Analysis of Fire-atmosphere Coupling Based on FireFlux 2 Experimental Data and WRF-SFIRE Simulations

Wildland fire behavior prediction is of key importance for community and firefighter safety. The ability to forecast the fire behavior under changing weather conditions has a potential to help in planning the fire suppression activities as well as evacuations. Unfortunately, realistic simulations of fire progression are very difficult due to the wide range of scales affecting the fire behavior, ranging from thousands of kilometers (synoptic systems affecting weather) to millimeters (the near-flame mixing affecting combustion). Additionally, the fire itself changes local meteorological conditions that in turn affect fire behavior. While numerical studies using coupled fire-atmosphere models have shed light on the dynamics of fire atmosphere-interactions, especially on the small scale, only recently have in-situ observational data become available to examine the fire-atmosphere coupling processes at scales closer to typical wildland fires. In this study we take advantage of the recent observational data collected during the FireFlux2 experiment to investigate the impact of the fire on the local meteorological conditions and fire-atmosphere coupling at the fire line. We analyze the in situ 3D sonic velocity data documenting the fire progression, in conjunction with simulations performed using WRF-SFIRE, to better understand the fire's impact on temperature and winds near the fire line, and to validate the model's performance. Both the measurements and the simulation indicate significant warming in the near surface (up to 250C), strong updrafts reaching 6 m/s, and significant near-surface flow at the fire line at reaching 6 m/s. A comparison between the simulations performed with and without coupling (no fire heat and moisture fluxes released to the atmosphere) suggests that the near surface acceleration induced by the fire significantly increases its progression speed. That suggests that the ability of coupled fire-atmosphere models to realistically render the wind field near the fire is extremely important for accurate simulation of fire progression.