Numerical Analysis of Atmospheric Perturbations Induced by Large Wildfire Events

This study analyzes fire-induced winds from a wind-driven fire (Thomas Fire) and a plume-dominated fire (Creek Fire). Two numerical experiments, one without the fire present and the other with the fire, were used. The fire-induced perturbations were then estimated by subtracting a variable value in the “No Fire Run” from the “Fire Run” (Fire - No Fire). For this study, spatial and temporal variability of winds, geopotential height, and convergence were analyzed. Furthermore, cloud water mixing ratio, precipitation, and fuel moisture were analyzed during the Creek Fire to assess fire-induced rainfall and its impact on fuel moisture. It was found that the wind-driven Thomas Fire created more widespread and generally stronger fire-induced winds than the plume-dominated Creek Fire. In addition, fire-induced wind speeds during the Creek Fire followed a diurnal cycle, while the Thomas Fire showed much less temporal variability. When analyzing geopotential height, the results were very similar to other idealized simulations. A localized low-pressure region was observed in front of the fire front, with a preceding high-pressure area. When analyzing precipitation, it was found that the fire increased precipitation accumulation in the area surrounding the active fire. This created an increase in fuel moisture which could have helped locally decelerate the fire spread. Further research into the processes behind fire-atmosphere interactions will lead to a better understanding of fire behavior and the extent to which these interactions can impact the fire environment. These studies will help assess the limitations of uncoupled operational models and improve fire modeling overall.