scholarly journals Merging of ozone profiles from SCIAMACHY, OMPS and SAGE II observations to study stratospheric ozone changes

2019 ◽  
Vol 12 (4) ◽  
pp. 2423-2444
Author(s):  
Carlo Arosio ◽  
Alexei Rozanov ◽  
Elizaveta Malinina ◽  
Mark Weber ◽  
John P. Burrows
Keyword(s):  
Time Series ◽  
Stratospheric Ozone ◽  
Multivariate Regression Analysis ◽  
Stratospheric Aerosol ◽  
Montreal Protocol ◽  
Inversion Algorithm ◽  
Data Set ◽  
Large Variability ◽  
Stratospheric Temperature

Abstract. This paper presents vertically and zonally resolved merged ozone time series from limb measurements of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and the Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (LP). In addition, we present the merging of the latter two data sets with zonally averaged profiles from Stratospheric Aerosol and Gas Experiment (SAGE) II. The retrieval of ozone profiles from SCIAMACHY and OMPS-LP is performed using an inversion algorithm developed at the University of Bremen. To optimize the merging of these two time series, we use data from the Microwave Limb Sounder (MLS) as a transfer function and we follow two approaches: (1) a conventional method involving the calculation of deseasonalized anomalies and (2) a “plain-debiasing” approach, generally not considered in previous similar studies, which preserves the seasonal cycles of each instrument. We find a good correlation and no significant drifts between the merged and MLS time series. Using the merged data set from both approaches, we apply a multivariate regression analysis to study ozone changes in the 20–50 km range over the 2003–2018 period. Exploiting the dense horizontal sampling of the instruments, we investigate not only the zonally averaged field, but also the longitudinally resolved long-term ozone variations, finding an unexpected and large variability, especially at mid and high latitudes, with variations of up to 3 %–5 % per decade at altitudes around 40 km. Significant positive linear trends of about 2 %–4 % per decade were identified in the upper stratosphere between altitudes of 38 and 45 km at mid latitudes. This is in agreement with the predicted recovery of upper stratospheric ozone, which is attributed to both the adoption of measures to limit the release of halogen-containing ozone-depleting substances (Montreal Protocol) and the decrease in stratospheric temperature resulting from the increasing concentration of greenhouse gases. In the tropical stratosphere below 25 km negative but non-significant trends were found. We compare our results with previous studies and with short-term trends calculated over the SCIAMACHY period (2002–2012). While generally a good agreement is found, some discrepancies are seen in the tropical mid stratosphere. Regarding the merging of SAGE II with SCIAMACHY and OMPS-LP, zonal mean anomalies are taken into consideration and ozone trends before and after 1997 are calculated. Negative trends above 30 km are found for the 1985–1997 period, with a peak of −6 % per decade at mid latitudes, in agreement with previous studies. The increase in ozone concentration in the upper stratosphere is confirmed over the 1998–2018 period. Trends in the tropical stratosphere at 30–35 km show an interesting behavior: over the 1998–2018 period a negligible trend is found. However, between 2004 and 2011 a negative long-term change is detected followed by a positive change between 2012 and 2018. We attribute this behavior to dynamical changes in the tropical middle stratosphere.

scholarly journals Merging of ozone profiles from SCIAMACHY, OMPS and SAGE II observations to study stratospheric ozone changes

2018 ◽  
Author(s):  
Carlo Arosio ◽  
Alexei Rozanov ◽  
Elizaveta Malinina ◽  
Mark Weber ◽  
John P. Burrows
Keyword(s):  
Time Series ◽  
Stratospheric Ozone ◽  
Multivariate Regression Analysis ◽  
Stratospheric Aerosol ◽  
Montreal Protocol ◽  
Data Sets ◽  
Data Set ◽  
Vertical Range ◽  
Scanning Imaging ◽  
Ozone Depleting Substances

