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Environmental Fluid Mechanics

, Volume 13, Issue 3, pp 205–226 | Cite as

Observed relationships between microstructure patches and the gradient Richardson number in a thermally stratified lake

  • Peter S. Yeates
  • Andrés Gómez-Giraldo
  • Jörg Imberger
Original Article

Abstract

Microstructure profiles of velocity and temperature were collected in Lake Kinneret during the summer months of 1997, 1998, 1999 and 2001 using the Portable Flux Profiler. The profiles were analysed to determine the turbulent properties within statistically homogeneous microstructure patches that were identified in each profile. The nature of the turbulent properties and their distribution is discussed in terms of the dominant forcing mechanisms that exist through the water column. It was found that the properties of binned patch data collapsed reasonably into log-linear functions of the gradient Richardson number \(Ri_{g}\) with changes in behaviour at \(Ri_{g} = 0.03\) and 0.2. For \(Ri_{g} < 0.03\) the observations were dominated by boundary turbulence and law-of-the-wall approximations were shown to provide a good description of the observed data near the lake surface. For 0.03 \(<Ri_{g} < 0.2\) the microstructure appeared to represent turbulence generated primarily by shear instabilities in the interior of the lake that were sampled at various stages of their evolution from the initial stages of development at critical \(Ri_{g} \sim \) 0.2, where buoyancy frequency and internal shear peak. In terms of the mixing that results from the observed turbulence, both regimes suggest that mixing efficiency \(\gamma _{mix}\) falls in a relatively narrow range from 0.07 to 0.16 over the large range 10\(^{-5} \!<\! Ri_{g} \!<\! 0.2\). For supercritical \(Ri_{g}\), shear weakened and turbulence was dominated by strong buoyancy forces so that mixing was suppressed and \(\gamma _{mix}\) decreased rapidly toward zero.

Keywords

Stratification Turbulence Mixing and eddy diffusivity 

Notes

Acknowledgments

We thank the staff at the Kinneret Limnological Laboratory (KLL) and the Centre for Water Research for assistance with the field experiments and data processing. The Centre for Environmental Fluid Dynamics and the Israeli Water Commission funded the experiments. We thank Jason Antenucci, José Romero, Chris Dallimore and Iossif Lozovatsky and the editors and reviewers for their comments on the manuscript. Andrés Gómez-Giraldo acknowledges an International Postgraduate Scholarship and an ad-hoc Centre for Water Research scholarship. This is Centre for Water Research reference ED1641PY.

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Peter S. Yeates
    • 1
  • Andrés Gómez-Giraldo
    • 1
    • 2
  • Jörg Imberger
    • 1
  1. 1.Centre for Water ResearchUniversity of Western AustraliaCrawleyAustralia
  2. 2.Department of Geosciences and EnvironmentUniversidad Nacional de ColombiaMedellinColombia

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