1.1
Statistical Variability of Dispersion in the Atmospheric Boundary Layer
Jeffrey C. Weil, CIRES/Univ. of Colorado, Boulder, CO; and P. P. Sullivan, C. H. Moeng, and E. G. Patton
Dispersion in the atmospheric boundary layer is a random process driven by the stochastic nature of turbulence. As a result, the statistically fluctuating concentration observed at some location downwind of a source is typically as large as the mean concentration. This statistical or stochastic variability in concentration is important in a number of problems such as estimating the peak concentration of toxic or hazardous materials, determining the threshold for odor detection, and evaluating dispersion models.
This paper presents computations of the stochastic variability in concentration from sources in the convective boundary layer (CBL) using a Lagrangian particle dispersion model driven by velocity fields from large-eddy simulations (LES). The LESs were conducted for a 5 km X 5 km X 2 km domain under conditions of strong convective mixing with weak winds--a mean wind speed of 3 m/s. A realization of the concentration field from a single sourcewas obtained by tracking about 70,000 particles in fine-time resolution using the resolved and subgrid-scale LES velocity fields. Thirty realizations of the concentration field for a given source height were found by computing the concentrations separately for 30 different source locations in the horizontal plane; the sources were separated by large distances to achieve statistical independence. The concentration fields were computed for a surface source and two elevated releases. The computed variability for the surface source was in good agreement with that found from two field experiments. The results are quite encouraging, and the approach can be appliedto other CBLs as well as the stable boundary layer.
.Session 1, Advanced Modeling of Dispersion and Air Quality on All Scales: Part I
Monday, 30 January 2006, 9:00 AM-12:00 PM, A407
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