Design of a nonsingular level 2.5 second-order closure model for the prediction of atmospheric turbulence

Abstract

The behavior of the Mellor and Yamada Level 2.5 second-order turbulence closure model is analysed over its entire domain of definition on the Ri × q2/qe2 plane, where Ri is the Richardson number of the mean flow and where q2/qe2 is the ratio of the turbulent kinetic energy predicted by the model to that which would obtain in a state of local equilibrium. The Level 2.5 model is reasonably accurate over the subdomain q2/qe2 ≥ 1, but it becomes unrealistic and pathological for the case of decaying turbulence (q2/qe2 < 1). The model is modified to take into account the effects of the growth rate, advection and vertical turbulent diffusion terms in the balance equations for all of the second moments, as well as the effects of the rapid return-to-isotropy or scrambling terms in the equations for the anisotropic components of the moments. The modified Level 2.5 model is proposed as a viable candidate for the prediction of turbulence and the simulation of the planetary boundary layer in general circulation models. -from Authors