Evidence of the Pinatubo volcanic eruption on the distribution of ozone over the tropical Indian region

Abstract

Three independent sets of experimental data for ozone obtained by balloon-borne ozonesondes and Dobson spectrophotometer during the period 1979-1998 are analyzed over the tropical Indian region covering two stations, Delhi (28°N, 77°E) and Pune (18°N, 73.5°E), in search of volcanic signals after the Mount Pinatubo eruption of 1991. These data sets are analyzed using a regression model, based on multiple function regression theory, which takes into account several natural and anthropogenic signals in order to detect a relatively smaller magnitude, sporadic effect. To study the volcanic effects on the vertical structure of ozone, data sets are independently analyzed for four different predefined Umkehr layers from 15 to 33 km. The total ozone amounts obtained by Dobson spectrophotometer over these two stations are revisited and analyzed using the above regression model. A maximum decrease of the order of 4-7 Dobson units (DU) in the altitude range 15-24 km following 3-4 months of eruption and a maximum increase of the order of 2-3 DU for the altitude range 24-33 km immediately after the eruption have been observed in ozone amounts over these two tropical stations. The total ozone amount measurement indicates a decrease of about 5-6% during the period effected by the Pinatubo eruption. The decreasing trend in ozone content is found to exist up to a maximum of 1.5 years from the time of eruption. The similarity of the results obtained from the three sets of data analyzed affirms the effect of volcanic eruption over the tropical Indian region.