Eddy mixing of momentum and heat in stably stratified boundary layers: Numerical study

Abstract

Abstract The paper analyzes the features of turbulent momentum and heat transfer in a stably stratified atmospheric boundary layer (ABL), in the upper troposphere and lower stratosphere, and the possibility of taking them into account in RANS (Reynolds Average Navier Stokes) turbulence models. Such features, for example, include the transfer of momentum (but not heat) by internal gravitational waves under conditions of strong stability, the formation of a low-level jet. Models for the coefficients of eddy diffusion of momentum and heat were obtained by writing the differential equations for the Reynolds stresses and the turbulent heat flux vector in the weakly equilibrium approximation, in which the advection and diffusion of some dimensionless quantities are neglected. In the considered version of the algebraic model built on the physical principles of the RANS approximation for stratified turbulence, three prognostic equations are used: for the kinetic energy of turbulence, the rate of its spectral consumption and the dispersion of temperature fluctuations. It is shown that the profile of the vertical diffusivity for momentum, which was calculated using three-parametric turbulent model, is in agreement with data of direct measurements either within a stable stratified atmospheric boundary layer or beyond this layer in free atmosphere.