On the Accuracy of Overturn-Based Estimates of Turbulent Dissipation at Rough Topography

On the Accuracy of Overturn-Based Estimates of Turbulent Dissipation at Rough Topography AbstractEvidence in support of overturn-based methods, often used to infer turbulent dissipation rate from density profiles, is typically from regions with weaker turbulence than that at rough-topography hotspots. The present work uses direct numerical simulations (DNS) of an idealized problem of sloping topography as well as high-resolution large-eddy simulation (LES) of turbulent flow at more realistic topography in order to investigate the accuracy of overturn-based methods in sites with internal wave breaking. Two methods are assessed: Thorpe sorting, where the overturn length LT is based on local distortion of measured density from the background, and inversion sorting, where the inversion length scale LI measures the statically unstable local region. The overturn boundaries are different between the two methods. Thorpe sorting leads to an order of magnitude overestimate of the turbulent dissipation in the DNS during large convective overturn events when inversion sorting is more accurate. The LES of steep, realistic topography leads to a similar conclusion of a substantial overestimate of dissipation by Thorpe sorting. Energy arguments explain the better performance of inversion sorting in convectively driven turbulence and the better performance of Thorpe sorting in shear-driven turbulence. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Physical Oceanography American Meteorological Society

On the Accuracy of Overturn-Based Estimates of Turbulent Dissipation at Rough Topography

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0485
eISSN
1520-0485
D.O.I.
10.1175/JPO-D-15-0169.1
Publisher site
See Article on Publisher Site

Abstract

AbstractEvidence in support of overturn-based methods, often used to infer turbulent dissipation rate from density profiles, is typically from regions with weaker turbulence than that at rough-topography hotspots. The present work uses direct numerical simulations (DNS) of an idealized problem of sloping topography as well as high-resolution large-eddy simulation (LES) of turbulent flow at more realistic topography in order to investigate the accuracy of overturn-based methods in sites with internal wave breaking. Two methods are assessed: Thorpe sorting, where the overturn length LT is based on local distortion of measured density from the background, and inversion sorting, where the inversion length scale LI measures the statically unstable local region. The overturn boundaries are different between the two methods. Thorpe sorting leads to an order of magnitude overestimate of the turbulent dissipation in the DNS during large convective overturn events when inversion sorting is more accurate. The LES of steep, realistic topography leads to a similar conclusion of a substantial overestimate of dissipation by Thorpe sorting. Energy arguments explain the better performance of inversion sorting in convectively driven turbulence and the better performance of Thorpe sorting in shear-driven turbulence.

Journal

Journal of Physical OceanographyAmerican Meteorological Society

Published: Mar 28, 2017

References

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