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The study presents a long-term statistical trend analysis of total ozone datasets obtained from various satellites. A multi-variate linear regression wasapplied to annual mean zonal mean data using various natural andanthropogenic explanatory variables that represent dynamical and chemicalprocesses which modify global ozone distributions in a changing climate. Thestudy investigated the magnitude and zonal distribution of the differentatmospheric chemical and dynamical factors contributing to long-term totalozone changes. The regression model included the equivalent effectivestratospheric chlorine (EESC), the 11-year solar cycle, the quasi-biennialoscillation (QBO), stratospheric aerosol loading describing the effects frommajor volcanic eruptions, the El Niño–Southern Oscillation (ENSO), theArctic and Antarctic oscillation (AO/AAO), and accumulated eddy heat flux(EHF), the latter representing changes due to the Brewer–Dobson circulation.The total ozone column data set used here comprises the Solar BackscaterUltraviolet SBUV/SBUV-2 merged ozone data set (MOD) V8.6, the merged data setof the Solar Backscaterr Ultraviolet, the Total Ozone Mapping Spectrometerand the Ozone Monitoring Instrument SBUV/TOMS/OMI (1979–2012) MODV8.0 and the merged data set of the Global Ozone Monitoring Experiment,the Scanning Imaging Absorption spectroMeter for Atmospheric ChartograpHY andthe Global Ozone Monitoring Experiment 2 GOME/SCIAMACHY/GOME-2 (GSG)(1995–2012). The trend analysis was performed for twenty-six 5° widelatitude bands from 65° S to 65° N, and the analysisexplained most of the ozone variability to within 70 to 90%. The resultsshow that QBO dominates the ozone variability in the tropics (±7 DU)while at higher latitudes, the dynamical indices, AO/AAO and eddy heat flux,have substantial influence on total ozone variations by up to ±10 DU.The contribution from volcanic aerosols is only prominent during the majoreruption periods (El Chichón and Mt. Pinatubo), and together with theENSO signal, is more evident in the Northern Hemisphere. The signature of thesolar cycle covers all latitudes and contributes about 10 DU from solarmaximum to solar minimum. EESC is found to be a main contributor to thelong-term ozone decline and the trend changes after the end of the 1990s.From the EESC fits, statistically significant upward trends after 1997 werefound in the extratropics, which points at the slowing of ozone decline andthe onset of ozone recovery. The EESC based trends are compared with thetrends obtained from the statistical piecewise linear trend (PWLT)  model(known as hockey stick) with a turnaround in 1997 to examine the differencesbetween both approaches. In case of the SBUV merged V8.6 data the EESC andPWLT trends before and after 1997 are in good agreement (within 2 σ),however, the positive post-1997 linear trends from the PWLT regression arenot significant within 2 σ.  A sensitivity study is carried out by comparing the regression results, usingSBUV/SBUV-2 MOD V8.6 merged time series (1979–2012) and a merged data setcombining SBUV/SBUV-2 (1979–June 1995) and GOME/SCIAMACHY/GOME-2 ("GSG")WFDOAS (Weighting Function DOAS) (July 1995–2012) as well as SBUV/TOMS/OMIMOD V8.0 (1979–2012) in the regression analysis in order to investigate theuncertainty in the long-term trends due to different ozone data sets and dataversions. Replacing the late SBUV/SBUV-2 merged data record with GSG data(unscaled and adjusted) leads to very similar results demonstrating the highconsistency between satellite data sets. However, the comparison of the newSBUV/SBUV-2 MOD V8.6 with the MOD V8.0 and MOD8.6/GSG data showed somewhatsmaller sensitivities with regard to several proxies as well as the linearEESC trends. On the other hand, the PWLT trends after 1997 show somedifferences, however, within the 2 σ error bars the PWLT trends agreewith each other for all three data sets

Total ozone trends and variability during 1979–2012 from merged data sets of various satellites