Kinematic structure of a wildland fire plume observed by Doppler lidar

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 À1 . Divergence calculations made from the lidar radial velocities showed that the magnitude of convergence ranged between À0.06 and À0.08 s À1 downwind of the plumes, while a maximum of À0.14 s À1 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 À1 . Plume heights determined from sequential range height indicator scans provided estimates of vertical velocity between 0.4 and 0.6 m s

Environmental controls on pyrocumulus and pyrocumulonimbus initiation and development

“…The edge detection al- gorithm uses a combination of the lidar signal-to-noise ratio (SNR) and attenuated backscatter coefficient to isolate the plume. Similar approaches are presented in previous studies (Kovalelv et al, 2005;Charland and Clements, 2013). In our analysis, we first apply a 5th order Butterworth filter with a 5-point window to the SNR data along each lidar beam to eliminate some of the instrument noise.…”

“…Due to these sensitivities numerous previous studies have used lidars to examine smoke layers and smoke plumes (Banta et al, 1992;Kovalev et al, 2005;Pahlow et al, 2005;Charland and Clements, 2013;Lareau and Clements, 2015).…”

Evaluation of wildland fire smoke plume dynamics and aerosol load using UV scanning lidar and fire–atmosphere modelling during the Mediterranean Letia 2010 experiment

“…Lidar observations indirectly provide a measure of smoke density distribution. The usefulness of ground-based scanning lidars to assess plume rise dynamics and height was illustrated recently by Kovalev et al (2009), Wold et al (2010 and Charland and Clements (2013). Utkin et al (2003), Lavrov et al (2006) and Fernandes et al (2006) demonstrated the feasibility of forest-fire smoke detection using lidar even if the source is out of sight or under unfavourable visibility conditions.…”

The Fire and Smoke Model Evaluation Experiment—A Plan for Integrated, Large Fire–Atmosphere Field Campaigns

“…Key meteorological variables to characterize fire weather conditions and surface meteorology will include ambient air temperature, humidity, near-surface wind speed and direction of ambient and fire-induce wind fields [39]. Plume rise, entrainment, and fire-atmospheric circulations associated with the plume will be measured using in situ towers (e.g., [40]) and ground-based scanning Doppler LiDAR systems (ground and/or aircraft) [40][41][42], and a scanning Doppler dual-polarized, Ka-band radar system. Radars with dual-polarization capability have been shown to be useful for observing smoke plume structures and plume microphysics [43].…”