Ozone depletion at northern and southern latitudes derived from January 1979 to December 1991 Total Ozone Mapping Spectrometer data

Abstract

Long‐term ozone depletion rates (percentage change) have been computed from 13 years of Nimbus 7/Total Ozone Mapping Spectrometer (TOMS) data as a function of latitude, longitude, and month for the period January 1, 1979, to December 31, 1991. In both hemispheres the amount of ozone has decreased at latitudes above 30° by amounts that are larger than predicted by homogeneous chemistry models for the 13‐year time period. The largest rates of ozone decrease occur in the southern hemisphere during winter and spring, with partial recovery during the summer and autumn. Outside of the Antarctic ozone hole region, the 12‐year ozone depletion rates reach 8–10% per decade during the winter and spring at 55°S. Ozone depletion rates in excess of 7% per decade occur over populated regions in the southern hemisphere poleward of 45°S (southern Argentina and the tip of New Zealand) for 7 months of the year. Similar rates of decrease occur during northern winter and spring (6–8% at 55°N) over large populated regions. The enhanced zonal average ozone depletion rates at northern mid‐latitudes (40–50°N) during January, February, and March, that correspond to five geographically localized regions of high ozone depletion rates, are probably associated with long‐term dynamical or temperature changes. Only the equatorial band between ±20° shows little or no long‐term ozone change since January 1979. Ozone time series data have been examined for effect of volcanic eruptions on stratospheric ozone observed by TOMS, with only the Mount Pinatubo stratospheric aerosol injection affecting ozone amounts for a few months after the eruption in June 1991. The TOMS data show no ozone perturbation after the El Chichon eruption, or after any of the other smaller equatorial eruptions, that cannot be explained by interference effects between the annual, El Nino/Southern Oscillation, and Quasi‐Biennial Oscillation cycles. The effect of the stratospheric aerosol scattering phase function is clearly seen in the high spatial resolution TOMS ozone data after El Chichon and Mount Pinatubo. Errors caused by the short‐term presence of stratospheric aerosols in the TOMS zonally averaged ozone data are less than 1% before correction, and have no significant effect on ozone trend determination.