An Aerosol Climatology From SAGE II and CLAES: Comparisons

This work reviews several previously developed stratospheric aerosol climatologies and compares them with aerosol properties obtained with our Look-Up-Table (LUT) technique, which uses data from the Stratospheric Aerosol and Gas Experiment (SAGE II) and the Cryogenic Limb Array Etalon Spectrometer (CLAES) instruments. Direct comparisons are made with climatologies developed by Deshler et al., Hitchman et al., Lambert et al., Kent et al. and Thomason et al., as well as with a retrieval technique developed by Yue. Unlike some earlier climatologies, the LUT climatology spans nearly 15 years, from December 1984 to August 1999, and includes values as well as associated uncertainties of measured extinction and optical depth, and retrieved effective radius, surface area, volume and distribution width - an aerosol parameter rarely, if ever, available. With some exceptions, LUT retrievals agree well with most previous climatologies. For example, agreement is good between LUT retrieved surface area and Deshler's balloon-borne measurements, where available. However, there are a few important discrepancies. For example, the Thomason et al. values of surface area, derived by applying Principal Component Analysis (PCA) to SAGE II data, are less than LUT retrievals during near-background periods (e.g., 1989 to mid-1991, and after 1996), and greater than LUT retrievals in the peak of the Pinatubo plume. In the peak of the plume near 20 km, the PCA/SAGE II estimates also exceed maximum estimates by Lambert et al. based on CLAES/ISAMS data and by Optical Particle Counter estimates. We suggest that the smaller post-Pinatubo surface areas obtained by the SAGE II/CLAES LUT and CLAES/ISAMS techniques reflect the constraint on particle size obtained when SAGE II measurements are supplemented with those at longer wavelengths from another satellite.