EDDY DIFFUSIVITIES FOR SENSIBLE HEAT, OZONE, AND MOMENTUM FROM EDDY-CORRELATION AND GRADIENT MEASUREMENTS

The eddy-correlation measurement technique was used to obtain micrometeorological field measurements of the fluxes of-momentum, sensible heat, and ozone at 3 and 8 meters at the Pawnee site. A method to accurately measure mass' (ozone) gradients from surface-layer-based meteorological towers was developed and used. Both flux and gradient: measurements were used for the determination of eddy diffusivities. Ozone was,Used as the mass tracer to explore similar relationships between the eddy diffusivities of momentum K-m Sensible heat K-h, and mass K-c. Eddy-diffusivity ratios were computed using dimensionless-gradient ratios classified from the data and regression models. These. ratios were classified by atmospherics stability determined at the geometric mean of the measurement heights. The assumption of similarity between the eddy diffusivities of ozone and sensible heat; K-c = K-h, based on scalar turbulent transfer theory, was verified for unstable atmospheric conditions. Eddy diffusivities of sensible heat are, however, 50% greater than diffusivities of ozone for stable atmospheric conditions. Chemical reaction of ozone, and/or the need for flux-measurement corrections, decrease the resulting values for ozone diffusivities during stable periods. Established eddy-diffusivity ratios for water vapor and momentum are valid for ozone and momentum under stable atmospheric conditions-over smooth terrain, but not-under unstable conditions for flow disturbed by irregular terrain. The relationships between the eddy diffusivities of momentum and ozone, as well as those between momentum and sensible heat, are controlled by free-convection conditions, K-m < K-c and K-m < K-h; these results are:inconclusive for unstable-atmospheric, smooth-terrain conditions for the Pawnee site during easterly winds. For disturbed-flow conditions at the Pawnee Site during westerly winds, the eddy diffusivities for momentum were enhanced and both K-c/K-m and K-h/K-m become approximately constant (0.35 and 0.5, respectively) for both stable and unstable conditions; Theoretical flux measurement corrections were applied to a subset of the data in an attempt to investigate the concept of a constant flux layer and to validate flux correction theory. The results indicate that. flux corrections are warranted. However, improvements to flux correction theory are needed; especially for stable atmospheric conditions, as demonstrated by the significant increase in data variability as a result of these corrections. The ''constant flux-layer'' concept holds for momentum flux and sensible heat flux, but is questionable for ozone flux.