Evaluation of a new eddy diffusivity parameterisation from turbulent Eulerian spectra in different stability conditions

Abstract

A parameterisation for the vertical diffusivity has been recently derived by some of the authors. The formulation, based on the Taylor's statistical theory, the Hay and Pasquill working approximation concerning the relationship between Lagrangian and Eulerian turbulence spectra and a model for Eulerian spectra, relates plume dispersion in a boundary layer mainly to the turbulent eddies acting in the planetary boundary layer (PBL). The formulation represents in a realistic way both shear and buoyant turbulent mechanisms, which characterise the various regimes of the PBL and gives continuous values at any elevation and all stability conditions from unstable to stable. In this paper, the K-parameterisations, included in an advanced analytical model, have been tested and compared with a vertical dispersion scheme reported in literature, using experimental data in different emission conditions (low and tall stacks) and in several meteorological conditions ranging from stable to convective. Results show that (i) the dispersion model with the K-parameterisation included, produces a good fitting of the measured ground-level concentration data in all the experimental conditions considered; (ii) there are no big differences between the parameterisation proposed and the alternative taken from literature. The main advantage of the proposed model with respect to existing formulations consists mainly in its continuity at all elevations and for different stability regimes, resulting more physically correct.