Radar Observations of a Major Industrial Fire

Abstract

On 23 May 1996, a Montreal suburban paint factory containing several hundred thousand gallons of paints, solvents, and other chemicals burned to the ground in a spectacular fire. The smoke plume from the fire was readily detected by three radars operated by McGill University for routine observations of the atmosphere. An S-band (10-cm wavelength) scanning radar provided a plan view of the plume from the time of its initial appearance over the plant until the fire was finally extinguished. These data reveal the history of the plume, showing how it meandered and spread as it was advected downwind. The plume passed directly over the site of two vertically pointing radars, one a high-resolution X-band radar (3-cm wavelength) and the other a UHF (33-cm wavelength) wind profiler. Doppler spectra of the smoke echoes in the vertical beam of the profiler indicated predominantly downward velocities, but it was not possible to distinguish in the spectra between scattering by settling particles and scattering by the refractively perturbed air. The reflectivity of the plume in the vertical beam of the wind profiler, expressed in terms of the rain-equivalent reflectivity factor, had values up to 40 dBZ. At the shorter wavelength of the X-band radar, the reflectivity factors were less by amounts ranging from 20 to more than 30 dBZ. The difference in reflectivity can probably be accounted for by a combination of 1) the presence in the plume of particles on the order of 10 mm in diameter, which are too large to satisfy the Rayleigh scattering approximation at the shorter wavelength, and 2) a strongly perturbed structure of atmospheric refractivity, caused by the heating and turbulent mixing generated by the fire and creating a strong echo at the longer wavelength.