Trends in polar ozone loss since 1989: First signs of recovery in Arctic ozone column
Abstract. Ozone depletion over the polar regions is monitored each year by satellite and ground-based instruments. In this study, the vortex-averaged ozone loss over the last three decades is evaluated for both polar regions using the passive ozone tracer of the chemical transport model TOMCAT/SLIMCAT and total ozone observations from Système d'Analyse par Observation Zénithale (SAOZ) ground-based instruments and Multi-Sensor Reanalysis (MSR2). The passive tracer method allows us to determine the evolution of the daily rate of column ozone destruction, and the magnitude of the cumulative loss at the end of the winter. Three metrics are used to estimate the linear trend since 2000 and to assess the current situation of ozone recovery over both polar regions: 1) The maximum ozone loss at the end of the winter; 2) the onset day of ozone loss at a specific threshold and 3) the ozone loss residuals computed from the differences between annual ozone loss and ozone loss values regressed with respect to sunlit volume of polar stratospheric clouds (VPSC). This latter metric is based on linear and parabolic regressions for ozone loss in the Northern and Southern Hemispheres, respectively. In the Antarctic, metrics 1, and 3, yield trends of -2.3 and -1.8 % dec-1 for the 2000–2021 period, significant at 1 and 2 standard error (σ), respectively. For metric 2, various thresholds were considered, all of them showing a time delay for when they are reached. The trends are significant at the 2σ level and vary from 3.5 to 4.2 day dec-1 between the various thresholds. In the Arctic, metric 1 exhibits large interannual variability and no significant trend is detected; this result is highly influenced by the record ozone losses in 2011 and 2020. Metric 2 is not applied in the Northern Hemisphere due to the difficulty of finding a threshold value in a consistent number of winters. Metric 3 shows a negative trend in Arctic ozone loss residuals of -1.7 ±1 % dec-1, significant at 1σ level. This is therefore the first quantitative detection of ozone recovery in the Arctic springtime lower stratosphere.
Andrea Pazmino et al.
Status: open (until 14 Jul 2023)
- RC1: 'Comment on egusphere-2023-788', Anonymous Referee #1, 04 Jun 2023 reply
Andrea Pazmino et al.
Total O3 columns at polar regions: TOMCAT/SLIMCAT passive and active tracers and merged SAOZ-MSR2 dataset https://doi.org/10.5281/zenodo.7847522
Andrea Pazmino et al.
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This is the first review of the manuscript “Trends in polar ozone loss since 1989: First signs of recovery in Arctic ozone column” submitted by Pazmiño et al. to the EGUsphere journal.
The paper discusses ozone loss rates over the polar regions detected from the SAOZ and MSR2 datasets and uses passive tracer from the TOMCAT/SLIMCAT model to test the indicators of ozone recovery within the polar vortex. Authors utilize three metrics to analyze ozone recovery over the Antarctic and Artic polar regions in the 2000-2021 period. The detection of ozone recovery in the Antarctic vortex is supported by two metrics that indicate negative trends in ozone depletion parameters that are statistically significant. However, in the Arctic, the detection of trends is complicated by large dynamical variability and difficulty to establish threshold value. The first signs of stratospheric ozone recovery (represented as negative residuals with respect to the sunlit volume of the polar stratospheric clouds) in the Northern polar vortex are detected significant at 1 standard deviation error.
This paper is well written and the results of the findings are attributed to the dynamical and chemical processes governing ozone loss in the polar stratosphere. The discussion of large ozone anomalies in the individual years are linked to the SSW and vortex stability. This manuscript has figures that support discussion and conclusion.
I recommend publication of the paper after several questions/comments are answered.
Clarifying qestions and comments.
Line 128. What is the definition of the "overpass" criteria?
Line 143. Please provide station and satellite/model matching criteria. The satellite grid is at 0.5 and SLIMCAT model is at 2.8 degrees. Are there additional matching/averaging is done to reduce sampling biases? Also, it might be useful to provide the number of observations for all stations inside of the vortex during the analyzed period.
Line 149. Please provide additional details of datasets merger, i.e. temporary and special matching, treatment of missing data, weighting of the MSR2 and SAOZ data in the combined record.
Line 163. WHat is the reason for not selecting Match to normalize all years of SAOZ dat? This could make normalization consistent through the entire analysed record.
Line 185. Please clarify what you mean by "diurnal differences".
Line 215-216. Can you please meantion ozone variability in 2019 that was also an anomalous year in the Antarctic ozone depletion? It clearly deviates from other years.
Line 228. Fig. 4 caption. I would not say that 2002/2011 winters are unusual anymore sine we had similar anomalies in recent years. Do you agree?
Lines 325-328. Is there a known reason for the offset between observations and the model since 2003?
Lines 375-377. Please provide uncertainty of the linear and the parabolic fit for the sunlit PSC area and ozone. What does the SLIMCAT data fit show? Do data and a model fit agree? Can you add a plot that shows the change in the sunlit VPSC as function of time? This could provide a reference of climate change over polar regions.
Lines 396-402. If uncertainty of the ozone/PSC fit is taken into account, would the trend of the residuals be significant?
Lines 465, acknowledgements need to be made for the NDACC data
“The data used in this publication were obtained from “NDACC PI name” as part of the Network for the Detection of Atmospheric Composition Change (NDACC) and are available through the NDACC website www.ndacc.org.”
Line 449. Please provide the link to the ERA5 data.