Role of horizontal eddy diffusivity within the canopy on fire spread

Wind profile observations are used to estimate turbulent properties in the atmospheric boundary layer from 1 m up to 300 m height above north Florida pine woods. Basic turbulence characteristics of the lower boundary layer are presented. Together with theoretical models for the mean horizontal velocity we derive the lateral diffusivity using Taylor's frozen turbulence hypothesis in the surface fuel layer (tens of centimeters). This parameter is used to predict the spread of surface fires in a simple 1D model. Initial assessments of sensitivity of the fire spread rates to the lateral diffusivity are made. Estimated lateral diffusivity with and without fire are made and associated fire spread rates are explored. Our results support the conceptual framework that eddy dynamics in the fuel layer is set by larger eddies developed in the canopy layer aloft. The presence of fire modifies the eddy structure depending on the fire intensity.