Abstract. This paper presents vertically and zonally resolved merged ozone time series from limb measurements of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and the Ozone Mapping and Profiler Suite (OMPS). In addition, we present the merging of the latter two data sets with zonally averaged profiles from the Stratospheric Aerosol and Gas Experiment (SAGE) II. The retrieval of ozone profiles from SCIAMACHY and OMPS is performed at the University of Bremen. Within the merging procedure of these two time series we use data from the Microwave Limb Sounder (MLS) as a transfer function and we follow two approaches: (1) a standard method involving the calculation of deseasonalized anomalies and (2) a plain-debiasing approach, generally not considered in previous similar studies, which preserves the seasonal cycles of each instrument. We find a good correlation and no significant drifts between the merged and MLS time series. Using the merged data set, we apply a multivariate regression analysis to study ozone changes over the 2003–2018 period in the 20–50 km vertical range. Exploiting the high horizontal sampling of the instruments, we investigate not only the zonally averaged field but also the longitudinally resolved long-term ozone variations, finding a remarkable variability, especially at mid- and high-latitudes. Significant positive linear trends of about 2–4 % per decade were identified in the upper stratosphere between 38 and 45 km at mid-latitudes. This is in agreement with the predicted recovery of upper stratospheric ozone, which is attributed both to the adoption of measures to limit the release of halogen-containing ozone-depleting substances included in the Montreal protocol and to the increasing concentration of greenhouse gases. In the tropical stratosphere below 25 km negative but non-significant trends were found. We compare our results with similar previous studies and with short-term trends calculated over the SCIAMACHY period: while a general agreement is found, some discrepancies are seen in the tropical mid-stratosphere. Regarding the merging of SAGE II with SCIAMACHY and OMPS, zonal mean anomalies are taken into consideration and ozone trends after and before 1997 are shown. Negative trends above 30 km are found for the 1985–1997 period, with a peak of −6 % per decade at mid-latitudes, in agreement with previous studies. The increase of ozone concentration in the upper stratosphere is confirmed considering the 1998–2018 period. Trends in the middle and lower tropical stratosphere are found to be non-significant.

scholarly journals Estimates of European emissions of methyl chloroform using a Bayesian inversion method

2014 ◽  
Vol 14 (18) ◽  
pp. 9755-9770 ◽  
Author(s):  
M. Maione ◽  
F. Graziosi ◽  
J. Arduini ◽  
F. Furlani ◽  
U. Giostra ◽  
...  
Keyword(s):  
Point Source ◽  
High Frequency ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Source Analysis ◽  
Bayesian Inversion ◽  
Inversion Method ◽  
Data Set ◽  
Methyl Chloroform

Abstract. Methyl chloroform (MCF) is a man-made chlorinated solvent contributing to the destruction of stratospheric ozone and is controlled under the "Montreal Protocol on Substances that Deplete the Ozone Layer" and its amendments, which called for its phase-out in 1996 in developed countries and 2015 in developing countries. Long-term, high-frequency observations of MCF carried out at three European sites show a constant decline in the background mixing ratios of MCF. However, we observe persistent non-negligible mixing ratio enhancements of MCF in pollution episodes, suggesting unexpectedly high ongoing emissions in Europe. In order to identify the source regions and to give an estimate of the magnitude of such emissions, we have used a Bayesian inversion method and a point source analysis, based on high-frequency long-term observations at the three European sites. The inversion identified southeastern France (SEF) as a region with enhanced MCF emissions. This estimate was confirmed by the point source analysis. We performed this analysis using an 11-year data set, from January 2002 to December 2012. Overall, emissions estimated for the European study domain decreased nearly exponentially from 1.1 Gg yr−1 in 2002 to 0.32 Gg yr−1 in 2012, of which the estimated emissions from the SEF region accounted for 0.49 Gg yr−1 in 2002 and 0.20 Gg yr−1 in 2012. The European estimates are a significant fraction of the total semi-hemisphere (30–90° N) emissions, contributing a minimum of 9.8% in 2004 and a maximum of 33.7% in 2011, of which on average 50% are from the SEF region. On the global scale, the SEF region is thus responsible for a minimum of 2.6% (in 2003) and a maximum of 10.3% (in 2009) of the global MCF emissions.

scholarly journals Stratospheric ozone trends for 1985–2018: sensitivity to recent large variability

2019 ◽  
Author(s):  
William T. Ball ◽  
Justin Alsing ◽  
Johannes Staehelin ◽  
Sean M. Davis ◽  
Lucien Froidevaux ◽  
...  
Keyword(s):  
Seasonal Variability ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Regression Analyses ◽  
Large Variability ◽  
Ozone Trends ◽  
Ozone Depleting Substances ◽  
Made In

