Atmospheric Turbulence Structure at Three Vegetated Sites
Final rept. 1 Aug 1989-31 Jul 1991
CALIFORNIA UNIV DAVIS
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Atmospheric turbulence immediately above and within vegetation has features that distinguish it from that observed over smooth terrain. A variety of statistical properties demonstrate these differences, which are believed to be reflections of organized motions. The study involved the analysis of four data sets a deciduous forest, an almond orchard, a maize crop, and an English walnut orchard. Statistics included skewness, spectra, correlation coefficients, lagged correlations, and quadrant analysis. Overall, normalized statistics were remarkably similar for all four stands when vertically scaled by the height of the top of the vegetation, despite the large differences in the dimensions and vegetative structures of the stands. Objective schemes were used to detect ramp patterns in data from each site. Applied to the forest data, the multilevel scheme showed that a consistent number of ramps was detected in the humidity traces during each run, despite the fact that thermal stability changed during the observation period. Comparing the four canopies, the frequency of occurrence of ramps increased as stand height decreased. A consistent relationship was found when the frequency was plotted against a measure of the wind shear. It is demonstrated that the wavelet technique accurately detects scalar ramps.