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Diffusion in the Surface Layer of the Convective Boundary Layer

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Final rept. 14 Mar 1988-30 Apr 1990

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Dispersion in the planetary boundary layer PBL is important in a variety problems including air pollution and obscurant cloud behavior in a battlefield environment. Dispersion is a stochastic phenomena caused by the random or stochastic nature of PBL turbulence, and the fluctuating concentration field often is as important as the mean field. Indeed, laboratory measurements show that the root-mean-square rms fluctuating concentration, sigma sub c, in plumes from continuous point sources can be 5 times greater than the ensemble-mean concentration C a similar situation exists in smoke clouds. Thus, sigma sub c, as well as C must be estimated to assess the visibility limits of an obscurant cloud or the air quality effects of a pollution source. Under this program, stochastic dispersion models have been developed for the C and sigma sub c fields due to a passive tracer source in the convective boundary layer CBL, with the main aim of improving the understanding and predictability of dispersion in that layer. Effects were focused on the CBL because 1 the PBL is in a convective state a substantial fraction of the time equivalent 30 - 40, 2 the turbulence structure of the CBL is well documented, and 3 laboratory data and numerical results exist for testing models. Furthermore, dispersion in the CBL cannot be modeled by the standard statistical or eddy-diffusion theories because of the complications caused by the CBL turbulence-its vertical inhomogeneity, vertical velocity skewness, and large time scale.

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  • Inorganic Chemistry

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