Abstract. The Montreal Protocol has successfully prevented catastrophic losses of stratospheric ozone, and signs of recovery are now evident. Nevertheless, recent work suggests that ozone in the lower stratosphere ( 95 %, 30° S–30° N) decreases dominate the quasi-global integrated decrease (99 % probability); the integrated tropical stratospheric column (1–100 hPa, 30° S–30° N) displays a significant overall decrease, with 95 % probability. These decreases do not reveal an inefficacy of the Montreal Protocol. Rather, they suggest other effects to be at work, mainly dynamical variability on long or short timescale, counteracting the protocol's regulation of halogenated ozone depleting substances (hODS). We demonstrate that large inter-annual mid-latitude variations (30° –60° ), such as the 2017 resurgence, are driven by non-linear QBO phase-dependent seasonal variability. However, this variability is not represented in current regression analyses. To understand if observed lower stratospheric decreases are a transient or long-term phenomenon, progress needs to be made in accounting for this dynamically-driven variability.

scholarly journals Estimates of European emissions of methyl chloroform using a Bayesian inversion method

2014 ◽  
Vol 14 (6) ◽  
pp. 8209-8256 ◽  
Author(s):  
M. Maione ◽  
F. Graziosi ◽  
J. Arduini ◽  
F. Furlani ◽  
U. Giostra ◽  
...  
Keyword(s):  
Point Source ◽  
High Frequency ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Source Analysis ◽  
Bayesian Inversion ◽  
Inversion Method ◽  
Data Set ◽  
Methyl Chloroform

Abstract. Methyl chloroform (MCF) is a man-made chlorinated solvent contributing to the destruction of stratospheric ozone and is controlled under the Montreal Protocol on Substances that Deplete the Ozone Layer. Long-term, high-frequency observations of MCF carried out at three European sites show a constant decline of the background mixing ratios of MCF. However, we observe persistent non-negligible mixing ratio enhancements of MCF in pollution episodes suggesting unexpectedly high ongoing emissions in Europe. In order to identify the source regions and to give an estimate of the magnitude of such emissions, we have used a Bayesian inversion method and a point source analysis, based on high-frequency long-term observations at the three European sites. The inversion identified south-eastern France (SEF) as a region with enhanced MCF emissions. This estimate was confirmed by the point source analysis. We performed this analysis using an eleven-year data set, from January 2002 to December 2012. Overall emissions estimated for the European study domain decreased nearly exponentially from 1.1 Gg yr−1 in 2002 to 0.32 Gg yr−1 in 2012, of which the estimated emissions from the SEF region accounted for 0.49 Gg yr−1 in 2002 and 0.20 Gg yr−1 in 2012. The European estimates are a significant fraction of the total semi-hemisphere (30–90° N) emissions, contributing a minimum of 9.8% in 2004 and a maximum of 33.7% in 2011, of which on average 50% are from the SEF region. On the global scale, the SEF region is thus responsible from a minimum of 2.6% (in 2003) to a maximum of 10.3% (in 2009) of the global MCF emissions.

scholarly journals Coherence of long-term stratospheric ozone vertical distribution time series used for the study of ozone recovery at a northern mid-latitude station

2011 ◽  
Vol 11 (10) ◽  
pp. 4957-4975 ◽  
Author(s):  
P. J. Nair ◽  
S. Godin-Beekmann ◽  
A. Pazmiño ◽  
A. Hauchecorne ◽  
G. Ancellet ◽  
...  
Keyword(s):  
Time Series ◽  
Stratospheric Ozone ◽  
Stratospheric Aerosol ◽  
Data Sets ◽  
Zero Bias ◽  
Lidar Measurements ◽  
Relative Differences ◽  
Difference Time

