Latitude survey of aerosol optical thickness of the El Chichon eruption cloud in May 1983

Aerosol optical thicknesses calculated from solar spectral extinction measurements made with a sunphotometer on board a NASA Convair 990 aircraft in May, 1983 are presented. The measurements were obtained over the latitude range 71°N to 56°S. The latitudinal distribution of the optical thickness at 500 nm wavelength shows distinct minima of .01‐.02 at 25° latitude in both the hemispheres, a broad maximum of about 0.12 between 50°N and 60°N latitude and a maximum of about 0.1 around 10°S and 40°S latitude. The wavelength dependence of aerosol optical thickness is nearly neutral. The median radius of aerosol particles is estimated to be between 0.16µ and 0.18µ at latitudes between 12°S and 71°N, with the maximum of 0.18µ observed between the equator and 25°N latitude. A median radius in the range from 0.11µ and 0.15µ is found at latitudes south of 12°S. An aerosol mass density of .04‐.05 g/m² was estimated at latitudes between 50°N and 60°N and of .02‐.03 g/m² at other latitudes in the northern hemisphere. In the southern hemisphere it was .02‐.03 g/m² between 35°S and 40°S and .01‐.02 g/m² at other latitudes. Rough estimates of aerosol mass indicate that about 1.5 megatonnes of aerosol still persisted in the stratosphere between the equator and 25°N one year after an eruption.