AN E-EPSILON-L TURBULENCE CLOSURE SCHEME FOR PLANETARY BOUNDARY-LAYERMODELS - THE NEUTRALLY STRATIFIED CASE

The standard E - epsilon model generates a planetary boundary layer th at appears to be much too deep. The cause of the problem is traced to the equation for the dissipation rate (epsilon) of turbulent kinetic e nergy (E), specifically the parameterization of dissipation production and destruction. In the context of atmospheric boundary-layer modelli ng, we argue that a part of the dissipation production should be model led as the input to the spectral cascade from the energy-containing pa rt of the spectrum, with a characteristic length l(epsilon), while the 'equilibrium' imbalance between local production and destruction of d issipation is modelled as proportional to E-2/E, as in the standard mo del. We propose an E - epsilon - l turbulence closure scheme, in which both the mixing length, l(m), and l(epsilon) are prescribed. The impo rtance of the a equation is diminished, though it still determines the dissipation rate in the E equation.