Evolution of the Mt. Pinatubo aerosol over Antarctica inferred from sage II extinction measurements

Abstract

This study focuses on the evolution and stratospheric settling of the Mt. Pinatubo volcanic aerosol. The volcanic aerosol characteristics are inferred from the Stratospheric Aerosol and Gas Experiment (SAGE) II extinction measurements using a modified randomized minimization search technique (RMST) between 13–30 km in the radii range between 0.10–0.80 μm. The temporal span of this study is between the date of eruption to early 1994 at latitudes poleward of 50°S. The 1991 eruption of Mt. Pinatubo resulted in the enhancement of the derived quantities with the existence of a large particle mode superimposed on the small background mode. This resulted in an order of magnitude increase in column number concentration, a 5-fold increase in column surface area, and greater than 20-fold increase in column mass loading (luring the austral summer of 1992. The averaged column effective radius is around 0.25 μm in 1994, still greater than the 0.15 μm observed in 1991 (background). The column mass loading has decreased 25 mg m −2 over two years between 1992–1994. Column bi-modal size distributions were evident from austral spring 1991 through the austral summer of 1994 with small mode radii ⩽ 0.20 μm and large mode between 0.30 – 0.60 μm. Effects of the polar vortex are observed during each 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-eruption background levels whereas mass loading, surface area, and mean effective radius are still elevated as of early 1994.