Abstract : A statistical analysis of smoke trail velocity profiles and balloon velocity profiles has been carried out to evaluate and remove their inherent noise content. The day-to-day variability in the probability of exceeding critical shear was evaluated. The corona anemometer data was compared with the much larger data-base of smoke trail data. Although the corona anemometer showed a higher probability of turbulence, it was within the variability expected from the smoke trail analysis. It is shown that the diffusion integral which leads to the diffusion coefficient is very sensitive to the variability in turbulent occurrence probabilities. (Author)