Aircraft latitude survey measurements of the El Chichon eruption cloud

Aerosol optical thicknesses were derived from solar spectral extinction measurements. These were made with a sunphotometer on board the NASA Convair 990 aircraft during May, July and December 1982 over a range of latitudes covered by the flight mission. Large increases in the optical thicknesses over the background levels for the stratosphere were found at all latitudes where observations were made; these are attributed to the El Chichon eruption cloud. The latitudinal variation of the optical thickness in May and July shows a maximum in the vicinity of the eruption, a minimum near 30°N and no appreciable change further north of the minimum. This is indicative of a thick portion of the cloud being confined between 0° and 30°N latitude. In December, the maximum was found near 8°N, the minimum near 25°N and an increase north of the minimum. The spectral dependence of the aerosol optical thickness which is different on one side of the 30°N latitude from the other suggests that the two portions of the cloud have different size distributions of aerosols.