A Comparison of Turbulence Intensity and Stability Ratio Measurements to Pasquill Stability Classes

Abstract

To understand the extent to which the Pasquill stability classes can discriminate the diffusion capability of the atmosphere, a comparison between stability category and both turbulence intensity and stability ratio was performed. Data for stability class were gathered from observations taken at 3-hr intervals at the Augusta, Ga., weather station. Turbulence intensity and stability ratio data were recorded on a tower 13 km away. For each observation at Augusta, the stability category was determined, based on month, hour, cloud cover and character, height, and wind speed. The distribution was then formed from all of the quantitative data for each category. Results showed a monotonic decrease in median turbulence intensity by an order of magnitude as stability class went from A through F. However, the distribution within a class was characterized by a geometric standard deviation of about 3, indicating large scatter of individual values about the median. The median of the stability ratio distributions increased as stability changed from class A to F but, for classes D, E, and F, the trend was not well defined. In particular, it appears that category D is not a good predictor of a near adiabatic (neutral) lapse rate.