An estimated 20--30 megatons of SO2 and crustal material was injected into the stratosphere during June 12--16, 1991, by the eruption of Mount Pinatubo (15.1¿N, 120.4¿E). The impact on Antarctic aerosol characteristics is of utmost concern owing to the seasonality in the observed ozone depletion and climate implications. This study focuses on Antarctic stratospheric aerosol characteristics during three temporal periods: September 23--30, September 30 to October 13, and November 13--27, 1991, at latitudes poleward of 60¿S for vertically averaged characteristics, and at latitudes poleward of 50¿S for temporal and spatial characteristics. Stratospheric aerosol characteristics are inferred from the Stratospheric Aerosol and Gas Experiment (SAGE) II measurements using a modified randomized minimization search technique (RMST). Aerosol characteristics such as size distribution, number concentration, mass loading, surface area concentration, and radial characteristics are derived between 15 and 30 km for particles having radii between 0.1 and 0.8 μm. Results indicate that aerosol size distributions between 15 and 30 km are bimodal in several instances for all three time periods and can be fitted with the sum of two lognormal distributions. Larger concentrations are observed for particles of all sizes between 18 and 30 km during November 1991, signaling the arrival of the Mount Pinatubo plume.

An order of magnitude increase in concentration is observed for particles with radii between 0.1 and 0.2 μm and between 0.7 and 0.8 μm. Vertical aerosol profiles show that the peak in aerosol concentration shifted to a higher altitude between 21 and 26 km as compared to the preplume peak between 15 and 18 km. Using the displacement as a function of time for a mass loading of 1.7 μg m-3 isopleth, we estimated meridional velocity ≈0.9 m s-1, zonal velocity ≈16 m s-1, and downward vertical velocity of 0.5 cm s-1 during September to mid-October, 1991, and 0.3 cm s-1 during mid to late November 1991. The mass deposition flux was estimated to be 9¿10-13 g cm-2 s-1. The peeling of segments of the Pinatubo aerosol was found near the outer edge of the circumpolar vortex wall centered around 56¿S. Meridional wave activity was also observed poleward of 56¿S. Two meridional separation regimes were found: between 56¿ and 62¿S and between 62¿ and 66¿S. These two regions represent different segments of the vortex edge. In the first region we found wavelike isopleths with rising motions between 55¿ and 58¿S and sinking motions thereafter. In the second region, rising motions were located between 60¿ and 63¿S and sinking motions at latitudes poleward of 63¿S. In contrast to previous reports, we found an indication of entrainment of volcanic aerosol into the vortex edge. The Mount Pinatubo aerosol is an effective tracer of south polar transport. ¿ American Geophysical Union 1995