Onset of stratospheric ozone recovery in the Antarctic ozone hole in assimilated daily total ozone columns.

In this paper we evaluate the long-term changes in ozone depletion within the Antarctic ozone hole using a 37 years (1979–2015) of daily ozone mass deficits (OMDs) derived from assimilated total ozone column data. For each year an “average daily OMD” is calculated over a 60 day preferential time period (day of year 220–280). Excluding years with a reduced polar stratospheric cloud (PSC) volume (the so-called PSC-limited years), the 1979–2015 time series of spatially integrated average daily OMD correlates very well with long-term changes in equivalent effective stratospheric chlorine (EESC; R2 = 0.89). We find a corresponding statistically highly significant post-2000 decrease in OMD of −0.77 ± 0.17 megaton (trend significance of 9.8σ), with an associated post-2000 change in OMD of approximately −30%, consistent with the post-2000 change in EESC relative to 1980 EESC levels of approximately −30%. The post-2000 trend significance is robust to the choice of start year. The spatial distribution of the average daily OMD trends reveals a vortex-core region (approximately covering the region [90°W–0°–90°E/75°S–85°S]) largely unaffected by dynamics with a post-2000 trend significance of >8σ, and a vortex-edge region in which the trend is locally strongly affected by vortex dynamics though not spatially integrated over the whole vortex-edge region (trend significance >9σ). For the trend significance we do not find consistent evidence for long-term changes in wave driving, vortex mixing, preozone hole conditions, or the applied assimilation method, playing a role. Our observation/assimilation-based analysis provides robust evidence of a post-2000 statistically highly significant decrease in the average daily OMD that is consistent with the long-term decrease in ozone-depleting substances since 2000, following international emission regulations.