the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 May 2023
Total ozone variability and trends over the South Pole during the wintertime
Abstract. The Antarctic polar vortex creates unique chemical and dynamical conditions when the stratospheric air over Antarctica is isolated from the rest of the stratosphere. As a result, stratospheric ozone within the vortex remains largely unchanged for a five-month period from April until late August when the sunrise and extremely cold temperatures create favorable conditions for rapid ozone loss. Such prolonged stable conditions within the vortex make it possible to estimate the total ozone levels there from sparse wintertime ozone observations at the South Pole. The available records of focused Moon (FM) observations by Dobson and Brewer spectrophotometers at the Amundsen-Scott South Pole Station (for the periods 1964–2022 and 2008–2022, respectively) as well as integrated ozonesonde profiles (1986–2022) and MERRA-2 reanalysis data (1980–2022) were used to estimate the total ozone variability and long-term changes over the South Pole. Comparisons with MERRA-2 reanalysis data for the period 1980–2022 demonstrated that the uncertainties of Dobson and Brewer daily mean FM values are about 2.5 %–4 %. Wintertime (April–August) MERRA-2 data have a bias with Dobson data of -8.5 % in 1980–2004 and 1.5 % in 2005–2022. The mean difference between wintertime Dobson and Brewer data in 2008–2022 was about 1.6 %; however, this difference can be largely explained by various systematic errors in Brewer data. The wintertime ozone values over the South Pole during the last 20 years were about 12 % below the pre-1980s level, i.e., the decline there was nearly twice larger than that over southern midlatitudes. It is probably the largest long-term ozone decline aside from the springtime Antarctic ozone depletion. While wintertime ozone decline over the pole has hardly any impact on the environment, it can be used as an indicator to diagnose the state of the ozone layer, particularly because it requires data from only one station. Dobson and ozonesonde data after 2001 show a small positive, but not statistically significant, trend in ozone values of about 1.5% per decade that is in line with the trend expected from the concentration of the ozone depleting substances in the stratosphere.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-773', Anonymous Referee #1, 14 Jun 2023
Review of the manuscript with the title "Total ozone variability and trends over the South Pole during the
wintertime" by Fioletov et al.The manuscript studies total ozone measurements at the South Pole during winter time. Dobson, Brewer, ozone soundings and MERRA-2 data are used. The study includes quality assurance of the data as well as uncertainty estimates. This is the first time the analysis is done for such a long period in the winter time, as previous studies are more focused on springtime Antarctic ozone loss. The study brings new information on total ozone trends in the Southern polar area and adds valuable information to global ozone trends at those latitudes. The manuscript is well-written and includes appropriate references. The authors should address the general comments and the more specific comments before publication of the manuscript.
General Comments:
My main concern is related to the correction of MERRA-2 data which is based on only one correction factor over the whole winter when analysing the MERRA-2 SBUV period. Why not use a correction factor per month, as suggested by the Figure 3? Please see also the specific comments. The second concern is the use of the EESC fit. For a reader not familiar with the methodology the text is rather confusing. This needs to be clarified.
Specific Comments:Page 2, Line 5: Polar vortex breakdown time: November-December?
Page 2, Line 22: total ozone declining trend: for which time period? Yearly mean?
Page 3, Line 28: Please specify how the temperature and ozone profiles are used in the retrieval algorithm.
Page 4, Line 8 and page 5, line 4: Until which period you can still measure good DS measurements? In the winter, with no Sun, I suppose it is impossible.
Page 4, Line 9: How do you make the choice of the representative daily value?
Page 4, line 30. I don't think Kerr et al. 2010 is a "recent" paper ....13 years old. Maybe better to delete "recent". Please add some sentences on the calibration and harmonization of the Brewer including used corrections to the data, like the use of sl-lamp measurements.
Page 6, line 4: For MERRA-2 during the polar night: is the total ozone for the South Pole actually the total ozone at latitude 82 degrees South? Or is it extrapolated somehow from that latitude to the South Pole? Please specify.
Page 6, line 14: "...existence of some systematic seasonal biases..." Does this include any information about the winter (the season you studied)? If yes, please add it to the paragraph.
