A random walk model for dispersion in inhomogeneous turbulence in a convective boundary layer

摘要: It is necessary for a random walk model to satisfy the well-mixed criterion which requires that if particles of tracer are initially well mixed in ambient fluid they will remain so. Models applied so far dispersion convective boundary layer where turbulence inhomogeneous and skew require non-Gaussian forcing do not this condition. In work developed based on approach Thomson (1987, J. Fluid Mech.180,529–556) satisfies condition, incorporates skewness vertical velocity has Gaussian forcing. The skewed probability distribution function (PDF) equation Baerentsen Berkowicz (1984, Atmospheric Environment18, 701–712) used derive equation. diffusion layer. validity closure assumption σA = wAand σb wA, σB updraft downdraft standard deviations, respectively wA andwB mean velocities, respectively, analyzed quantitatively with measured values various statistical parameters involved PDF Results reveal quite satisfactory. new general reduces one-dimensional equations Wilson et al. (1983, Boundary-Layer Met. 27,163–169) Mech. 180, 529–556) when without any flow, basic Langevin homogeneous. Predictions made dimensionless crosswind integrated concentrations, particle height, spread three source heights step sizes. comparison results laboratory measurements Willis Deardorff(1976, Q. Jl R. met. Soc.102,427–445; 1978, Environment12,1305–1311; 1981, Environment15,109–117) de Baas (1986, Soc.112,165–180) Sawford Guest atmos. Sci.44,1152–1165) models forcing, shows simulates experimental features well. becomes homogeneous after X≈6. maximum ground level concentrations better predicted by model.