Example: Haze from forest fires

This is an example of the ceilometer and airplane optical extinction measurements used to examine elevated haze from a forest fire. (Optical extinction gives us a measurement of how hazy it is.)

Satellite image of smoke plumes

Satellite image for June 14, 1996, at 1545 EST showing the forest fire plumes responsible for the elevated haze layer over Montreal.

Graph: Extinction calculation vs airplane-derived

Comparison plot of airplane and ceilometer extinction profiles: The ceilometer is located in downtown Montreal on the McGill University campus. The aircraft sounding was taken over a rural region about 80 km to the southwest of the ceilometer. The extinction profiles show a good agreement up to about 800 m. Above that, the airplane measurements increase rather steadily to a maximum of 0.2/km at 2.6 km. The ceilometer profiles show a stronger maximum at a lower altitude that corresponds closely to the top of the mixing layer over the city as indicated by the McGill UHF profiler.

The elevated layer of strong extinction is uncommon and is accounted for by a smoke plumes shown in the above satellite image. The smoke appears to be concentrated more at the top of the mixing layer over the city than over the country where the airplane took its sounding. This suggests the possiblity of the deeper urban mixing layer pulling down the elevated smoke layer into the top of the mixing layer. Magnitudes of the extinction coefficients measured by the two systems are comparable, lending confidence to the ceilometer estimates.


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