Open AccessParameterizing individual effects of shear and stratification on mixing in stably stratified shear flows
Author(s) -
Shimizu Kenji
Publication year - 2012
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jc007514
Subject(s) - froude number , turbulence , richardson number , buoyancy , mechanics , stratification (seeds) , turbulence kinetic energy , physics , stratified flow , shear (geology) , shear flow , meteorology , atmospheric sciences , thermodynamics , geology , flow (mathematics) , petrology , seed dormancy , germination , botany , dormancy , biology
This study proposes new parameterizations of diapycnal mixing by reanalyzing the results of previous laboratory and numerical experiments on homogeneous stably stratified shear flows. Unlike previous studies that use either the turbulent Froude number Fr or gradient Richardson number Ri g , this study parameterizes nondimensional momentum and buoyancy fluxes as functions of Fr and a turbulent shear number Sh, in order to quantify individual effects of shear and stratification. Turbulent momentum flux is found to depend linearly on Sh and to decrease monotonically with decreasing Fr. Turbulent buoyancy flux has a peak at moderate Fr. With increasing Sh, it decreases and increases at high and low Fr, respectively. The increase of Sh also cause relatively small but significant decreases of nondimensional turbulent properties, such as the nondimensional conversion rate of turbulent potential energy to background potential energy. The proposed parameterizations lie within the scatter of limited available field data. The parameterizations may be reduced to Ri g ‐based ones by incorporating the relationship between Ri g and turbulence intensity observed in the field. Existing stability functions for two‐equation turbulent closure schemes are found to over‐predict mixing efficiency at low Fr.