SAGE-II MEASUREMENTS OF EARLY PINATUBO AEROSOLS

SAGE II satellite measurements of the Mt. Pinatubo eruption cloud in the stratosphere during June, July, and early August 1991 show that aerosols in the tropics reached as high as 29 km altitude with most of the cloud between 20 and 25 km. The most optically thick portions of the cloud covered latitudes from 10-degrees-S to 30-degrees-N during the early part of this period. By late July, high stratospheric optical depths were observed to at least 70-degrees-N, with the high values north of about 30-degrees-N from layers below 20 km. High pressure systems in both hemispheres were observed to be correlated with the movement of volcanic material at 21 km into the westerly jet stream at high southern latitudes and similarly to high northern latitudes at 16 km. By August, the entire Southern Hemisphere had experienced a 10-fold increase in optical depth relative to early July due to layers above 20 km. Initial mass calculations using SAGE II data place the aerosol produced from this eruption at 20 to 30 megatonnes, well above the 12 megatonnes produced by El Chichon.