Mixing efficiency in stably stratified growing turbulence

Rohr, Jim; Atta, Charles Van

doi:10.1029/jc092ic05p05481

Cited by 45 publications

(28 citation statements)

References 21 publications

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“…It is also possible to compare the mixing with that due to shear-generated turbulence, without appeal to wave effects. work, in which surface waves are absent [e.g., Rohr and Van Atta, 1987]. The CL2 theory is appealing for the relative ease with which the relevant parameters can be estimated.…”

Section: Discussionmentioning

confidence: 99%

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Observed growth of Langmuir circulation

Smith¹

1992

J. Geophys. Res.

118

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Surface velocity patterns and upper ocean density profiles are presented from a period following a sudden increase in wind. A prior wind speed of 8 m/s failed to produce visible signs of Langmuir circulation. After the wind speed increased to 13 m/s, Langmuir circulation developed within 15 min. The initial scale observed was about 16 m, streak to streak, and may have been restricted by the depth scale of the measurements. This spacing is about two thirds of the dominant wavelength (4-s-period waves). The streak spacing (two cell widths) increased at roughly 40 m/h for the next hour. The density measurements indicate a depth of mixing which increased over the same period at a rate of 20 m/h; thus the vertical to horizontal aspect ratio was about 1:1. Prior stratification was weak (buoyancy frequency of about 1.5 cph), and probably did not affect the circulation initially.

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Section: Discussionmentioning

confidence: 99%

“…0148-0227/92/91JC=03118$05.00 wind-induced surface shear layer. Much of what is known in this case is derived from laboratory experiments [e.g., Rohr and Van Atta, 1987]. (3) Circulation of similar form can also arise as an instability of an Ekman layer [e.g., Leibovich and Lele, 1985].…”

Section: Introductionmentioning

confidence: 99%

Observed growth of Langmuir circulation

Smith¹

1992

J. Geophys. Res.

118

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“…The results can also be cast in terms of Ri, which is discussed below. experiments, numerical and field studies [20,32,69,[74][75][76]. Lozovatsky et al [31] proposed an approximation, 4) to the GISS modelling results of Canuto et al [36], in which the eddy coefficients are parametrized using specific damping functions.…”

Section: Dependence Of Mixing Reynolds Numbers R Mχ and R Mf On Rimentioning

confidence: 99%

Mixing efficiency in natural flows

Lozovatsky

Fernando

2013

Phil. Trans. R. Soc. A.

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It is argued that the mixing efficiency of naturally occurring stratified shear flows, γ = Rf /(1− Rf ), where Rf is the flux Richardson number, is dependent on at least two governing parameters: the gradient Richardson number Ri and the buoyancy Reynolds number Re b = ε / vN 2 . It is found that, in the range approximately 0.03< Ri <0.4, which spans 10 4 < Re b <10 6 , the mixing efficiency obtained via direct measurements of fluxes and property gradients in the stable atmospheric boundary layer and homogeneous/stationary balance equations of turbulent kinetic energy (TKE) is nominally similar to that evaluated using the scalar balance equations. Outside these Ri and Re b ranges, the commonly used flux-estimation methodology based on homogeneity and stationarity of TKE equations breaks down (e.g. buoyancy effects are unimportant, energy flux divergence is significant or flow is non-stationary). In a wide range, 0.002< Ri <1, the mixing efficiency increases with Ri , but decreases with Re b . When Ri is in the proximity of Ri cr ∼0.1–0.25, γ can be considered a constant γ ≈0.16–0.2. The results shed light on the wide variability of γ noted in previous studies.

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“…Rohr and Van Atta, 1987;Ivey and Imberger, 1991), direct numerical simulations (e.g. Smyth et al, 2001) or theoretical considerations (Weinstock, 1992), suggest that R f (and thus γ ) evolves during the life cycle of the turbulence event.…”

Section: The Dissipation Rates Ratiomentioning

confidence: 99%

Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review

Wilson¹

2004

Ann. Geophys.

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Abstract. The actual impact on vertical transport of smallscale turbulence in the free atmosphere is still a debated issue. Numerous estimates of an eddy diffusivity exist, clearly showing a lack of consensus. MST radars were, and continue to be, very useful for studying atmospheric turbulence, as radar measurements allow one to estimate the dissipation rates of energy (kinetic and potential) associated with turbulent events. The two commonly used methods for estimating the dissipation rates, from the backscattered power and from the Doppler width, are discussed. The inference methods of a local diffusivity (local meaning here "within" the turbulent patch) by using the dissipation rates are reviewed, with some of the uncertainty causes being stressed. Climatological results of turbulence diffusivity inferred from radar measurements are reviewed and compared.As revealed by high resolution MST radar measurements, atmospheric turbulence is intermittent in space and time. Recent theoretical works suggest that the effective diffusivity of such a patchy turbulence is related to statistical parameters describing the morphology of turbulent events: filling factor, lifetime and height of the patches. It thus appears that a statistical description of the turbulent patches' characteristics is required in order to evaluate and parameterize the actual impact of small-scale turbulence on transport of energy and materials. Clearly, MST radars could be an essential tool in that matter.

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Mixing efficiency in stably stratified growing turbulence

Cited by 45 publications

References 21 publications

Observed growth of Langmuir circulation

Observed growth of Langmuir circulation

Mixing efficiency in natural flows

Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review

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