Onset of Stratospheric Ozone Recovery in the Antarctic Ozone Hole in Assimilated Daily Total Ozone Columns

Abstract

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.

Recent Decline in Extratropical Lower Stratospheric Ozone Attributed to Circulation Changes

“…Additionally, a chemical model simulation driven by MERRA-2 is used to link these trends to decadal-scale changes in stratospheric transport. While some recent studies assessed trends in total column ozone in reanalyses (Bai et al, 2017;de Laat et al, 2017), the use of a bias-corrected reanalysis to derive vertically resolved ozone trends in the LS in the context of transport patterns is a novel part of this work. However, the application of data assimilation methodology allows a relatively high vertical resolution of the reanalysis product and facilitates interpretation of the ozone behavior in terms of variability and trends in the atmospheric circulation, provided that biases resulting from step changes in its observing system are removed.…”

“…However, the application of data assimilation methodology allows a relatively high vertical resolution of the reanalysis product and facilitates interpretation of the ozone behavior in terms of variability and trends in the atmospheric circulation, provided that biases resulting from step changes in its observing system are removed. While some recent studies assessed trends in total column ozone in reanalyses (Bai et al, 2017;de Laat et al, 2017), the use of a bias-corrected reanalysis to derive vertically resolved ozone trends in the LS in the context of transport patterns is a novel part of this work.…”

Chlorine partitioning near the polar vortex edge observed with ground-based FTIR and satellites at Syowa Station, Antarctica, in 2007 and 2011

“…In the polar regions, the ozone and related atmospheric trace gas species have been intensively monitored by several measurement techniques since the discovery of the ozone hole. These measurements consist of direct observations by high-altitude aircraft (e.g., Anderson et al, 1989;Ko et al, 1989;Tuck et al, 1995;Jaeglé et al, 1997;Bonne et al, 2000), remote-sensing observations by satellites (e.g., Müller et al, 1996;Michelsen et al, 1999;Höpfner et al, 2004;Dufour et al, 2006;Hayashida et al, 2007), remote-sensing observations of OClO using a UV-visible spectrometer from the ground (Solomon et al, 1987;Kreher et al, 1996), and remote-sensing observations of ClO by a microwave spectrometer from the ground (de Zafra et al, 1989). Within these observations, ground-based measurements have the characteristic of high temporal resolution.…”

Why Do Antarctic Ozone Recovery Trends Vary?

“…Satellite observations of total column O 3 are often used because they provide excellent coverage of the high latitudes in late winter (September) and spring. Various metrics are used to calculate recovery trends from satellite column O 3 data sets: 60–90°S or 63–90°S polar cap mean O 3 (Chipperfield et al, ; Solomon et al, ; Weber et al, ), the area with column O 3 <220 DU (Solomon et al, ), and ozone mass deficits (OMDs) with respect to 220 DU O 3 (DeLaat et al, ; Pazmiño et al, ). (One Dobson Unit = 2.6867 × 10 20 molecules/m 2 .)…”