Interpretation of Measured Tracer Concentration Fluctuations Using a Sinusoidal Meandering Plume Model

Abstract

Simultaneous instantaneous concentration and wind velocity fluctuations were measured 100 to 752 m downwind of a point source release of SF6 tracer during two field studies conducted amid rolling wheat fields and at a flat desert site in eastern Washington. Data from stable, neutron, and unstable conditions are interpreted using a meandering plume model where the meander is defined to be sinusoidal and the instantaneous plume profile is Gaussian. A sensitivity analysis of the model shows that the characteristic concentration time scale is a direct function of the meander time scale and the receptor position relative to the meander centerline. For narrow instantaneous plumes relative to the meander amplitude, the predicted mean crosswind profiles of concentration, intermittency factor, concentration fluctuation intensity, and peak-to-mean ratios exhibit bimodal distributions. Conditional (nonzero) concentration fluctuation intensifies calculated from the model are scattered about 1.0;, the scatter is the result of receptor location, meander amplitude, period, and instantaneous plume width. The magnitude of the scatter from model runs covering different receptor locations is essentially equal to the magnitude of the matter from the tracer observations. The simple meandering plume model thus provides a straightforward explanation of very complex patterns observed in the tracer concentration fluctuation data in terms of wind meander, receptor location, and instantaneous plume width.