Global ozone trends from a reanalysis of TOMS data

Abstract

Analyses of 10 years of daily average total ozone data for March 15 and October 10 were carried out. These days were chosen as they correspond, respectively, to the maxima in occurrence of the polar ozone thinning phenomena in the northern and southern polar regions. Several conclusions of significance arise from these analyses. The NIMBUS-7 TOMS data provide one of the best data sets available, with which to monitor global ozone depletion. Utilizing the assumption that equatorial ozone levels remain stable, a self-consistent compensation for instrumental drift indicates a −0.70% annual drift in the TOMS data values, which needs correction. Correcting for the TOMS drift in the 1979–1988 March 15 and October 10 data shows that a global ozone depletion is occurring at the rate of 0.224% per year. These analyses show that the maximum ozone-depletion rate occurs in the polar zone containing the ozone thinning phenomena. The southern zone depletion rate is some three times greater than the northern (1.06% compared with 0.39% per year), and the rate in the southern zone remains significantly above the global depletion rate, even during absence of the ozone thinning phenomenon (0.47% per year). This decrease is alarmingly greater than predicted by scenario models.