Evidence for energetic particle precipitation and quasi-biennial oscillation modulations of the Antarctic NO<sub>2</sub> springtime stratospheric column from OMI observations

Gordon, Emily M.; Seppälä, Annika; Tamminen, Johanna

doi:https://doi.org/10.5194/acp-20-6259-2020

Articles | Volume 20, issue 11

https://doi.org/10.5194/acp-20-6259-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-6259-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 11

Research article

|

02 Jun 2020

Research article |

| 02 Jun 2020

Evidence for energetic particle precipitation and quasi-biennial oscillation modulations of the Antarctic NO₂ springtime stratospheric column from OMI observations

Emily M. Gordon, Annika Seppälä, and Johanna Tamminen

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Final revised paper (published on 02 Jun 2020)
Preprint (discussion started on 06 Dec 2019)

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Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'review', Anonymous Referee #1, 08 Jan 2020
- AC1: 'Author response to Reviewer 1', Annika Seppälä, 13 Mar 2020
RC2: 'Review of Gordon et al., EPP-NOx in Antarctic springtime and influence of the QBO', Anonymous Referee #2, 16 Jan 2020
- AC2: 'Author responses to Reviewer 2', Annika Seppälä, 13 Mar 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Annika Seppälä on behalf of the Authors (19 Mar 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (27 Mar 2020) by Thomas von Clarmann

RR by Anonymous Referee #1 (31 Mar 2020)

Suggestions for revision or reasons for rejection

The authors have addressed most of my comments satisfactorily, however I still have two concerns regarding the discussion of the QBO influence (section 4.1) and the influence of PSCs (section 4.2):

Regarding section 4.1, the sentence "Our results suggest that although the there is increased pool of N2O in polar region during eQBO contributing to larger NO2 column from N2O oxidation, EPP still contributes a clear fraction to the overall SH polar stratospheric column NO2 in the springtime" needs grammatical revision. Apart, while the revised interpretation provides an explanation for larger overall NO2 columns during QBOe years (independently on geomagnetic forcing) as indicated by Figures 3, 4, and 7a, it is not clear why the NO2-Ap correlation is more robust in QBOe years (see Figure 5), even when the analysis is restricted to the polar vortex (Figure 7 b and c). Although a deeper analysis of posible reasons might be beyond the scope of this papers, I think that this behavior should at least be mentioned.

Regarding section 4.2, to my opinion the analysis of MLS temperatures is not a stringent test whether the QBO phase affects denitrification, primarily because a lower mean temperature during QBOw does not necessarily imply a larger PSC area (this would be the case only if the area with temperature below the PSC threshold is larger in QBOw). In order to test the QBO impact on PSC formation one needs to look at the PSC areas as obtained e.g. from CALIPSO observations (see Fig. 13 of Pitts et al., 2018, www.atmos-chem-phys.net/18/10881/2018/, for the winters discussed here). Further, the bulk of PSC formation, particularly at altitudes above 20 km, occurs already in July-August, while the largest differences in MLS HNO3 are found in September (Fig 8b). Therefore I suggest to either extend section 4.2 by inclusion of additional analysis (including PSC observations) or to weaken related statements (i.e., l 5-9, l 100-102, and l 270 of the revised manuscript).

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RR by Anonymous Referee #2 (08 Apr 2020)

ED: Publish subject to minor revisions (review by editor) (09 Apr 2020) by Thomas von Clarmann

AR by Anna Wenzel on behalf of the Authors (29 Apr 2020) Author's response

ED: Publish as is (30 Apr 2020) by Thomas von Clarmann

Short summary

The Sun constantly emits high-energy charged particles that produce the ozone destroying chemical NO_x in the polar atmosphere. NO_x is transported to the stratosphere, where the ozone layer is. Satellite observations show that the NO_x gases remain in the atmosphere longer than previously reported. This is influenced by the strength of atmospheric large-scale dynamics, suggesting that there are specific times when this type of solar influence on the Antarctic atmosphere becomes more pronounced.

Evidence for energetic particle precipitation and quasi-biennial oscillation modulations of the Antarctic NO2 springtime stratospheric column from OMI observations

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Evidence for energetic particle precipitation and quasi-biennial oscillation modulations of the Antarctic NO₂ springtime stratospheric column from OMI observations