Halogen occultation experiment and stratospheric aerosol and gas experiment II observations of tropopause cirrus and aerosol during the 1990s

Averages of Halogen Occultation Experiment (HALOE) aerosol extinction at 121 hPa for 1993-1999 and Stratospheric Aerosol and Gas Experiment (SAGE II) aerosol extinction between 100 and 140 hPa for 1987-1999 are analyzed in the tropics (20°S-20°N). Multiple wavelength techniques for HALOE and SAGE II data are used to distinguish cirrus from aerosol observations following the eruption of Mount Pinatubo in 1991. SAGE II and HALOE cirrus extinction values are 34 and 28% less, respectively, in 1993 than in 1995-1999, while aerosol extinction decreases over the same time period. SAGE II and HALOE decreases in the frequency of occurrence of cirrus in 1993 are qualitatively similar to the SAGE II decreases in the frequency of occurrence of cirrus, discussed by Wang et al. [1995], after the eruption of El Chichon. Tropopause temperature anomalies in 1993 most likely do not account for the decrease in cirrus observed in 1993 by both the HALOE and SAGE II experiments.