Page 7, line 1: "This could be related to some horizontal inhomogeneity of the ozone distribution over the pole that led to variations in measured ozone due to changing lunar azimuth angle." I can't follow the sentence. Please clarify. Are the changes real or an artifact caused by changing lunar azimuth angle?
Page 7, line 31: "There was also a 3% difference..." Was it the mean difference? Please specify.
Page 7 + Figure 3: Correction of MERRA-2 data for 1980-2004. Why didn't you use monthly mean differences for the correction in April-August? There seems to be a clear month-dependent difference. You can still see a month-dependent difference in the corrected data ranging from -5% to 5%.
Page 9, line 25: "The estimated ozone variability is relatively low, about 15 DU for daily averages and 10 DU for monthly
values or about 6% and 4%, respectively." -> Do you mean over the winter period April-August? Please specify.Page 11, Section 4.2. For a reader not familiar with EESC fit it is very difficult to understand what is fitted to what. You should describe the methodology in more detail, and how did you end up with the fit in the right columns of Fig. 7.
page 14, line 10: "A decline in ozone due to gas-phase ozone destruction from ODSs is probably the largest since the time for an
air parcel to travel from the tropics to high latitudes is the longest." -> Please open this statement. Is this related to the Brewer-Dobson circulation transporting ozone from the tropics to the pole? Does ODS deplete it the whole way? During which months?Citation: https://doi.org/10.5194/egusphere-2023-773-RC1 -
AC1: 'Reply on RC1', Vitali Fioletov, 21 Jul 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-773/egusphere-2023-773-AC1-supplement.pdf
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AC1: 'Reply on RC1', Vitali Fioletov, 21 Jul 2023
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RC2: 'very nice paper, only rather minor comments', Mark Weber, 12 Jul 2023
This paper reports on ozone changes observed since the 1960s at the
Amundsen-Scott South Pole Station (SPO). A particular focus lies in
the winter months just before the period of rapid ozone depletion in
spring ("ozone hole period"). This time of the year is covered by full
moon (FM) measurements by Brewer and Dobson spectrophotometers
complemented by regular ozone sondes and MERRA2 reanalysis data.
Regular direct sun (DS) measurements by Brewer and Dobsons are also
used to contrast the ozone changes in the winter months to other
seasons and latitudes. Wintertime ozone declined by about 12% from the
pre-1980s until the late 1990s, a larger change than observed at lower
latitudes and in other sesaons, except for the ozone hole period.The paper is well written and results are well presented. After
adressing some rather minor issues as outlined below, the paper will
be well suited for publication in ACP.p. 6, l. 15ff: A great part of the paper deals with the adjustments of
the various datasets. As a reference for adjusting all data types the
long-term Dobson data is used (p. 7, l. 14). For justification only the
study by Bernhard et al. (2005) is cited. I think a few more sentences
are here needed to explain why the Dobson record is most suitable as a
refence dataset here.p. 7, l. 32: "... remove that bias for some of the plots". So the
corrections are only applied in the plots but not for the data. I find
this a bit awkward, why not say simply the data has been corrected,
which would be important if the adjusted data im made publicly
available (see my later comments on Data Availability)p. 8, l. 5: I think that the bottom panel is not showing what is
described in the main text and figure caption. MERRA2 data are the
same as in the top panel, but all other data have been adjusted (not
the other way around).p. 11, l. 5: "four seasons" --> "three seasons"
p. 11., l. 25: not clear what is meant with "analysis of the
residuals". Please specify. A fit of only the EESC curve to the data
will result in large residuals as the short-term variability is not
fitted. Maybe it would be good to show some plots of residuals to make
the point here (could be put in the appendix).Fig. 8 (and other plots): Light blue color lines are dificult to
distinguish, in particular with different line styles. The light blue
color is not a particular good color for color blind people. I
strongly suggest to use a different color. This applies also for the
