Diapycnal Transport and Mixing Efficiency in Stratified Boundary Layers near Sloping TopographySource: Journal of Physical Oceanography:;2010:;Volume( 041 ):;issue: 002::page 329DOI: 10.1175/2010JPO4438.1Publisher: American Meteorological Society
Abstract: The interaction of shear, stratification, and turbulence in boundary layers on sloping topography is investigated with the help of an idealized theoretical model, assuming uniform bottom slope and homogeneity in the upslope direction. It is shown theoretically that the irreversible vertical buoyancy flux generated in the boundary layer is directly proportional to the molecular destruction rate of small-scale buoyancy variance, which can be inferred, for example, from microstructure observations. Dimensional analysis of the equations shows that, for harmonic boundary layer forcing and no rotation, the problem is governed by three nondimensional parameters (slope angle, roughness number, and ratio of forcing and buoyancy frequencies). Solution of the equations with a second-moment closure model for the turbulent fluxes reveals the periodic generation of gravitationally unstable boundary layers during upslope flow, consistent with available observations. Investigation of the nondimensional parameter space with the help of this model illustrates a systematic increase of the bulk mixing efficiencies for (i) steep slopes and (ii) low-frequency forcing. Except for very steep slopes, mixing efficiencies are substantially smaller than the classical value of Γ = 0.2.
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contributor author | Umlauf, Lars | |
contributor author | Burchard, Hans | |
date accessioned | 2017-06-09T16:36:58Z | |
date available | 2017-06-09T16:36:58Z | |
date copyright | 2011/02/01 | |
date issued | 2010 | |
identifier issn | 0022-3670 | |
identifier other | ams-70985.pdf | |
identifier uri | http://onlinelibrary.yabesh.ir/handle/yetl/4212826 | |
description abstract | The interaction of shear, stratification, and turbulence in boundary layers on sloping topography is investigated with the help of an idealized theoretical model, assuming uniform bottom slope and homogeneity in the upslope direction. It is shown theoretically that the irreversible vertical buoyancy flux generated in the boundary layer is directly proportional to the molecular destruction rate of small-scale buoyancy variance, which can be inferred, for example, from microstructure observations. Dimensional analysis of the equations shows that, for harmonic boundary layer forcing and no rotation, the problem is governed by three nondimensional parameters (slope angle, roughness number, and ratio of forcing and buoyancy frequencies). Solution of the equations with a second-moment closure model for the turbulent fluxes reveals the periodic generation of gravitationally unstable boundary layers during upslope flow, consistent with available observations. Investigation of the nondimensional parameter space with the help of this model illustrates a systematic increase of the bulk mixing efficiencies for (i) steep slopes and (ii) low-frequency forcing. Except for very steep slopes, mixing efficiencies are substantially smaller than the classical value of Γ = 0.2. | |
publisher | American Meteorological Society | |
title | Diapycnal Transport and Mixing Efficiency in Stratified Boundary Layers near Sloping Topography | |
type | Journal Paper | |
journal volume | 41 | |
journal issue | 2 | |
journal title | Journal of Physical Oceanography | |
identifier doi | 10.1175/2010JPO4438.1 | |
journal fristpage | 329 | |
journal lastpage | 345 | |
tree | Journal of Physical Oceanography:;2010:;Volume( 041 ):;issue: 002 | |
contenttype | Fulltext |