Abstract. The coherence of stratospheric ozone time series retrieved from various observational records is investigated at Haute-Provence Observatory (OHP–43.93° N, 5.71° E). The analysis is accomplished through the intercomparison of collocated ozone measurements of Light Detection and Ranging (lidar) with Solar Backscatter UltraViolet(/2) (SBUV(/2)), Stratospheric Aerosol and Gas Experiment II (SAGE~II), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS) on Upper Atmosphere Research Satellite (UARS) and Aura and Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite observations as well as with in situ ozonesondes and ground-based Umkehr measurements performed at OHP. A detailed statistical study of the relative differences of ozone observations over the whole stratosphere is performed to detect any specific drift in the data. On average, all instruments show their best agreement with lidar at 20–40 km, where deviations are within ±5 %. Discrepancies are somewhat higher below 20 and above 40 km. The agreement with SAGE II data is remarkable since average differences are within ±1 % at 17–41 km. In contrast, Umkehr data underestimate systematically the lidar measurements in the whole stratosphere with a near zero bias at 16–8 hPa (~30 km). Drifts are estimated using simple linear regression for the data sets analysed in this study, from the monthly averaged difference time series. The derived values are less than ±0.5 % yr−1 in the 20–40 km altitude range and most drifts are not significant at the 2σ level. We also discuss the possibilities of extending the SAGE II and HALOE data with the GOMOS and Aura MLS data in consideration with relative offsets and drifts since the combination of such data sets are likely to be used for the study of stratospheric ozone recovery in the future.

scholarly journals Evolution of stratospheric ozone and water vapour time series studied with satellite measurements

2009 ◽  
Vol 9 (1) ◽  
pp. 1157-1209 ◽  
Author(s):  
A. Jones ◽  
J. Urban ◽  
D. P. Murtagh ◽  
P. Eriksson ◽  
S. Brohede ◽  
...  
Keyword(s):  
Time Series ◽  
Water Vapour ◽  
Stratospheric Ozone ◽  
Stratospheric Aerosol ◽  
Data Sets ◽  
Quasi Biennial Oscillation ◽  
Long Term Stability ◽  
Infrared Imager ◽  
Scanning Imaging

Abstract. The long term evolution of stratospheric ozone and water vapour has been investigated by extending satellite time series to April 2008. For ozone, we examine monthly average ozone values from various satellite data sets for nine latitude and altitude bins covering 60° S to 60° N and 20–45 km and covering the time period 1979–2008. Data are from the Stratospheric Aerosol and Gas Experiment (SAGE I+II), the HALogen Occultation Experiment (HALOE), the Solar BackscatterUltraViolet-2 (SBUV/2) instrument, the Sub-Millimetre Radiometer (SMR), the Optical Spectrograph InfraRed Imager System (OSIRIS), and the SCanning Imaging Absorption spectroMeter for Atmospheric CHartograpY (SCIAMACHY). Monthly ozone anomalies are calculated by utilising a linear regression model, which also models the solar, quasi-biennial oscillation (QBO), and seasonal cycle contributions. Individual instrument ozone anomalies are combined producing a weighted all instrument average. Assuming a turning point of 1997 and that the all instrument average is represented by good instrumental long term stability, the largest statistically significant ozone declines from 1979–1997 are seen at the mid-latitudes between 35 and 45 km, namely −7.7%/decade in the Northern Hemisphere and −7.8%/decade in the Southern Hemisphere. For the period 1997 to 2008 we find that the southern mid-latitudes between 35 and 45 km show the largest ozone recovery (+3.4%/decade) compared to other global regions, although the estimated trend model error is of a similar magnitude (+2.1%/decade, at the 95% confidence level). An all instrument average is also constructed from water vapour anomalies during 1984–2008, using the SAGE II, HALOE, SMR, and the Microwave Limb Sounder (aura/MLS) measurements. We report that the decrease in water vapour values after 2001 slows down around 2004 in the lower tropical stratosphere (20–25 km), and has even shown signs of increasing values in upper stratospheric mid-latitudes. We show that a similar correlation is also seen with the temperature measured at 100 hPa during this same period.

scholarly journals Evolution of stratospheric ozone and water vapour time series studied with satellite measurements

2009 ◽  
Vol 9 (16) ◽  
pp. 6055-6075 ◽  
Author(s):  
A. Jones ◽  
J. Urban ◽  
D. P. Murtagh ◽  
P. Eriksson ◽  
S. Brohede ◽  
...  
Keyword(s):  
Time Series ◽  
Water Vapour ◽  
Stratospheric Ozone ◽  
Stratospheric Aerosol ◽  
Data Sets ◽  
Model Errors ◽  
Quasi Biennial Oscillation ◽  
Sigma Level ◽  
Scanning Imaging

