Abstract
Abstract. Vegetation fires emit large amount of gases and aerosols which are detrimental to human health. Smoke exposure near and downwind of fires depends on the fire propagation, the atmospheric circulations and the burnt vegetation. A better knowledge of the interaction between wildfire and atmosphere is a primary requirement to investigate fire smoke and particle transport. The purpose of this paper is to highlight the usefulness of an UV scanning lidar to characterise the fire smoke plume and consequently validate fire–atmosphere model simulations. An instrumented burn was conducted in a Mediterranean area typical of ones frequently subject to wildfire with low dense shrubs. Using lidar measurements positioned near the experimental site, fire smoke plume was thoroughly characterised by its optical properties, edge and dynamics. These parameters were obtained by combining methods based on lidar inversion technique, wavelet edge detection and a backscatter barycentre technique. The smoke plume displacement was determined using a digital video camera coupled with the lidar. The simulation was performed using a mesoscale atmospheric model in a large eddy simulation configuration (Meso-NH) coupled to a fire propagation physical model (ForeFire), taking into account the effect of wind, slope and fuel properties. A passive numerical scalar tracer was injected in the model at fire location to mimic the smoke plume. The simulated fire smoke plume width remained within the edge smoke plume obtained from lidar measurements. The maximum smoke injection derived from lidar backscatter coefficients and the simulated passive tracer was around 200 m. The vertical position of the simulated plume barycentre was systematically below the barycentre derived from the lidar backscatter coefficients due to the oversimplified properties of the passive tracer compared to real aerosol particles. Simulated speed and horizontal location of the plume compared well with the observations derived from the videography and lidar method, suggesting that fire convection and advection were correctly taken into account.
Highlights
Southern Europe and the Mediterranean basin are regularly affected by forest fires which can burn thousands of hectares in a few days
An instrumented field experimental burn was performed in the mountainous Mediterranean region of Letia, Corsica, a typical great wildfire danger area
Aerosol optical properties and the fire smoke plume edge and main locations were derived from a combination of methods based on lidar inversion technique, wavelet edge detection method and a backscatter barycentre technique
Summary
Southern Europe and the Mediterranean basin are regularly affected by forest fires which can burn thousands of hectares in a few days. A recent publication from the European Forest Fire Information System accounts for 65 000 fires which occur in Europe every year, burning half a million hectares of vegetation and forest, with 85 % of the burnt area being in the European Mediterranean region (San-Miguel-Ayanz et al, 2012). Considerable efforts were made to characterize the organic and inorganic compounds in the gas and particulate phases from prescribed fires (Lee et al, 2005; Yan et al, 2008; Alves et al, 2011; Burling et al, 2011) or uncontrolled fires (Alves et al, 2010; Vincente et al, 2012) in contrasted fuel and meteorological conditions Despite these recent studies, the characterisation of the chemical compounds in smoke remains incomplete, in particular for Mediterranean fires, mainly due to the extreme difficulties in obtaining smoke samples from wildland fires
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