First stage of Antarctic ozone recovery

摘要

Ozone within the springtime Antarctic vortex is affected by both chemical and dynamical processes. We use correlations between monthly means of total ozone columns and temperatures in the vortex core and the vortex edge (or collar) regions to construct ozone anomaly time series for September and October, which mainly reflect variations in ozone due to chemical forcing. The ozone anomaly time series, obtained from ground-based Dobson/Brewer column measurements, reveal a statistically significant leveling off of total ozone, relative to the previous rate of decline, since 1997. The second derivative with respect to time of stratospheric halogen loading in the Antarctic vortex reached a well-defined minimum in 1997, marking the time when the chemical forcing of polar ozone loss started leveling off. Vertical profiles of ozone in the Antarctic vortex from SAGE II and ozonesondes show that near-zero levels of ozone have sometimes been reached in the core of the vortex each October, between the 380 and 500 K isentropes, since 1992. We have accounted for this so-called loss saturation effect in our analysis by comparing the frequency distribution of measured ozone with the distribution expected from a reconstruction of ozone that hypothetically allows ozone abundances to drop below zero. This approach indicates that changes in stratospheric halogen loading, not the loss saturation effect, are the primary cause of the recent leveling off of the total ozone anomaly time series. This analysis indicates that total column ozone within the Antarctic vortex core and collar regions has reached the first stage of recovery as defined by the World Meteorological Organization: a statistically significant reduction in the rate of decline that is clearly attributable to decreases in the abundance of ozone-depleting substances brought about by the Montreal Protocol.