INFRARED-ABSORPTION BY VOLCANIC STRATOSPHERIC AEROSOLS OBSERVED BY ISAMS

The Improved Stratospheric and Mesospheric Sounder (ISAMS) aboard the Upper Atmosphere Research Satellite (UARS) senses in 14 wideband channels in the infrared. The absorption by the Mt. Pinatubo aerosol cloud for nine of the channels was averaged over heights from 20 km to 30 km for a 60-degrees latitude band centred on the Equator. The absorption spectrum for sulphuric acid-water aerosols was calculated for wavelengths from 4 mum to 17 mum and investigated as a function of the particle size distribution and the particle composition. The infrared spectrum is shown to be more sensitive to changes in particle composition than to drop size; the ISAMS results are consistent with drops composed of a 59% to 77% solution of sulphuric acid in water.