Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-142
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
15 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Reconciling differences in stratospheric ozone composites
William T. Ball1,2, Justin Alsing3,4, Daniel J. Mortlock4,5,6, Eugene V. Rozanov1,2, Fiona Tummon1, and Joanna D. Haigh4,7 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
3Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave, New York, NY 10010, USA
4Physics Department, Blackett Laboratory, Imperial College London, SW7 2AZ, UK
5Department of Mathematics, Imperial College London, SW7 2AZ, UK
6Department of Astronomy, Stockholms universitet, 106 91 Stockholm, Sweden
7Grantham Institute – Climate Change and the Environment, Imperial College London, SW7 2AZ, UK
Abstract. To accurately estimate decadal trends in stratospheric ozone requires stable long-term observations. Recently, several ozone composites have been published that combine observations from multiple instruments to span more than three decades. Despite this, trends disagree by latitude and altitude, even between composites built upon the same instrument data. We confirm that the leading causes of differences in decadal trend estimates lie in (i) steps in the composite timeseries when the instrument source data changes and (ii) artificial sub-decadal trends in the underlying instrument data. These artefacts introduce features that can alias with regressors in multiple linear regression (MLR) analysis; both lead to inaccurate trend estimates. Here, we aim to remove these artefacts by applying particle filtering, sequential Monte Carlo Bayesian estimation, which uses only the data itself in addition to prior knowledge about ozone variability and known problems during instrument operation. We apply the particle filter to stratospheric ozone in 10° bands from 60° S–60° N and from 46–1 hPa (~ 21–48 km) for 1985–2012. There are two main outcomes: (i) we independently identify and confirm many of the data problems previously identified, but which remain unaccounted for in existing composites; (ii) we construct an ozone composite, with uncertainties, that is free from most of these problems. To analyse the new data series, we use dynamical linear modelling (DLM), which provides a more robust estimate of long-term changes through Bayesian inference than MLR. Particle filtering and DLM, together, provide a step forward in improving estimates of decadal trends. Our results indicate a significant recovery of ozone since 1998 in the upper stratosphere, of both northern and southern mid-latitudes, in all four composites analysed, and particularly in the new particle filter composite. The particle filter results also show no hemispheric difference in the recovery at mid-latitudes, in contrast to a feature that is present, but not consistent, in the four composites. We recommend using the particle filter method to construct a new composite based not on existing composites, as we do here, but on the original instrument data: such a product would provide a further advance for the estimation of decadal changes in stratospheric ozone.

Citation: Ball, W. T., Alsing, J., Mortlock, D. J., Rozanov, E. V., Tummon, F., and Haigh, J. D.: Reconciling differences in stratospheric ozone composites, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-142, in review, 2017.
William T. Ball et al.
William T. Ball et al.
William T. Ball et al.

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Short summary
Several ozone composites show different decadal trends, even in composites built with the same data. We remove artefacts affecting trend analysis using a particle filter and construct an ozone composite, with uncertainties. We find a significant ozone recovery since 1998 in the mid-latitude upper stratosphere, with no hemispheric difference. We recommend using the particle filter to construct a composite based on the original instrument data to improve stratospheric ozone trend estimates.
Several ozone composites show different decadal trends, even in composites built with the same...
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