Sensitivities of the Atmospheric Response to a Wildland Fire using a Cloud-Resolving Model

Wildland fire behavior can be very difficult to predict because of inherent non-linearities and multi-scale processes associated with fire-atmosphere interactions. Circulations and complex flows in the vicinity of a fire are primarily driven by heat and moisture release from the fire. Since extreme conditions in the fire environment make collecting meteorological observations difficult, we employ a high-resolution numerical model to simulate the atmospheric responses to a fire. For this project we have chosen Cloud Model 1 (CM1) because it is designed to simulate high resolution, cloud scale processes. A surface sensible heat flux is added to CM1 to parameterize the effect of a fire and the resultant fire-induced circulations and complex flows are examined. Using CM1 allows us to produce simulations with fine spatial and temporal resolution with a detailed representation of the evolution of the fire-atmosphere system.

For the purpose of this study, we focus on the impact of the surface sensible heat flux on flows directly adjacent to and above the parameterized fire. By focusing on these near-fire features, we address the potential for fire-induced perturbations and the associated convective features to feed back on the fire. In this presentation, we present a series of sensitivity simulations that assess the impact on fire-induced flows of variations in the shape of the parameterized fire and of variations in background wind profiles. Fire shape and background wind variations are shown to influence the circulations and complex flows, and by doing so affect the plume characteristics in the proximity of the fire. These simulations, when combined with field studies and observations, help diagnose and refine our understanding of fire-atmosphere interactions. The results from this study can potentially help fire managers with ground-based decision making when fighting fires.