Articles | Volume 15, issue 1
Research article
08 Jan 2015
Research article |  | 08 Jan 2015

Tracing the second stage of ozone recovery in the Antarctic ozone-hole with a "big data" approach to multivariate regressions

A. T. J. de Laat, R. J. van der A, and M. van Weele

Abstract. This study presents a sensitivity analysis of multivariate regressions of recent springtime Antarctic vortex ozone trends using a "big data" ensemble approach.

Our results indicate that the poleward heat flux (Eliassen–Palm flux) and the effective chlorine loading respectively explain most of the short-term and long-term variability in different Antarctic springtime total ozone records. The inclusion in the regression of stratospheric volcanic aerosols, solar variability and the quasi-biennial oscillation is shown to increase rather than decrease the overall uncertainty in the attribution of Antarctic springtime ozone because of large uncertainties in their respective records.

Calculating the trend significance for the ozone record from the late 1990s onwards solely based on the fit of the effective chlorine loading is not recommended, as this does not take fit residuals into account, resulting in too narrow uncertainty intervals, while the fixed temporal change of the effective chlorine loading does not allow for any flexibility in the trends.

When taking fit residuals into account in a piecewise linear trend fit, we find that approximately 30–60% of the regressions in the full ensemble result in a statistically significant positive springtime ozone trend over Antarctica from the late 1990s onwards. Analysis of choices and uncertainties in time series show that, depending on choices in time series and parameters, the fraction of statistically significant trends in parts of the ensemble can range from negligible to a complete 100% significance. We also find that, consistent with expectations, the number of statistically significant trends increases with increasing record length.

Although our results indicate that the use multivariate regressions is a valid approach for assessing the state of Antarctic ozone hole recovery, and it can be expected that results will move towards more confidence in recovery with increasing record length, uncertainties in choices currently do not yet support formal identification of recovery of the Antarctic ozone hole.

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Short summary
Recent research suggests the Antarctic ozone hole has started to shrink due to decreasing ozone-depleting substances. Because it could be questioned how robust these results are, we provide an assessment of uncertainties in both the underlying ozone observational records and the detection-attribution method. Although Antarctic ozone concentrations are definitely increasing slowly, the formal identification of recovery is not yet justified, although this will likely become possible this decade.
Final-revised paper