Turbulence parameterisation for PBL dispersion models in all stability conditions

Accounting for the current knowledge of the planetary boundary layer (PBL) structure and characteristics, a new set of turbulence parameterisations to be used in atmospheric dispersion models has been derived, That is, expres sions for the vertical profiles of the Lagrangian length scale l(i) and tim e scale T-i and diffusion coefficient K-i, i = u, v, w, are proposed. The c lassical statistical diffusion theory, the observed spectral properties and observed characteristics of energy containing eddies are used to estimate these parameters. The results of this new method are shown to agree with pr eviously determined parameterisations. In addition, these parameterisations give continuous values for the PBL at all elevations(z(0) less than or equ al to z less than or equal to h, z(i)) and all stability conditions from un stable to stable, where h and z(i) are the turbulent heights in stable or n eutral and convective PBL, respectively, and L is the Monin-Obukhov length. It is the aim of this work to present the general derivations of these exp ressions and to show how they compare to previous results. Finally, a valid ation of the present parameterisation applied in a Lagrangian particle mode l, will be shown. The Copenhagen data set is simulated. This data set is pa rticularly suited for this validation, since most of the Copenhagen tracer experiments were performed in stability conditions that are the result of t he relative combination of wind shear and buoyancy forces. As a consequence , a parameterisation scheme, able to deal contemporary with neutral and sli ghtly convective condition, is to be preferred. (C) 2000 Elsevier Science L td. All rights reserved.