Observations and Analysis of Fire-Atmosphere Interactions during Fire Front Passage

Wildfire responds to variations in fuels, topography, and weather. Wildfire frequency is expected to increase due to climate change, and fire management will become more important in the future. While numerical models are essential for predicting fire behavior and better simulations will improve fire fighter and public safety, there is a lack of observational data available for calibrating the model performances. Four experimental studies were conducted with various types of vegetation fuel and terrain using in-situ instrumented towers to better understand fire-atmosphere interactions at both large and fine scales. The first part of the thesis focuses on a unique observation of fire whirl formation during a valley wind-sea breeze reversal. We hypothesized that the fire whirl was caused by the interaction of the vertical wind shear with the fire front, which resulted in vorticity estimate of 0.2 s-1and turbulence kinetic energy of 10.4 m2s-2. In the second part, turbulence generated by fire was investigated using spectral analysis to determine the role fire had on the energy spectrum of the wind and temperature. The results showed increased energy in velocity and temperature spectra at high frequency during fire front passage (FFP) for all four cases, but the spectral energy of velocity components at lower frequencies may be affected by cross-flow intensity, topography, presence of canopy layer, and degree of fire-atmosphere coupling. The velocity spectra observed during FFP collapsed into a narrow band at high frequency. The observed temperature spectra did not converge into a narrow range