Analysis of the Sensitivity of Mean and Turbulent Flow to a Simulated Low-Intensity Fire

We use the recently developed ARPS-CANOPY model to examine whether the degree of sensitivity of mean and turbulent flow in the roughness sub-layer to a low-intensity fire is dependent on canopy and background atmospheric properties. ARPS-CANOPY is a modified version of the Advanced Regional Prediction System (ARPS) model in which the effects of vegetation elements (e.g., branches, leaves) on drag, turbulence production/dissipation, radiation transfer, and the surface energy budget are accounted for through modifications to the ARPS model equations. Specific parameters examined in this study include canopy density, ambient surface/canopy heating, and background wind speed. Sensitivity experiments reveal that in all cases, downwind roughness layer turbulence increases with the presence of a surface fire, however, the atmospheric response is muted by the presence of vegetation. The impact of the fire on mean and turbulent flow is most pronounced in simulations where no heat source is applied other than the fire, and less pronounced in simulations where an additional heat source is prescribed to represent typical midday heating. Analysis of the effect of the fire on the degree of turbulence anisotropy in and above the canopy is also presented. We conclude the presentation with some discussion of the relevance of our findings to prediction of local smoke dispersion from low-intensity fires, and more specifically, how improved understanding of atmospheric model sensitivities can assist smoke managers in the interpretation of smoke prediction products.