A 25-year History of Aerosol Extinction Measurements by the Stratospheric Aerosol Gas Experiment Series

The Stratospheric Aerosol and Gas Experiment (SAGE) series of instruments has now produced over 25 years of aerosol extinction measurements. These instruments consist of SAM II (1978-1993), SAGE (1979-1981), SAGE II (1984-present), and SAGE III (2002-present). This period encompasses several significant volcanic perturbations of the stratosphere including those by El Chichon in 1982 and Pinatubo in 1991. Since these events are relatively rare, the record between 1978 and the present is dominated by the lengthy relaxation back to non-volcanic levels. Within this period, at least two periods have been suggested to have reached a non-volcanic level throughout the stratosphere: 1979 and after 1999. In this presentation, we will compare mean and seasonal behavior of SAGE measurements those periods and discuss the problems associated with the use of SAGE data infer changes in stratospheric levels between them. Chief among these difficulties are the long-term stability of the instruments, the cross calibration of the instruments, and dynamic range of the instruments. All of these factors are crucial in establishing confidence limits on any derived difference in stratospheric aerosol levels between these periods.