Simulations of Buoyancy-Generated Horizontal Roll Vortices over Multiple Heating Lines

Abstract

Abstract A two-dimensional nonhydrostatic atmospheric model is used to simulate the boundary-layer circulations that develop from multiple lines of extremely high surface temperatures. Numerical simulations are carried out to investigate the role of buoyancy and ambient crossflow effects in generating horizontal roll vortices in the vicinity of adjacent wildland fire perimeters. Numerical results suggest that the downdraft segments of buoyancy-generated horizontal roll vortices can be reinforced when multiple heating lines are present, with the degree of reinforcement dependent on the heating-line spacing. Significant low-level horizontal flow directly over the bounding heating lines is observed in some simulations, suggesting a mechanism for low-level flame migration in actual wildland fires. Multiple heating lines also affect the development and behavior of buoyancy-generated horizontal roll vortices when ambient crossflows are present. Simulations indicate that vortices are more likely to persist for multiple heating lines than for a single heating line when light ambient crossflows are introduced. Although simulation results should be viewed qualitatively, they suggest the potential importance of adjacent fire perimeters in actual wildland fire episodes for the development and behavior of buoyancy-generated horizontal roll vortices. For. Sci. 40(4):601-617.