| Observations in the vicinity of a wildland fire showed the development of a convergence zone downwind of the convection column. These observations were obtained during a prescribed burn in complex terrain east of San Jose, California. A ground-based Halo Photonics, Ltd. Stream Line 75 Lidar acquired Doppler wind velocities and backscatter intensity in and around the fire plume from multiple vertically pointing, PPI, and RHI scans while a ASC miniSodar obtained vertical wind and turbulence profiles downwind. These observations allowed for the study of the kinematic structure and spatial and temporal evolution of the fire plume. Observations showed velocities accelerating at the plume boundary, indicating an inflow into the base of the convective updraft. The development of a convergence zone was observed by decreases in radial velocity of 3-5 m s-1 downwind of the plume compared to velocities near the fire front. This deceleration of the wind was also observed from sodar measurements downwind of the fire. An increase in potential temperature within the plume of 3.0-4.4 K was observed with an increase in mixing ratio of 0.5-1.0 g kg-1. Increased turbulent mixing was found within the plume with an increase in turbulent kinetic energy of 3 m2 s-2 within the plume and updraft velocities near 1 m s -1. In addition, methods were developed for estimating the fire spread rate and the rate of spread of the plume. |
