Simulation of tracer experiments using a numerical model for point sources in a sheared atmosphere

Abstract

In order to predict the distribution of material emanating from a point-source with adequate spatial resolution, the model was based on discrete solutions for serially-released puffs. The “across-wind” distribution of each puff was resolved into its zeroth, first and second moments in a moving frame of reference. Numerical solution for these moments accounted for spatially- and temporally-variant velocity and diffusivity profiles. It was found that the interaction of wind-shear and vertical diffusion spread material over a much larger area than is suggested by the popular Gaussian distribution, especially when a change in wind direction induces shear in a second dimension. Data collected in a series of detailed field experiments showed that the model provided significantly better predictions than an equivalent Gaussian Puff Model.