4.5 Observed Atmospheric Turbulence Regimes During Wildland Fires in Forested Environments

Tuesday, 5 May 2015: 4:15 PM
Great Lakes Ballroom (Crowne Plaza Minneapolis Northstar)
Warren E. Heilman, USDA Forest Service, Lansing, MI; and K. L. Clark, N. S. Skowronski, D. Seto, C. B. Clements, and X. Bian

Atmospheric circulations in the vicinity of wildland fires are inherently turbulent. These circulations, a manifestation of surface-vegetation-atmosphere and fire-atmosphere interactions, can influence fire behavior and the local dispersion of fire emissions. Recent measurements of the evolution of atmospheric turbulence regimes during wildland fires in forested environments are now providing new insight into how fires and forest overstory vegetation concurrently affect turbulent circulations that, in turn, influence fire spread, convective heat fluxes, and the directional mixing of smoke plumes. In this study, high frequency (10-Hz) in situ thermocouple temperature and sonic anemometer wind measurements carried out during prescribed backing and head fires in the New Jersey Pinelands National Reserve are analyzed to assess the effects of fire intensity and forest overstory vegetation on turbulent kinetic energy variability, turbulence anisotropy, the spectral characteristics of the three-dimensional turbulent wind fields, and horizontal and vertical turbulent heat fluxes. Key results from the analyses suggest that maximum fire-induced turbulence during surface fires may occur in an atmospheric layer above the forest canopy instead of near the surface, forest overstory vegetation affects the vertical variation in turbulence anisotropy, and the horizontal component of the total turbulent kinetic energy dominates the vertical component primarily at large turbulent eddy sizes.
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