Modeling Wind Field and Pollution Transport over a Complex Terrain Using an Emergency Dose Information Code SPEEDI

Abstract

Atmospheric dispersion code system SPEEDI (System for Prediction of Environmental Emergency Dose Information) has been applied to simulate the field experiments conducted over a complex terrain. A diagnostic mass-consistent wind field model of the code system simulates the flow over an isolated hill using the routinely measured data from sodars and a meteorological tower. An objective basis for the adjustment of the horizontal and vertical wind components has been incorporated in the model, and the results show a great improvement in modeling the flow past the hill. Calculated profiles of the vertical velocity component around the hill have been compared with those observed by the sodars. The model streamlines show close agreement with the tetroon trajectory and the ground-level concentration patterns. Dispersion calculations are carried out using a Lagrangian particle random walk model. The dispersion algorithm is modified in order to utilize the observed turbulence data instead of the conventional Pasquill?Gifford method, and the former scheme performs better in simulating the concentration distribution. Results suggest that the accuracy of the code system improves significantly when all these changes are introduced.