other plots using the same color.p. 14, l. 7: "Rapid ozone destruction on polar stratospheric clouds in
the springtime Antarctic vortex affects ozone levels in subsequent
months everywhere in the southern hemisphere, but its impact on the
polar ozone should be at least as strong as anywhere else." I find
this sentence a bit awkward. I think what was meant to be said is that
the polar ozone loss (ozone ozone hole) is not affecting the
wintertime ozone, so that gas-phase chemistry is only relevant in
winter. Apart from ODS gas-phase chmistry some dynamic contributions can
not be ruled out as suggested in the main text. I think this should be
mentiond here as well.p. 14, l. 17: The data at SPO, in particular the adjusted data
should be made available publicly for tracability.p. 34, l. 4: "in increasing" --> "is increasing"
Citation: https://doi.org/10.5194/egusphere-2023-773-RC2 -
AC2: 'Reply on RC2', Vitali Fioletov, 21 Jul 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-773/egusphere-2023-773-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Vitali Fioletov, 21 Jul 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-773', Anonymous Referee #1, 14 Jun 2023
Review of the manuscript with the title "Total ozone variability and trends over the South Pole during the
wintertime" by Fioletov et al.The manuscript studies total ozone measurements at the South Pole during winter time. Dobson, Brewer, ozone soundings and MERRA-2 data are used. The study includes quality assurance of the data as well as uncertainty estimates. This is the first time the analysis is done for such a long period in the winter time, as previous studies are more focused on springtime Antarctic ozone loss. The study brings new information on total ozone trends in the Southern polar area and adds valuable information to global ozone trends at those latitudes. The manuscript is well-written and includes appropriate references. The authors should address the general comments and the more specific comments before publication of the manuscript.
General Comments:
My main concern is related to the correction of MERRA-2 data which is based on only one correction factor over the whole winter when analysing the MERRA-2 SBUV period. Why not use a correction factor per month, as suggested by the Figure 3? Please see also the specific comments. The second concern is the use of the EESC fit. For a reader not familiar with the methodology the text is rather confusing. This needs to be clarified.
Specific Comments:Page 2, Line 5: Polar vortex breakdown time: November-December?
Page 2, Line 22: total ozone declining trend: for which time period? Yearly mean?
Page 3, Line 28: Please specify how the temperature and ozone profiles are used in the retrieval algorithm.
Page 4, Line 8 and page 5, line 4: Until which period you can still measure good DS measurements? In the winter, with no Sun, I suppose it is impossible.
Page 4, Line 9: How do you make the choice of the representative daily value?
Page 4, line 30. I don't think Kerr et al. 2010 is a "recent" paper ....13 years old. Maybe better to delete "recent". Please add some sentences on the calibration and harmonization of the Brewer including used corrections to the data, like the use of sl-lamp measurements.
Page 6, line 4: For MERRA-2 during the polar night: is the total ozone for the South Pole actually the total ozone at latitude 82 degrees South? Or is it extrapolated somehow from that latitude to the South Pole? Please specify.
Page 6, line 14: "...existence of some systematic seasonal biases..." Does this include any information about the winter (the season you studied)? If yes, please add it to the paragraph.
Page 7, line 1: "This could be related to some horizontal inhomogeneity of the ozone distribution over the pole that led to variations in measured ozone due to changing lunar azimuth angle." I can't follow the sentence. Please clarify. Are the changes real or an artifact caused by changing lunar azimuth angle?
Page 7, line 31: "There was also a 3% difference..." Was it the mean difference? Please specify.
Page 7 + Figure 3: Correction of MERRA-2 data for 1980-2004. Why didn't you use monthly mean differences for the correction in April-August? There seems to be a clear month-dependent difference. You can still see a month-dependent difference in the corrected data ranging from -5% to 5%.