Abstract. The long term evolution of stratospheric ozone and water vapour has been investigated by extending satellite time series to April 2008. For ozone, we examine monthly average ozone values from various satellite data sets for nine latitude and altitude bins covering 60° S to 60° N and 20–45 km and covering the time period of 1979–2008. Data are from the Stratospheric Aerosol and Gas Experiment (SAGE I+II), the HALogen Occultation Experiment (HALOE), the Solar BackscatterUltraViolet-2 (SBUV/2) instrument, the Sub-Millimetre Radiometer (SMR), the Optical Spectrograph InfraRed Imager System (OSIRIS), and the SCanning Imaging Absorption spectroMeter for Atmospheric CHartograpY (SCIAMACHY). Monthly ozone anomalies are calculated by utilising a linear regression model, which also models the solar, quasi-biennial oscillation (QBO), and seasonal cycle contributions. Individual instrument ozone anomalies are combined producing an all instrument average. Assuming a turning point of 1997 and that the all instrument average is represented by good instrumental long term stability, the largest statistically significant ozone declines (at two sigma) from 1979–1997 are seen at the mid-latitudes between 35 and 45 km, namely −7.2%±0.9%/decade in the Northern Hemisphere and −7.1%±0.9%/in the Southern Hemisphere. Furthermore, for the period 1997 to 2008 we find that the same locations show the largest ozone recovery (+1.4% and +0.8%/decade respectively) compared to other global regions, although the estimated trend model errors indicate that the trend estimates are not significantly different from a zero trend at the 2 sigma level. An all instrument average is also constructed from water vapour anomalies during 1991–2008, using the SAGE II, HALOE, SMR, and the Microwave Limb Sounder (Aura/MLS) measurements. We report that the decrease in water vapour values after 2001 slows down around 2004–2005 in the lower tropical stratosphere (20–25 km) and has even shown signs of increasing until present. We show that a similar correlation is also seen with the temperature measured at 100 hPa during this same period.

scholarly journals Coherence of long-term stratospheric ozone vertical distribution time series used for the study of ozone recovery at a northern mid-latitude station

2010 ◽  
Vol 10 (11) ◽  
pp. 28519-28564
Author(s):  
P. J. Nair ◽  
S. Godin-Beekmann ◽  
A. Pazmiño ◽  
A. Hauchecorne ◽  
G. Ancellet ◽  
...  
Keyword(s):  
Time Series ◽  
Stratospheric Ozone ◽  
Stratospheric Aerosol ◽  
Data Sets ◽  
Zero Bias ◽  
Lidar Measurements ◽  
Relative Differences ◽  
Difference Time

Abstract. The coherence of stratospheric ozone time series retrieved from various observational records is investigated at Haute–Provence Observatory (OHP–43.93° N, 5.71° E). The analysis is accomplished through the intercomparison of collocated ozone measurements of Light Detection and Ranging (lidar) with Solar Backscatter UltraViolet(/2) (SBUV(/2)), Stratospheric Aerosol and Gas Experiment II (SAGE II), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS) on Upper Atmosphere Research Satellite (UARS) and Aura and Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite observations as well as with in-situ ozonesondes and ground-based Umkehr measurements performed at OHP. A detailed statistical study of the relative differences of ozone observations is performed to detect any specific drifts in the data. On average, all instruments show their best agreement with lidar at 20–40 km, where deviations are within ±5%. Discrepancies are somewhat higher below 20 and above 40 km. The agreement with SAGE II data is remarkable since average differences are within ±1% at 17–41 km. In contrast, Umkehr data underestimate systematically the lidar measurements in the whole stratosphere albeit a near zero bias is observed at 16–8 hPa (~30 km). Drifts are estimated using simple linear regression for the long-term (more than 10 years long) data sets analysed in this study, from the monthly averaged difference time series. The derived values are less than ±0.5% yr−1 in the 20–40 km altitude range and most drifts are not significant at the 2σ level.

scholarly journals A re-evaluated Canadian ozonesonde record: measurements of the vertical distribution of ozone over Canada from 1966 to 2013

2016 ◽  
Vol 9 (1) ◽  
pp. 195-214 ◽  
Author(s):  
D. W. Tarasick ◽  
J. Davies ◽  
H. G. J. Smit ◽  
S. J. Oltmans
Keyword(s):  
Time Series ◽  
Stratospheric Ozone ◽  
The Arctic ◽  
Recent Period ◽  
Data Set ◽  
Design Changes ◽  
Resolute Bay ◽  
The Vertical Distribution ◽  
Homogeneous Data

