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Diapycnal diffusivities in homogeneous stratified turbulence
Author(s) -
Stretch D. D.,
Venayagamoorthy S. K.
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl041514
Subject(s) - turbulence , thermal diffusivity , scaling , k epsilon turbulence model , dissipation , stratification (seeds) , scalar (mathematics) , stratified flows , homogeneous , physics , mechanics , mixing (physics) , turbulence kinetic energy , scale (ratio) , stratified flow , thermodynamics , geometry , mathematics , seed dormancy , germination , botany , quantum mechanics , dormancy , biology
Quantifying diapycnal mixing in stably stratified turbulence is fundamental to the understanding and modeling of geophysical flows. Data of diapycnal mixing from direct numerical simulations of homogeneous stratified turbulence and from grid turbulence experiments, are analyzed to investigate the scaling of the diapycnal diffusivity. In these homogeneous flows the instantaneous diapycnal diffusivity is given exactly by K d = ε ρ /(∂/∂ z ) 2 where ρ is the dissipation rate of density fluctuations, and ∂ is the mean density gradient. The diffusivity K d may be expressed in terms of the large scale properties of the turbulence as K d = γL E 2 / T L , where L E is the Ellison overturning length‐scale, T L is the turbulence decay time‐scale, and γ is half the mechanical to scalar time‐scale ratio. Our results show that L E and T L can explain most of the variations in K d over a wide range of shear and stratification strengths while γ remains approximately constant.