| A global climatology has been produced on the stratospheric aerosol that spans nearly 15 years, from December 1984 to August 1999. The climatology includes values and uncertainties of measured extinction and optical depth from 0.385 mum to 12.82 mum, as well as retrieved particle effective radius Reff, distribution width sigmag, surface area S and volume V. As a basis for aerosol retrievals, a multi-wavelength Look-Up-Table (LUT) algorithm has been developed that uses a combination of 4wavelength Stratospheric Aerosol and Gas Experiment (SAGE) II extinction spectra (0.385--1.02 gym) and the Cryogenic Limb Array Etalon Spectrometer (CLASS) 7.96 and 12.82 gm extinction measurements. The LUT matches SAGE II/CLASS extinction ratios to pre-computed ratios that are based on a range of unimodal lognormal size distributions. By varying the distribution width, the uncertainties in measured extinction are propagated to corresponding uncertainties in Reff, S and V. The LUT includes an altitude- and time-dependent procedure to estimate and remove bias introduced by assuming a unimodal functional form. Bias correction reduces uncertainty in Reff, S and V by approximately 7%, 5% and 1%, respectively. This suggests that aerosol volume, and to a lesser extent surface area, are not as sensitive to a priori assumptions about distribution shape as retrievals of Reff. Aerosol retrievals show notable increases after most major volcanic eruptions, with increases in Reff lagging increases in other parameters. Post-volcanic increases in sigmag, indicative of broader size distributions, are consistent with sudden increases in both small and large particle sizes. After Pinatubo, retrieved Reff and sigmag took nearly 5 years to return to pre-eruption values, while slightly shorter recovery times are obtained for S and V. Seasonal variations in S and V are observed at high latitudes (with high values occurring in winter), but are less obvious in Reff. Latitudinal banding is often noted in retrievals in a layer just above the tropopause, with high values occurring in the tropics and at high latitudes. The overall uncertainty in retrievals is approximately +/-20% for S and V, with slightly smaller values for R eff. Results were compared to several previously developed stratospheric aerosols climatologies and, with few exceptions, agree well with these climatologies. |
