||Multi-Stream Model for Vertical Mixing of a Passive Tracer in the Convective Boundary Layer.
Han, J. ;
Byun, D. W. ;
||North Carolina State Univ. at Raleigh. Dept. of Marine, Earth and Atmospheric Sciences. ;National Oceanic and Atmospheric Administration, Research Triangle Park, NC. Atmospheric Sciences Modeling Div.;Environmental Protection Agency, Research Triangle Park, NC. National Exposure Research Lab.
Three-dimensional models ;
Convective flow ;
Boundary layer flow ;
Vertical air currents ;
Tracer techniques ;
Mixing height ;
Convection currents ;
Atmospheric turbulence ;
Ecological concentration ;
Environmental transport ;
Large eddy simulation ;
Probability density functions ;
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||We study a multi-stream model (MSM) for vertical mixing of a passive tracer in the convective boundary layer, in which the tracer is advected by many vertical streams with different probabilities and diffused by small scale turbulence. We test the MSM algorithm for investigating the effects of inhomogenous mixing and vertical transport of multiple pollutants at different source heights in a three-dimensional air quality model. All input parameters in the MSM such as the probability density function and the mean updraft and downdraft are prescribed from large-eddy simulation (LES) data and the mixed-layer similarity theory. Applicability of the MSM is tested against the LES results for both near surface and elevated tracer sources. Results from the MSM compare well with those from LES for the overall temporal behavior of concentration distributions. However, a somewhat poor agreement between the MSM and LES is seen in the magnitude of the concentrations at the surface and in the entrainment zone. It suggests that a further improvement of the MSM is needed to account for the frictional effects at the surface and the diffusion by small scale turbulence in the entrainment zone.
||Prepared in cooperation with National Oceanic and Atmospheric Administration, Research Triangle Park, NC. Atmospheric Sciences Modeling Div. Sponsored by Environmental Protection Agency, Research Triangle Park, NC. National Exposure Research Lab.
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||PC A02/MF A01