Spectral extinction of direct solar radiation by the El Chichon cloud during December 1982

Stratospheric aerosol optical depths at five discrete solar wavelengths are calculated from solar extinction measurements made on board a NASA (National Aeronautics and Space Administration) Convair 990 aircraft between 55°N and 6°S latitude during December 1982. The latitudinal and spectral variations of the aerosol optical depths, presumed to be due to effluents from the eruptions of El Chichon, show a north to south separation into two components, each with a characteristic spectral signature. The average aerosol optical depth, both spatially and spectrally, was 0.10 ± 0.01. Calculations indicate that this enhancement is sufficient to cause an 18% decrease in direct broadband solar irradiance at a representative zenith angle of 60°.