The along-wind diffusion of the tracer cloud in finite release experiments.

Abstract

The along-wind elongation of the tracer plume was observed in the medium-range atmospheric diffusion experiments with finite release time of air tracer substance. Since the elongated portion of a detached plume pursues the same course in the treatment of along-wind diffusion as an instantaneous puff, the along-wind diffusion parameter σx was estimated from the time variation of concentration in the elongated portion of the detached plume. This was compared with σx from other equivalent range experiments after grouping under stable, near neutral, and unstable classifications of atmospheric stability. In stable condition, a slight tendency to smaller σx values was recognized, but distinct dependency of σx growth on stability was not observed. Furthermore, consideration was taken of the valuation of time average concentration relating to the tracer release time, sampling time, and total time of tracer cloud passage. The method of evaluating the average concentration was considered, and it was made clear that the method was available for any sampling mode.