TEMPORAL CHANGES OF MOUNT-PINATUBO AEROSOL CHARACTERISTICS OVER NORTHERN MIDLATITUDES DERIVED FROM SAGE-II EXTINCTION MEASUREMENTS

The June 12-16, 1991, eruption of Mount Pinatubo in the Philippines in jected an estimated 20 Mt of sulfur dioxide gas well into the stratosp here and is the largest volcanic event recorded in recent history. The Stratospheric Aerosol and Gas Experiment (SAGE) II satellite has prov ided unprecedented information On the evolution of the Pinatubo aeroso l since its eruption. The Pinatubo aerosol size distributions are infe rred from SAGE II extinction measurements using a randomized minimizat ion search technique in the radii range of 0.1-0.8 mu m in 0.1-mu m in crements. The Pinatubo aerosol characteristics between 13 and 30 km an d columnar characteristics in a unit column between 15 and 25 km are t hen derived. The latitudinal span is between 30 degrees and 60 degrees N from March 1991 to March 1994. During this period, the maximum surf ace area was observed to exceed 50 mu m(2) cm(-3). The vertically aver aged surface areas were of the order of 27.74 +/- 12 mu m(2) cm(-3) in March 1993 at a height of 14.5 km. The corresponding averaged mass lo ading was of the order of 4.23 +/- 1.37 mu g m(-3). During March 1994, the peak surface areas and mass loading at 14.5 km were of the order of 9.85 +/- 3.87 mu m(2) cm(-3) and 1.02 +/- 0.28 mu g m(-3), respecti vely, still larger with respect to the volcanically cm unperturbed val ues of 0.98 +/- 0.54 mu m(2) cm(-3) and 0.12 +/- 0.04 mu g m(-3) obser ved during cm March 1991. Columnar mass loading, surface area, and num ber concentrations have approached preeruption background levels, wher eas the columnar mean effective radius is still 2-3 times greater as o f March 1994.