Past changes in the vertical distribution of ozone – Part 3: Analysis and interpretation of trends
Harris, N. R. P.
Bodeker, G. E.
Bhartia, P. K.
Boone, C. D.
Davis, S. M.
Frith, S. M.
Kurylo, M. J.
Leblanc, S. T.
de Mazière, M.
Rosenlof, K. H.
Stolarski, R. S.
Walker, K. A.
Wang, H. J.
Zawodny, J. M.
Atmospheric Chemistry and Physics
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Harris, N. R. P., Hassler, B., Tummon, F., Bodeker, G. E., Hubert, D., Petropavlovskikh, I., Steinbrecht, W., et al. (2015). Past changes in the vertical distribution of ozone – Part 3: Analysis and interpretation of trends. Atmospheric Chemistry and Physics, 15 (17), 9965-9982. https://doi.org/10.5194/acp-15-9965-2015
This is the final version of the article. It first appeared from Copernicus Publications via http://dx.doi.org/10.5194/acp-15-9965-2015
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.
The authors thank the many people who have contributed to the ozone measurement programmes over the years. The quality of their work is fundamental to the value of long-term measurement programmes and analyses of the resulting data. In particular we thank all those involved in the SI2N initiative whose research underlies the results presented here. The support of SPARC, IO3C, IGACO-O3 and NDACC was essential to the success of the initiative. Neil Harris thanks the UK Natural Environment Research Council for an Advanced Research Fellowship. Work at the Jet Propulsion Laboratory was performed under contract with the National Aeronautics and Space Administration. P. Bernath and R. Fuller are thanked for help with the access and analysis of the ACE-FTS and MLS data, respectively (as part of GOZCARDS). The ground-based data used in this publication were obtained as part of NDACC and are publicly available. Measurements at Lauder are core funded through New Zealand’s Ministry of Business, Innovation and Employment, while those at Woolongong are supported by the Australian Research Council.
External DOI: https://doi.org/10.5194/acp-15-9965-2015
This record's URL: https://www.repository.cam.ac.uk/handle/1810/254243
Attribution 2.0 UK: England & Wales
Licence URL: http://creativecommons.org/licenses/by/2.0/uk/
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