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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 22 Mar 2019

Submitted as: research article | 22 Mar 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Stratospheric ozone trends for 1985–2018: sensitivity to recent large variability

William T. Ball1,2, Justin Alsing3,4, Johannes Staehelin1, Sean M. Davis5, Lucien Froidevaux6, and Thomas Peter1 William T. Ball et al.
  • 1Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology Zurich, Universitaetstrasse 16, CHN, 8092 Zurich, Switzerland
  • 2Physikalisch-Meteorologisches Observatorium Davos World Radiation Centre, Dorfstrasse 33, 7260 Davos Dorf, Switzerland
  • 3Oskar Klein Centre for Cosmoparticle Physics, Stockholm University, Stockholm 106 91, Sweden
  • 4Physics Department, Blackett Laboratory, Imperial College London, SW7 2AZ, UK
  • 5NOAA Earth System Research Laboratory Chemical Sciences Division, Boulder, CO, USA
  • 6Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Abstract. The Montreal Protocol has successfully prevented catastrophic losses of stratospheric ozone, and signs of recovery are now evident. Nevertheless, recent work suggests that ozone in the lower stratosphere (< 24 km) continued to decline over 1998–2016, offsetting recovery at higher altitudes and preventing a statistically significant increase in quasi-global (60° S–60° N) total column ozone. In 2017, a large lower stratospheric ozone resurgence over less than 12 months was estimated (using a chemistry-transport model; CTM) to have wiped out the long-term decline in the quasi-global integrated lower stratospheric ozone column. Here, we extend the analysis of space-based ozone observations to December 2018 using the BASICSG ozone composite. We find that the observed 2017 resurgence was only around half that modelled by the CTM, was of comparable magnitude to other strong inter-annual changes in the past, and restricted to southern hemispheric mid-latitudes (SH; 60° S–30° S). In the SH mid-latitude lower stratosphere, the data suggest that by the end of 2018 ozone is still likely lower than in 1998 (probability ~ 80 %). In contrast, tropical and northern hemisphere (NH) ozone continue to display ongoing decreases, exceeding 90% probability. Robust tropical (> 95 %, 30° S–30° N) decreases dominate the quasi-global integrated decrease (99 % probability); the integrated tropical stratospheric column (1–100 hPa, 30° S–30° N) displays a significant overall decrease, with 95 % probability. These decreases do not reveal an inefficacy of the Montreal Protocol. Rather, they suggest other effects to be at work, mainly dynamical variability on long or short timescale, counteracting the protocol's regulation of halogenated ozone depleting substances (hODS). We demonstrate that large inter-annual mid-latitude variations (30° –60° ), such as the 2017 resurgence, are driven by non-linear QBO phase-dependent seasonal variability. However, this variability is not represented in current regression analyses. To understand if observed lower stratospheric decreases are a transient or long-term phenomenon, progress needs to be made in accounting for this dynamically-driven variability.

William T. Ball et al.
Data sets

BASIC-SG ozone composite J. Alsing and W. T. Ball

William T. Ball et al.
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Publications Copernicus
Short summary
We analyse long-term stratospheric ozone (60° S–60° N) trends over 1985–2018. Previous work suggested lower stratosphere ozone declined over 1998–2016. We demonstrate that a large ozone upsurge in 2017 is likely related to QBO variability, but that lower stratospheric ozone trends likely remain lower in 2018 than in 1998. Tropical stratospheric ozone (30° S–30° N) shows highly probable decreases in both the lower stratosphere and in the integrated stratospheric ozone layer.
We analyse long-term stratospheric ozone (60° S–60° N) trends over 1985–2018. Previous work...