ESTIMATED IMPACT OF AGUNG, EL-CHICHON AND PINATUBO VOLCANIC-ERUPTIONSON GLOBAL AND REGIONAL TOTAL OZONE AFTER ADJUSTMENT FOR THE QUASI-BIENNIAL OSCILLATION (QBO)

Dobson total-ozone data are used to compare the impact on global and r egional total ozone of Agung, El Chichon and Pinatubo volcanic eruptio ns taking into account the quasi-biennial oscillation (QBO). This is d one by comparing the total-ozone variation following the 3 eruptions w ith the average quasi-biennial variation in total ozone obtained by ap plying the superposed epoch method to the 13 QBO cycles between 1958 a nd 1995 which do not include these 3 eruptions. Confidence estimates a re based on the 2-standard-deviation value of the 13 comparisons. The largest volcanic impact on total ozone is in the European region, with significant (at the 5% level) total-ozone decreases of about 5% follo wing Agung and El Chichon, and 8% following Pinatubo. The decreases in the north polar zone, Russia, North America and Asia are 5-6% followi ng Pinatubo and 2-3% following El Chichon. In the tropics the ozone de crease is less than 2% following all 3 eruptions, and there is little consistent impact on south temperate or south polar total ozone. Compa risons are made between these findings and those obtained by others us ing satellite data.