Efficiency of eddy mixing in a stable stratified atmospheric boundary layer

Based on a mesoscale RANS model of turbulence, the behavior of turbulent eddy mixing parameters is found to agree with the latest data of laboratory and atmospheric measurements. Some problems of the description of turbulent eddy mixing in the atmospheric boundary layer are studied. When the flow transforms to an extremely stable state, in particular, it is found the flux Richardson number Ri$_f$ can change nonmonotonically: it increases with increasing gradient Richardson number Ri$_g$ until the state of saturation is reached at Ri$_g\simeq$ 1 and then decreases. The behavior of the coefficients of eddy diffusion of momentum and heat agrees with the concept of momentum (but not heat) transfer by internal waves propagating in an extremely stable atmospheric boundary layer.