The Experts below are selected from a list of 54669 Experts worldwide ranked by ideXlab platform
S S Zilitinkevich - One of the best experts on this subject based on the ideXlab platform.
-
Similarity Theory and calculation of turbulent fluxes at the surface for the stably stratified atmospheric boundary layer
Boundary-Layer Meteorology, 2007Co-Authors: S S Zilitinkevich, Igor EsauAbstract:In this paper we revise the Similarity Theory for the stably stratified atmospheric boundary layer (ABL), formulate analytical approximations for the wind velocity and potential temperature profiles over the entire ABL, validate them against large-eddy simulation and observational data, and develop an improved surface flux calculation technique for use in operational models.
-
an extended Similarity Theory for the stably stratified atmospheric surface layer
Quarterly Journal of the Royal Meteorological Society, 2000Co-Authors: S S Zilitinkevich, Pierluigi CalancaAbstract:An advanced Similarity-Theory formulation for the wind and temperature profiles in the stably stratified atmospheric surface layer (ASL) is developed with due regard to the effect of the free-flow static stability on the ASL. In the revised log-linear profiles, empirical coefficients traditionally considered as universal constants, namely the slope factors in the z-less stratification layer (beyond the logarithmic sub-layer), become functions of the dimensionless number S = N L/u * . Here, N is the Brunt-Vaisala frequency in the free flow, L is the Monin-Obukhov length, and u * is the friction velocity. The number S indicates how strongly the ASL is affected by the free-flow stability. This new formulation leaves room for the occurrence of well developed turbulence at much higher Richardson numbers, Ri, than had been suspected. Moreover, it results in a pronounced dependence of the turbulent Prandtl number on Ri in a wide range of Ri, including the z-less stratification layer, in correspondence with long-standing empirical evidence. The traditional Monin-Obukhov Similarity Theory disregards the above essential features of the stably stratified ASL. New data from measurements over a slightly inclined plateau in West Greenland provide experimental support for the proposed Theory.
Ola P G Persson - One of the best experts on this subject based on the ideXlab platform.
-
Similarity Theory based on the dougherty ozmidov length scale
Quarterly Journal of the Royal Meteorological Society, 2015Co-Authors: Peter S. Guest, Alexey A Grachev, Christopher W. Fairall, Edgar L. Andreas, Ola P G PerssonAbstract:This article describes a local Similarity Theory for developed turbulence in the stably stratified boundary layer that is based on the Brunt–Vaisala frequency and the dissipation rate of turbulent kinetic energy instead of the turbulent fluxes used in the traditional Monin–Obukhov Similarity Theory. Based on dimensional analysis (Pi theorem), it is shown that any properly scaled statistics of the small-scale turbulence are universal functions of a stability parameter defined as the ratio of a reference height z and the Dougherty–Ozmidov length scale, which in the limit of z-less stratification is linearly proportional to the Obukhov length scale. Measurements of atmospheric turbulence made at five levels on a 20 m tower over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to examine the behaviour of different Similarity functions in the stable boundary layer. In the framework of this approach the non-dimensional turbulent viscosity is equal to the gradient Richardson number, whereas the non-dimensional turbulent thermal diffusivity is equal to the flux Richardson number. These results are a consequence of the approximate local balance between production of turbulence by shear in the mean flow and viscous dissipation. The turbulence framework based on the Brunt–Vaisala frequency and the dissipation rate of turbulent kinetic energy may have practical advantages for estimating turbulence when the fluxes are not directly available.
-
the critical richardson number and limits of applicability of local Similarity Theory in the stable boundary layer
Boundary-Layer Meteorology, 2013Co-Authors: Andrey A Grachev, Peter S. Guest, Christopher W. Fairall, Edgar L. Andreas, Ola P G PerssonAbstract:Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to determine the limits of applicability of Monin–Obukhov Similarity Theory (in the local scaling formulation) in the stable atmospheric boundary layer. Based on the spectral analysis of wind velocity and air temperature fluctuations, it is shown that, when both the gradient Richardson number, Ri, and the flux Richardson number, Rf, exceed a ‘critical value’ of about 0.20–0.25, the inertial subrange associated with the Richardson–Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in this supercritical regime, but this is non-Kolmogorov turbulence, and it decays rapidly with further increasing stability. Similarity Theory is based on the turbulent fluxes in the high-frequency part of the spectra that are associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band diminish as the Richardson–Kolmogorov energy cascade weakens; therefore, the applicability of local Monin–Obukhov Similarity Theory in stable conditions is limited by the inequalities Ri < Ri cr and Rf < Rf cr. However, it is found that Rf cr = 0.20–0.25 is a primary threshold for applicability. Applying this prerequisite shows that the data follow classical Monin–Obukhov local z-less predictions after the irrelevant cases (turbulence without the Richardson–Kolmogorov cascade) have been filtered out.
Pierluigi Calanca - One of the best experts on this subject based on the ideXlab platform.
