A CLIMATOLOGY OF STRATOSPHERIC AEROSOL

A global climatology of stratospheric aerosol is created by combining nearly a decade (1979-1981 and 1984-1990) of contemporaneous observati ons from the Stratospheric Aerosol and Gas Experiment (SAGE I and II) and Stratospheric Aerosol Measurement (SAM II) instruments. One goal o f this work is to provide a representative distribution of the aerosol layer for use in radiative and chemical modeling. A table of decadal average 1 mu m extinction values is included, extending from the tropo pause to 35 km and 80 degrees S to 85 degrees N, which allows estimati on of surface area density. We find that the aerosol layer is distinct ly volcanic in nature and suggest that the decadal average is a more u seful estimate of future aerosol loading than a ''background'' loading , which is never clearly achieved during the data record. This climato logy lends insight into the general circulation of the stratosphere. L atitude - altitude sections of extinction ration at 1 mu m are shown, averaged by decade, season, and phase of the quasi-biennial oscillatio n (QBO). A tropical reservoir region is diagnosed, with an ''upper'' a nd a ''lower'' transport regime. In the tropics above 22 km (upper reg ime), enhanced lofting occurs in the summer, with suppressed lofting o r eddy dilution in the winter. In the extratropics within two scale he ights of the tropopause (lower regime), poleward and downward transpor t is most robust during winter, especially in the northern hemisphere. The transport patterns persist into the subsequent equinoctial season . Ascent associated with QBO easterly shear favors detrainment in the upper regime, while relative descent and poleward spreading during QBO westerly shear favors detrainment in the lower regime. Extinction rat ion differences between the winter-spring and summer-fall hemispheres, and differences between the two phases of the QBO, are typically 20-5 0%. Dynamical implications of the aerosol distributions are explored, with focus on interhemispheric differences, strong subtropical gradien ts, and the pronounce annual cycle.