Effect of Vertical Wind Shear on the Grassfire Evolution

Based on available observational data, Byram suggested that low-level jets or ambient wind profiles with wind speed decreasing with height favor extremely erratic wildfire behavior. The UULES-wildfire coupled model is used to examine, in a controlled and systematic way, how several wind profiles in Byram's most dangerous wind profile category affect grass fire evolution. Through comparative numerical simulations, we hope to address such questions as how the kinetic energy converted from fire-released energy in the fire-induced convective column is transported to the surface from aloft to drive fires to ever-increasing intensities. We also examine effect of turbulence in the boundary layer on this transport of the kinetic energy. One important variable to examine is vorticity. Intense vorticity has been observed in wildfires and does play an important role in the evolution of the extreme wildfire behavior such as the development of fire whirls in and ahead of the fire front.