Page 9, line 25: "The estimated ozone variability is relatively low, about 15 DU for daily averages and 10 DU for monthly
values or about 6% and 4%, respectively." -> Do you mean over the winter period April-August? Please specify.Page 11, Section 4.2. For a reader not familiar with EESC fit it is very difficult to understand what is fitted to what. You should describe the methodology in more detail, and how did you end up with the fit in the right columns of Fig. 7.
page 14, line 10: "A decline in ozone due to gas-phase ozone destruction from ODSs is probably the largest since the time for an
air parcel to travel from the tropics to high latitudes is the longest." -> Please open this statement. Is this related to the Brewer-Dobson circulation transporting ozone from the tropics to the pole? Does ODS deplete it the whole way? During which months?Citation: https://doi.org/10.5194/egusphere-2023-773-RC1 -
AC1: 'Reply on RC1', Vitali Fioletov, 21 Jul 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-773/egusphere-2023-773-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Vitali Fioletov, 21 Jul 2023
-
RC2: 'very nice paper, only rather minor comments', Mark Weber, 12 Jul 2023
This paper reports on ozone changes observed since the 1960s at the
Amundsen-Scott South Pole Station (SPO). A particular focus lies in
the winter months just before the period of rapid ozone depletion in
spring ("ozone hole period"). This time of the year is covered by full
moon (FM) measurements by Brewer and Dobson spectrophotometers
complemented by regular ozone sondes and MERRA2 reanalysis data.
Regular direct sun (DS) measurements by Brewer and Dobsons are also
used to contrast the ozone changes in the winter months to other
seasons and latitudes. Wintertime ozone declined by about 12% from the
pre-1980s until the late 1990s, a larger change than observed at lower
latitudes and in other sesaons, except for the ozone hole period.The paper is well written and results are well presented. After
adressing some rather minor issues as outlined below, the paper will
be well suited for publication in ACP.p. 6, l. 15ff: A great part of the paper deals with the adjustments of
the various datasets. As a reference for adjusting all data types the
long-term Dobson data is used (p. 7, l. 14). For justification only the
study by Bernhard et al. (2005) is cited. I think a few more sentences
are here needed to explain why the Dobson record is most suitable as a
refence dataset here.p. 7, l. 32: "... remove that bias for some of the plots". So the
corrections are only applied in the plots but not for the data. I find
this a bit awkward, why not say simply the data has been corrected,
which would be important if the adjusted data im made publicly
available (see my later comments on Data Availability)p. 8, l. 5: I think that the bottom panel is not showing what is
described in the main text and figure caption. MERRA2 data are the
same as in the top panel, but all other data have been adjusted (not
the other way around).p. 11, l. 5: "four seasons" --> "three seasons"
p. 11., l. 25: not clear what is meant with "analysis of the
residuals". Please specify. A fit of only the EESC curve to the data
will result in large residuals as the short-term variability is not
fitted. Maybe it would be good to show some plots of residuals to make
the point here (could be put in the appendix).Fig. 8 (and other plots): Light blue color lines are dificult to
distinguish, in particular with different line styles. The light blue
color is not a particular good color for color blind people. I
strongly suggest to use a different color. This applies also for the
other plots using the same color.p. 14, l. 7: "Rapid ozone destruction on polar stratospheric clouds in
the springtime Antarctic vortex affects ozone levels in subsequent
months everywhere in the southern hemisphere, but its impact on the
polar ozone should be at least as strong as anywhere else." I find
this sentence a bit awkward. I think what was meant to be said is that
the polar ozone loss (ozone ozone hole) is not affecting the
wintertime ozone, so that gas-phase chemistry is only relevant in
winter. Apart from ODS gas-phase chmistry some dynamic contributions can
not be ruled out as suggested in the main text. I think this should be
mentiond here as well.p. 14, l. 17: The data at SPO, in particular the adjusted data
should be made available publicly for tracability.p. 34, l. 4: "in increasing" --> "is increasing"
Citation: https://doi.org/10.5194/egusphere-2023-773-RC2 -
AC2: 'Reply on RC2', Vitali Fioletov, 21 Jul 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-773/egusphere-2023-773-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Vitali Fioletov, 21 Jul 2023
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Vitali Fioletov
Xiaoyi Zhao
Ihab Abboud
Michael Brohart
Akira Ogyu
Reno Sit
Sum Chi Lee
Irina Petropavlovskikh
Koji Miyagawa
Bryan J. Johnson
Patrick Cullis
John Booth
Glen McConville
C. Thomas McElroy
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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