Articles | Volume 15, issue 17
Atmos. Chem. Phys., 15, 9965–9982, 2015

Special issue: Changes in the vertical distribution of ozone – the SI2N report...

Atmos. Chem. Phys., 15, 9965–9982, 2015

Research article 07 Sep 2015

Research article | 07 Sep 2015

Past changes in the vertical distribution of ozone – Part 3: Analysis and interpretation of trends

N. R. P. Harris1, B. Hassler2,3, F. Tummon4, G. E. Bodeker5, D. Hubert6, I. Petropavlovskikh2,7, W. Steinbrecht8, J. Anderson9, P. K. Bhartia10, C. D. Boone11, A. Bourassa12, S. M. Davis2,3, D. Degenstein12, A. Delcloo13, S. M. Frith14, L. Froidevaux15, S. Godin-Beekmann16, N. Jones17, M. J. Kurylo18, E. Kyrölä19, M. Laine19, S. T. Leblanc15, J.-C. Lambert6, B. Liley20, E. Mahieu21, A. Maycock1, M. de Mazière6, A. Parrish22, R. Querel20, K. H. Rosenlof3, C. Roth12, C. Sioris12, J. Staehelin4, R. S. Stolarski23, R. Stübi24, J. Tamminen19, C. Vigouroux6, K. A. Walker25, H. J. Wang26, J. Wild27,28, and J. M. Zawodny29 N. R. P. Harris et al.
  • 1University of Cambridge Chemistry Department, Cambridge, UK
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 3Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 4ETH Zurich, Zurich, Switzerland
  • 5Bodeker Scientific, Alexandra, New Zealand
  • 6Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium
  • 7Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, CO,~USA
  • 8Deutscher Wetterdienst, Hohenpeissenberg, Germany
  • 9Hampton University, Hampton, VA, USA
  • 10NASA Goddard Space Flight Center, Silver Spring, MD, USA
  • 11University of Waterloo, Department of Chemistry, Waterloo, Canada
  • 12Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
  • 13Royal Meteorological Institute of Belgium, Brussels, Belgium
  • 14Science Systems and Applications, Inc., Lanham, MD, USA
  • 15California Institute of Technology, Jet Propulsion Laboratory, Wrightwood, CA, USA
  • 16Centre National de la Recherche Scientifique, Université de Versailles Saint-Quentin-en-Yvelines, Guyancourt, France
  • 17School of Chemistry, University of Wollongong, Australia
  • 18Universities Space Research Association/Goddard Earth Sciences, Technology and Research, Greenbelt, MD, USA
  • 19Finnish Meteorological Institute, Helsinki, Finland
  • 20National Institute of Water and Atmospheric Research (NIWA), State Highway 85, Lauder, New Zealand
  • 21Institute of Astrophysics and Geophysics, University of Liège, Liège, Belgium
  • 22Department of Astronomy, University of Massachusetts, Amherst, MA, USA
  • 23John Hopkins University, Baltimore, MD, USA
  • 24Federal Office of Meteorology and Climatology, MeteoSwiss, 1530 Payerne, Switzerland
  • 25University of Toronto, Toronto, Canada
  • 26Georgia Institute of Technology, Atlanta, GA, USA
  • 27Innovim, Greenbelt, MD, USA
  • 28NOAA/NWS/NCEP/Climate Prediction Center, College Park, MD, USA
  • 29NASA Langley Research Center, MS-475, Hampton, VA 23681-2199, USA

Abstract. Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine – EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10 % per decade at mid-latitudes and closer to −5 % per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and ground-based records have been revised.

There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2 % per decade in mid-latitudes and ~ 3 % per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties.

Short summary
Trends in the vertical distribution of ozone are reported for new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere peaked in the second half of the 1990s. We examine the trends before and after that peak to see if any change in trend is discernible. The previously reported decreases are confirmed. Furthermore, the downward trend in upper stratospheric ozone has not continued. The possible significance of any increase is discussed in detail.
Final-revised paper