Abstract. In Canada routine ozone soundings have been carried at Resolute Bay since 1966, making this record the longest in the world. Similar measurements started in the 1970s at three other sites, and the network was expanded in stages to 10 sites by 2003. This important record for understanding long-term changes in tropospheric and stratospheric ozone has been re-evaluated as part of the SPARC/IO3C/IGACO-O3/NDACC (SI2N) initiative. The Brewer–Mast sonde, used in the Canadian network until 1980, is different in construction from the electrochemical concentration cell (ECC) sonde, and the ECC sonde itself has also undergone a variety of minor design changes over the period 1980–2013. Corrections have been made for the estimated effects of these changes to produce a more homogeneous data set. The effect of the corrections is generally modest. However, the overall result is entirely positive: the comparison with co-located total ozone spectrometers is improved, in terms of both bias and standard deviation, and trends in the bias have been reduced or eliminated. An uncertainty analysis (including the additional uncertainty from the corrections, where appropriate) has also been conducted, and the altitude-dependent estimated uncertainty is included with each revised profile. The resulting time series show negative trends in the lower stratosphere of up to 5 % decade−1 for the period 1966–2013. Most of this decline occurred before 1997, and linear trends for the more recent period are generally not significant. The time series also show large variations from year to year. Some of these anomalies can be related to cold winters (in the Arctic stratosphere) or changes in the Brewer–Dobson circulation, which may thereby be influencing trends. In the troposphere, trends for the 48-year period are small and for the most part not significant. This suggests that ozone levels in the free troposphere over Canada have not changed significantly in nearly 50 years.

scholarly journals Stratospheric ozone trends for 1985–2018: sensitivity to recent large variability

2019 ◽  
Vol 19 (19) ◽  
pp. 12731-12748 ◽  
Author(s):  
William T. Ball ◽  
Justin Alsing ◽  
Johannes Staehelin ◽  
Sean M. Davis ◽  
Lucien Froidevaux ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Quasi Biennial Oscillation ◽  
Total Column Ozone ◽  
Large Variability ◽  
Positive Effects ◽  
Ozone Trends

Abstract. The Montreal Protocol, and its subsequent amendments, has successfully prevented catastrophic losses of stratospheric ozone, and signs of recovery are now evident. Nevertheless, recent work has suggested that ozone in the lower stratosphere (< 24 km) continued to decline over the 1998–2016 period, offsetting recovery at higher altitudes and preventing a statistically significant increase in quasi-global (60∘ S–60∘ N) total column ozone. In 2017, a large lower stratospheric ozone resurgence over less than 12 months was estimated (using a chemistry transport model; CTM) to have offset the long-term decline in the quasi-global integrated lower stratospheric ozone column. Here, we extend the analysis of space-based ozone observations to December 2018 using the BASICSG ozone composite. We find that the observed 2017 resurgence was only around half that modelled by the CTM, was of comparable magnitude to other strong interannual changes in the past, and was restricted to Southern Hemisphere (SH) midlatitudes (60–30∘ S). In the SH midlatitude lower stratosphere, the data suggest that by the end of 2018 ozone is still likely lower than in 1998 (probability ∼80 %). In contrast, tropical and Northern Hemisphere (NH) ozone continue to display ongoing decreases, exceeding 90 % probability. Robust tropical (>95 %, 30∘ S–30∘ N) decreases dominate the quasi-global integrated decrease (99 % probability); the integrated tropical stratospheric column (1–100 hPa, 30∘ S–30∘ N) displays a significant overall ozone decrease, with 95 % probability. These decreases do not reveal an inefficacy of the Montreal Protocol; rather, they suggest that other effects are at work, mainly dynamical variability on long or short timescales, counteracting the positive effects of the Montreal Protocol on stratospheric ozone recovery. We demonstrate that large interannual midlatitude (30–60∘) variations, such as the 2017 resurgence, are driven by non-linear quasi-biennial oscillation (QBO) phase-dependent seasonal variability. However, this variability is not represented in current regression analyses. To understand if observed lower stratospheric ozone decreases are a transient or long-term phenomenon, progress needs to be made in accounting for this dynamically driven variability.

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