Multifractal analysis of line-source plume concentration fluctuations in surface-layer flows

A codimension multifractal methodology was used to analyze and to model sca lar concentration fluctuations within sulfur hexafluoride tracer gas plumes from a line source in atmospheric surface-layer flows. Correspondence was exhibited between the double trace moments parameters a and C-1 of the codi mension methodology and the experimentally measured plume concentration cha racteristics of peak-to-mean ratio and concentration fluctuation intensity. Data series were generated using an extremal Levy, stochastic multifractal model, with the experimental a and C-1 as inputs. Uncertainties in experim entally determined plume characteristic values overlapped the uncertainties in model-simulated values. The utility of the procedure includes 1) charac terizing the state of scalar turbulent mixing, 2) helping to evaluate and t o model hazardous plume concentrations, and 3) being able to estimate the p robability of realizing extreme events at timescales of observation beyond or at magnitudes in excess of those present in the actual observations.