A skewed homogeneous lagrangian particle model for convective conditions

Abstract Numerical solution of the Langevin equation for convective conditions usually requires quite small time steps in order to resolve properly the smaller-scale turbulence near the boundaries. This time step restriction can be eased significantly if it is assumed that the turbulence is uniform over the whole depth of the mixed layer. In this paper, we investigate the effect of this homogeneous turbulence assumption on ground-level concentration (glc) by comparing results with (a) the Willis and Deardorff laboratory experiments on dispersion in fully convective conditions and (b) the predictions of a model employing a more realistic inhomogeneous parameterization for the turbulence. As far as the ability to predict the magnitude and location of the near-source maximum glc, and the ability to maintain a well-mixed profile further downwind are concerned, we conclude that the assumption of homogeneous turbulence is quite adequate. We also compare Gaussian and skewed distributions for homogeneous turbulence and show that realistic results in convective conditions can only be obtained with the skewed distribution.

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