EARLY STRATOSPHERIC EFFECTS OF THE PINATUBO ERUPTION

The Pinatubo eruptions of June 1991 introduced large plumes into the local stratosphere. On several occasions, volcanic gases and particles reached altitudes of about 30 km, quickly spreading to the west. Twenty days after the first eruption, the volcanic aerosol cloud was detected by lidar 14 km over Frascati, Italy. The upper portion of the cloud was observed for the first time on September 4, 1991, at an altitude of 23 km. Vertical and temporal evolution of the cloud, as observed from Frascati, are in agreement with trajectories estimated by means of northern hemisphere, stratospheric wind maps. Temperature records and characteristics of the cloud during the first 6 months following the eruption are reported. These characteristics are also compared to the ones of El Chichon, whose eruption, in 1982, rated amongst the largest in the century. This first analysis shows that, three and a half months after the eruption, the aerosol perturbation generated by Pinatubo reached and exceeded the maximum loads, recorded 11 months after the El Chichon event. However, by the end of the year, the aerosol columns of the two events tend towards comparable magnitudes.