EVOLUTION OF THE MT-PINATUBO AEROSOL OVER ANTARCTICA INFERRED FROM SAGE-II EXTINCTION MEASUREMENTS

This study focuses on the evolution and stratospheric settling of the Mt. Pinatubo volcanic aerosol. The volcanic aerosol characteristics ar e inferred from the Stratospheric Aerosol and Gas Experiment (SAGE) II extinction measurements using a modified randomized minimization sear ch technique (RMST) between 13-30 km in the radii range between 0.10-0 .80 mu m. The temporal span of this study is between the date of erupt ion to early 1994 at latitudes poleward of 50 degrees S. The 1991 erup tion of Mt. Pinatubo resulted in the enhancement of the derived quanti ties with the existence of a large particle mode superimposed on the s mall background mode. This resulted in an order of magnitude increase in column number concentration, a 5-fold increase in column surface ar ea, and greater than 20-fold increase in column mass loading during th e austral summer of 1992. The averaged column effective radius is arou nd 0.25 mu m in 1994, still greater than the 0.15 mu m observed in 199 1 (background). The column mass loading has decreased 25 mg m(-2) over two years between 1992-94. Column bi-modal size distributions were ev ident from austral spring 1991 through the austral summer of 1994 with small mode radii less than or equal to 0.20 mu m and large mode betwe en 0.30-0.60 mu m. Effects of the polar vortex are observed during eac h austral spring since the eruption. Aerosol settling and decay in the presence of horizontal and vertical transport is observed during each austral spring. Column number concentrations have reached pre-eruptio n background levels whereas mass loading, surface area, and mean effec tive radius are still elevated as of early 1994.