No doublediffusion, shear only. The heat, momentum, and μ mixing efficiencies, as defined in Eq. (1f), vs. Ri for different values of the combination RePr which in the figures is denoted by Re_χ. In Fig. 1d we plot the turbulent Prandtl number σ_t defined in Eq. (14) vs. Ri for different Re_χ. In Fig. 1e we plot the Peclet number vs. Ri. In Fig. 1f we plot the data corresponding to the case Pe ≫ 1, which well reproduced well by the present model, lower curve in panel 1e. The data are as follows: meteorological observations (Kondo et al. 1978, slanting black triangles; Bertin et al. 1997, snow flakes), lab experiments (Strang & Fernando 2001, black circles; Rehmann & Koseff 2004, slanting crosses; Ohya 2001, diamonds), LES (Zilitinkevich et al. 2007a,b, triangles), DNS (Stretch et al. 2001, five-pointed stars).