Plume Dispersion in the Convective Boundary Layer. Part II: Analyses of CONDORS Field Experiment Data

Abstract

Extensive analyses are performed on data from the CONDORS (convective diffusion observed with remote sensors) field experiment, described in detail by Ebeerhard et al. Convective scaling is used to facilitate comparisons with laboratory and numerical simulations and to give the results generality. Near-surface ?/Q from lidar-detected oil fog are generally in excellent agreement with nearby samples of coreleased SF6, considering the large spatial gradients found in the oil fog. Extrapolations to the surface of ??dy/Q of radar-detected ?chaff? agree reasonably well with most oil fog values after a mathematical compensation for the chaff's settling speed. Measured wind direction distributions compare favorably with ??dy and ??dz distributions of both tracers. The directly measured bulk variables σy, and σz, show little effect of source height or of tracer type except that surface-released σy are enhanced by up to 60% at X<0.3 [X =(x/U)w*/zi, where U is mean wind speed, w* is the convective scale velocity, and zi is mixing depth]. Generally, σy ≈ 0.6zi X = 0.6w*x/U at X < 1, σy ≈ 0.6ziX2/3 at X > 1, and σz ≈ 0.6ziX, until limited by reflections; σy systematically reduces for averaging times divided by zi/U less than 6. Also, for surface releases at small X, oil fog surface-extrapolated ??dy/Q gives good agreement with Nieuwstadt; with the Gaussian assumption, this implies σz ≈ 0.9ziX3/2. Composite patterns of Cy = Uzi??dy/Q versus X and z/zi for surface releases are substantially in agreement with Willis and Deardorff's laboratory and Lamb's LES simulations. In the aggregate, the oil and chaff measurements support a (1 + 2zs/zi) enhancement factor in maximum surface values of ??dy over Gaussian plume model predictions, with these maxima recurring mostly near x = 2zsU/w*, where zs, is source height. This agrees with most simulation results. Attention is focused on the effect of w? anomalies and persistence of Cy, patterns.