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Kinematic structure of a wildland fire plume observed by Doppler lidar

Authors

  • A. M. Charland,

    1. Department of Meteorology and Climate Science, San José State University, San José, California, USA
    2. Now at Dept. of Atmospheric Sciences, University of Utah, Salt Lake City, Utah, USA
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  • C. B. Clements

    Corresponding author
    1. Department of Meteorology and Climate Science, San José State University, San José, California, USA
    • Corresponding author: C. B. Clements, Department of Meteorology and Climate Science, San José State University, San José, CA 95192, USA. (Craig.Clements@sjsu.edu)

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Abstract

[1] Wildland fires present a challenging environment to make meteorological measurements. Observations in the vicinity of wildland fires are needed to better understand fire-atmosphere interactions and to provide data for the evaluation of coupled fire-atmosphere models. An observational study was conducted during a low-intensity prescribed fire in an area of complex terrain with grass fuels east of San José, California. A ground-based scanning Doppler lidar acquired radial wind velocities and backscatter intensity in and around the fire plume from multiple horizontal and vertical scans. The development of a convergence zone was consistently observed to exist downwind of the plume and was indicated by a decrease in radial velocity of 3–5 m s−1. Divergence calculations made from the lidar radial velocities showed that the magnitude of convergence ranged between −0.06 and −0.08 s−1 downwind of the plumes, while a maximum of −0.14 s−1 occurred within the plume near the fire front. Increased radial velocities were observed at the plume boundary, indicating fire-induced acceleration of the wind into the base of the convection column above the fire front. Thermodynamic measurements made with radiosondes showed the smoke plume had a potential temperature perturbation of 3.0 to 4.4 K and an increase in water vapor mixing ratio of 0.5 to 1.0 g kg−1. Plume heights determined from sequential range height indicator scans provided estimates of vertical velocity between 0.4 and 0.6 m s−1, representing the ambient background vertical velocity as the top of the plume likely reached equilibrium.

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