to reject bad segments.…”

Section: Methodsmentioning

confidence: 99%

Poincaré wave–induced mixing in a large lake

Bouffard¹,

Boegman²,

Rao

2012

Limnology & Oceanography

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A 10,000-km 2 hypoxic 'dead zone' forms, during most years, in the central basin of Lake Erie. To investigate the processes driving the hypoxia, we conducted a 2-yr field campaign where the mixing in the lake interior during the stratification period was examined using current meters and temperature-loggers data, as well as . 600 temperature microstructure profiles, from which turbulent mixing was computed. Near-inertial Poincaré waves drive shear instability, generating , 1-m amplitude and 10-m wavelength high-frequency internal waves with , 1-m density overturns that lead to an increase in turbulent dissipation by one order of magnitude. The instabilities are associated with enhanced vertical shear at the crests and troughs of the Poincaré waves and may be correlated with the local gradient Richardson number. Poincaré wave-induced mixing should be an important factor when the Burger number , 0.25. The strong diapycnal mixing induced by the Poincaré wave activity will also significantly modify the energy-flux paths. For example, we estimate that, in Lake Erie, 0.85% of the wind energy is transferred to the lake interior (below the surface layer); of this, 40% is dissipated in the interior metalimnion and 60% is dissipated at the bottom boundary. In smaller lakes, 0.42% of wind energy is transferred to the deeper water, with 90% dissipated in the boundary and 10% in the interior metalimnion.

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Section: Methodsmentioning

confidence: 99%

Poincaré wave–induced mixing in a large lake

Bouffard¹,

Boegman²,

Rao

2012

Limnology & Oceanography

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“…We followed the standard methods of Luketina and Imberger (2001) and Ruddick et al (2000) to calculate x and the turbulent kinetic energy dissipation, e, by fitting the Batchelor spectrum to temperature microstructure data from each segment. To improve handling of noise contamination during Batchelor curve-fitting, the calculation method for x and e followed the modifications suggested by Steinbuck et al (2009). Poor Batchelor fits were identified using the spectral fit criteria of Ruddick et al (2000), thus:…”

Section: Methodsmentioning

confidence: 99%

Effects of seasonal stratification on turbulent mixing in a hypereutrophic coastal lagoon

Cousins

Stacey

Drake

2009

Limnology & Oceanography

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Seasonal variations in vertical turbulent mixing rates, density structure, inorganic nutrient concentrations, and phytoplankton biomass were investigated in a shallow, tidally choked coastal lagoon. The project site, Rodeo Lagoon, is located in the Golden Gate National Recreation Area, California, and has experienced intense blooms of the cyanobacteria Nodularia spumigena and Microcystis aeruginosa in recent years. Monthly measurements collected along a transect of the lagoon from March 2006 to April 2008 show it is strongly stratified by brackish water in winter, when freshwater inputs from the watershed and saltwater inputs from storm surge are both at their highest. The squared buoyancy frequency exceeds 0.5 s 22 under these conditions. In summer, weaker diurnal temperature stratification is the result of strong light absorption characteristics in this hypereutrophic lagoon. Wind is the dominant driver of turbulent mixing. Although water depths of less than 2.5 m lead to the expectation of rapid vertical mixing, limited fetch and strong density gradients reduce the coupling of wind stress and bottom stress. The vertical turbulent diffusivity is reduced by as much as three orders of magnitude across the pycnocline, and the water column in and below the pycnocline shows active turbulence only intermittently. The annual cycle of salt-based stratification and accompanying reduction in turbulent exchange of nutrients between the sediments and overlying water column inhibit the flushing of nutrients out of the lagoon and contribute to excessive phytoplankton biomass.

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“…-including the improvement on the estimation of χ T ( • C 2 s −1 ) (the rate of destruction of temperature variance by molecular diffusion) proposed by Steinbuck et al (2009). variance.…”

Section: Dissipation Measurements and K Z Estimatesmentioning

confidence: 99%

Characterization of turbulence from a fine-scale parameterization and microstructure measurements in the Mediterranean Sea during the BOUM experiment

Cuypers

Bouruet‐Aubertot

Marec³

et al. 2012

Biogeosciences

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Abstract.One of the main purposes of the BOUM experiment was to find evidence of the possible impact of submesoscale dynamics on biogeochemical cycles. To this aim physical as well as biogeochemical data were collected along a zonal transect through the western and eastern basins of the Mediterranean Sea. Along this transect 3-day fixed point stations were performed within anticyclonic eddies during which microstructure measurements of the temperature gradient were collected over the top 100 m of the water column. We focus here on the characterization of turbulent mixing. The analysis of microstructure measurements revealed a high level of turbulent kinetic energy (TKE) dissipation rate in the seasonal pycnocline and a moderate level below with mean values of the order of 10 −6 W kg −1 and 10 −8 W kg −1 , respectively. The Gregg Henyey (Gregg, 1989) fine-scale parameterization of TKE dissipation rate produced by internal wave breaking, and adapted here following Polzin et al. (1995) to take into account the strain to shear ratio, was first compared to these direct measurements with favorable results. The parameterization was then applied to the whole data set. Within the eddies, a significant increase of dissipation at the top and base of eddies associated with strong near-inertial waves is observed. Vertical turbulent diffusivity is increased both in these regions and in the weakly stratified eddy core. The stations collected along the East-West transect provide an overview of parameterized TKE dissipation rates and vertical turbulent diffusivity over a latitudinal section of the Mediterranean Sea. Strong TKE dissipation rates are found within the first 500 m and up to 1500 m above the bottom. Close to the bottom where the stratification is weak, the inferred vertical turbulent diffusivity can reach K z 10 −3 m 2 s −1 and may therefore have a strong impact on the upward diffusive transport of deep waters masses.

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An Evaluation of χT Estimation Techniques: Implications for Batchelor Fitting and ɛ

Cited by 27 publications

References 34 publications

Poincaré wave–induced mixing in a large lake

Poincaré wave–induced mixing in a large lake

Effects of seasonal stratification on turbulent mixing in a hypereutrophic coastal lagoon

Characterization of turbulence from a fine-scale parameterization and microstructure measurements in the Mediterranean Sea during the BOUM experiment

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