Lidar observations of the El Chichón aerosol at a southern latitude station

Abstract

Lidar observations at Sao José dos Campos (23ºS, 46°W) show that the El Chichón dust cloud had reached this latitude by mid-July, 1982. The first measurement made after the eruption showed two layers with scattering ratios of 1.8 and 2. 7 at 18 and 24 km respectively, as compared with pre-injection values of about 1.2. These values refer to a wavelength of 5 890 Jl, and are for a profile obtained on July 9th. Measurements made in subsequent months showed large fluctuations, particularly in the upper !ayer, where the scattering ratio varied between 1.2 and 5. The lower !ayer varied much less than the upper, with the result that the integrated backscatter, a measure of the total stratospheric aerosol burden; remained roughly constant until late August, when it increased from about 3 x 10"4 SR-1 to about 1 x 10-3 SR-1 . Subsequent to this date the integrated aerosol oscillated around a value of about 8 x 10-4 SR-1 until midMarch 1983, since when it has decreased to about 5 x 10-4 SR-1 • The height of the upper !ayer decreased fairly uniformly with time until late November, when it reached 20 km, by which time it had merged with the lower layer. In 1983 the !ayer has again shown a bifurcated structure with a lower peak close to 18 km andan upper one 2 to 4 km higher.