-
an extended Similarity Theory for the stably stratified atmospheric surface layer
Quarterly Journal of the Royal Meteorological Society, 2000Co-Authors: S S Zilitinkevich, Pierluigi CalancaAbstract:An advanced Similarity-Theory formulation for the wind and temperature profiles in the stably stratified atmospheric surface layer (ASL) is developed with due regard to the effect of the free-flow static stability on the ASL. In the revised log-linear profiles, empirical coefficients traditionally considered as universal constants, namely the slope factors in the z-less stratification layer (beyond the logarithmic sub-layer), become functions of the dimensionless number S = N L/u * . Here, N is the Brunt-Vaisala frequency in the free flow, L is the Monin-Obukhov length, and u * is the friction velocity. The number S indicates how strongly the ASL is affected by the free-flow stability. This new formulation leaves room for the occurrence of well developed turbulence at much higher Richardson numbers, Ri, than had been suspected. Moreover, it results in a pronounced dependence of the turbulent Prandtl number on Ri in a wide range of Ri, including the z-less stratification layer, in correspondence with long-standing empirical evidence. The traditional Monin-Obukhov Similarity Theory disregards the above essential features of the stably stratified ASL. New data from measurements over a slightly inclined plateau in West Greenland provide experimental support for the proposed Theory.
Alexey A Grachev - One of the best experts on this subject based on the ideXlab platform.
-
Similarity Theory based on the dougherty ozmidov length scale
Quarterly Journal of the Royal Meteorological Society, 2015Co-Authors: Peter S. Guest, Alexey A Grachev, Christopher W. Fairall, Edgar L. Andreas, Ola P G PerssonAbstract:This article describes a local Similarity Theory for developed turbulence in the stably stratified boundary layer that is based on the Brunt–Vaisala frequency and the dissipation rate of turbulent kinetic energy instead of the turbulent fluxes used in the traditional Monin–Obukhov Similarity Theory. Based on dimensional analysis (Pi theorem), it is shown that any properly scaled statistics of the small-scale turbulence are universal functions of a stability parameter defined as the ratio of a reference height z and the Dougherty–Ozmidov length scale, which in the limit of z-less stratification is linearly proportional to the Obukhov length scale. Measurements of atmospheric turbulence made at five levels on a 20 m tower over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to examine the behaviour of different Similarity functions in the stable boundary layer. In the framework of this approach the non-dimensional turbulent viscosity is equal to the gradient Richardson number, whereas the non-dimensional turbulent thermal diffusivity is equal to the flux Richardson number. These results are a consequence of the approximate local balance between production of turbulence by shear in the mean flow and viscous dissipation. The turbulence framework based on the Brunt–Vaisala frequency and the dissipation rate of turbulent kinetic energy may have practical advantages for estimating turbulence when the fluxes are not directly available.
-
Similarity Theory based on the Dougherty-Ozmidov length scale
arXiv: Atmospheric and Oceanic Physics, 2014Co-Authors: Alexey A Grachev, Peter S. Guest, Christopher W. Fairall, Edgar L. Andreas, P. Ola G. PerssonAbstract:Local Similarity Theory is suggested based on the Brunt-Vaisala frequency and the dissipation rate of turbulent kinetic energy instead the turbulent fluxes used in the traditional Monin-Obukhov Similarity Theory. Based on dimensional analysis (Pi theorem), it is shown that any properly scaled statistics of the small-scale turbulence are universal functions of a stability parameter defined as the ratio of a reference height z and the Dougherty-Ozmidov length scale which in the limit of z-less stratification is linearly proportional to the Obukhov length scale. Measurements of atmospheric turbulence made at five levels on a 20-m tower over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to examine the behaviour of different Similarity functions in the stable boundary layer. It is found that in the framework of this approach the non-dimensional turbulent viscosity is equal to the gradient Richardson number whereas the non-dimensional turbulent thermal diffusivity is equal to the flux Richardson number. These results are a consequence of the approximate local balance between production of turbulence by the mean flow shear and viscous dissipation. The turbulence framework based on the Brunt-Vaisala frequency and the dissipation rate of turbulent kinetic energy may have practical advantages for estimating turbulence when the fluxes are not directly available.
-
The Critical Richardson Number and Limits of Applicability of Local Similarity Theory in the Stable Boundary Layer
Boundary-Layer Meteorology, 2013Co-Authors: Alexey A Grachev, Peter S. Guest, Christopher W. Fairall, Edgar L. Andreas, P. Ola G. PerssonAbstract:Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to determine the limits of applicability of Monin–Obukhov Similarity Theory (in the local scaling formulation) in the stable atmospheric boundary layer. Based on the spectral analysis of wind velocity and air temperature fluctuations, it is shown that, when both the gradient Richardson number, Ri , and the flux Richardson number, Rf , exceed a ‘critical value’ of about 0.20–0.25, the inertial subrange associated with the Richardson–Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in this supercritical regime, but this is non-Kolmogorov turbulence, and it decays rapidly with further increasing stability. Similarity Theory is based on the turbulent fluxes in the high-frequency part of the spectra that are associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band diminish as the Richardson–Kolmogorov energy cascade weakens; therefore, the applicability of local Monin–Obukhov Similarity Theory in stable conditions is limited by the inequalities Ri
Igor Esau - One of the best experts on this subject based on the ideXlab platform.
-
Similarity Theory and calculation of turbulent fluxes at the surface for the stably stratified atmospheric boundary layer
Boundary-Layer Meteorology, 2007Co-Authors: S S Zilitinkevich, Igor EsauAbstract:In this paper we revise the Similarity Theory for the stably stratified atmospheric boundary layer (ABL), formulate analytical approximations for the wind velocity and potential temperature profiles over the entire ABL, validate them against large-eddy simulation and observational data, and develop an improved surface flux calculation technique for use in operational models.
