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Volume 17, issue 17 | Copyright

Special issue: Twenty-five years of operations of the Network for the Detection...

Atmos. Chem. Phys., 17, 10495-10513, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Sep 2017

Research article | 07 Sep 2017

Attribution of recent ozone changes in the Southern Hemisphere mid-latitudes using statistical analysis and chemistry–climate model simulations

Guang Zeng1, Olaf Morgenstern1, Hisako Shiona2, Alan J. Thomas3, Richard R. Querel3, and Sylvia E. Nichol1 Guang Zeng et al.
  • 1National Institute of Water and Atmospheric Research, Wellington, New Zealand
  • 2National Institute of Water and Atmospheric Research, Christchurch, New Zealand
  • 3National Institute of Water and Atmospheric Research, Lauder, New Zealand

Abstract. Ozone (O3) trends and variability from a 28-year (1987–2014) ozonesonde record at Lauder, New Zealand, have been analysed and interpreted using a statistical model and a global chemistry–climate model (CCM). Lauder is a clean rural measurement site often representative of the Southern Hemisphere (SH) mid-latitude background atmosphere. O3 trends over this period at this location are characterised by a significant positive trend below 6km, a significant negative trend in the tropopause region and the lower stratosphere between 9 and 15km, and no significant trend in the free troposphere (6–9km) and the stratosphere above 15km. We find that significant positive trends in lower tropospheric ozone are correlated with increasing temperature and decreasing relative humidity at the surface over this period, whereas significant negative trends in the upper troposphere and the lower stratosphere appear to be strongly linked to an upward trend of the tropopause height. Relative humidity and the tropopause height also dominate O3 variability at Lauder in the lower troposphere and the tropopause region, respectively. We perform an attribution of these trends to anthropogenic forcings including O3 precursors, greenhouse gases (GHGs), and O3-depleting substances (ODSs), using CCM simulations. Results indicate that changes in anthropogenic O3 precursors contribute significantly to stratospheric O3 reduction, changes in ODSs contribute significantly to tropospheric O3 reduction, and increased GHGs contribute significantly to stratospheric O3 increases at Lauder. Methane (CH4) likely contributes positively to O3 trends in both the troposphere and the stratosphere, but the contribution is not significant at the 95% confidence level over this period. An extended analysis of CCM results covering 1960–2010 (i.e. starting well before the observations) reveals significant contributions from all forcings to O3 trends at Lauder – i.e. increases in GHGs and the increase in CH4 alone all contribute significantly to O3 increases, net increases in ODSs lead to O3 reduction, and increases in non-methane O3 precursors cause O3 increases in the troposphere and reductions in the stratosphere. This study suggests that a long-term ozonesonde record obtained at a SH mid-latitude background site (corroborated by a surface O3 record at a nearby SH mid-latitude site, Baring Head, which also shows a significant positive trend) is a useful indicator for detecting atmospheric composition and climate change associated with human activities.

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The long-term ozonesonde record from Lauder, New Zealand, which covers 1987 to 2014, shows a significant positive trend in lower tropospheric ozone, and a significant negative trend in the tropopause region. We conduct a statistical and chemistry–climate model analysis to identify the causes of these trends. We attribute these trends to anthropogenic influences and large-scale dynamical effects such as increasing tropopause height and an increase in stratosphere–troposphere exchange.
The long-term ozonesonde record from Lauder, New Zealand, which covers 1987 to 2014, shows a...