Is there a direct solar proton impact on lower-stratospheric ozone?

Jia, Jia; Kero, Antti; Kalakoski, Niilo; Szeląg, Monika E.; Verronen, Pekka T.

doi:https://doi.org/10.5194/acp-20-14969-2020

Articles | Volume 20, issue 23

https://doi.org/10.5194/acp-20-14969-2020

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

https://doi.org/10.5194/acp-20-14969-2020

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

Articles | Volume 20, issue 23

Research article

|

04 Dec 2020

Research article |

| 04 Dec 2020

Is there a direct solar proton impact on lower-stratospheric ozone?

Jia Jia, Antti Kero, Niilo Kalakoski, Monika E. Szeląg, and Pekka T. Verronen

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Final revised paper (published on 04 Dec 2020)
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Preprint (discussion started on 12 May 2020)
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Interactive discussion

Status: closed

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

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RC1: 'Comment on "Is there a direct solar proton impact on lower stratospheric ozone?"', Anonymous Referee #1, 08 Jun 2020
RC2: 'Referee comment on "Is there a direct solar proton impact on lower stratospheric ozone?" by Jia et al.', Anonymous Referee #2, 09 Jun 2020
AC1: 'Authors response to the comments', Jia Jia, 06 Aug 2020

Peer-review completion

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

AR by Jia Jia on behalf of the Authors (06 Aug 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Aug 2020) by Gabriele Stiller

RR by Anonymous Referee #2 (06 Sep 2020)

RR by Anonymous Referee #1 (07 Sep 2020)

Suggestions for revision or reasons for rejection

I am well content with the changes made, which addressed all the points I raised in the first round, and which (I think) improved the paper a great deal; it is now ready for publication. Below are listed a few technical points I found.

Abstract, lines 20-21: “The simulation results before the Aura MLS era indicate no significant effect on the lower stratospheric ozone either” – while this is factually correct, and you mention that you can’t expect this due to the energy limitation, the way it is put here gives too much weight to this sentence. Maybe you could turn around the last three sentences – it still would state the same things, but would sound slightly different: “Due to the input proton energy threshold of > 300 MeV, the model can only detect direct proton effects above 25 km, and simulation results before the Aura MLS era indicate no significant effect on the lower stratospheric ozone. However, we find a very good overall consistency between model results and MLS observations of SPE-driven ozone anomalies both on average, and for the individual cases including January 2005.” … one might argue, by the way, that this means the ozone deficit in the lowermost stratosphere after the January 2005 event is more likely due to a dynamical feedback. I’ll leave it to you whether you want to add that.

Page 3, line 9: more likely the size of the satellite footprint, not the resolution. At least across track; the distance between two footprints in the longitudinal will be much larger than 500 km.

Page 4, line 10: before the next event happens – you mean before the next event starts.?

Page 4, line 11: What do you mean by “The ionization rates to the atmosphere” ? Do you mean “The atmospheric ionization rates were than derived by averaging … “ ? Please clarify.

Page 4, line 13: … 177 events that occurred in “the complete” WACCM-D simulation period.

Page 5, line 3: “compositing” – you mean “composite analysis” I think. At least that’s the other name I know this by.

Page 5, line 13: Note the formatting of the reference (Denton et al.), the year is missing.

Page 5, Figure 15: Note you stated that the threshold for SPEs is 2 cm-1s-1, but in the figure the threshold of visibility appears to be much higher, probably 20 cm-1s-1? Can you adapt that, please?

Page 6, line 1: “that these extracted signatures are likely related to SPE” …. “that these extracted signatures are likely not random, but driven by some external forcing.” Note that particularly during polar winter, this might be dynamics/temperature as well.

Page 6, line 6: “occurred” – “occurring”

Page 6, lines 18-20: “However, since this variation starts already several days before the epoch, we cannot exclude the possibility …” as you now have restricted yourself to isolated SPEs, you can make this statement.

Page 7, line 18: true, but also true for the superposed epoch; significant results mean that they are probably not random, but that does not necessarily mean they are driven by the SPE.

Page 9, Figure 5: interesting Figure. What strikes me here: a) WACCM and MLS are really remarkably similar, at least qualitatively. B) The ozone deficit below ~20 km in WACCM can not be due to a direct impact of the proton forcing, suggesting some dynamical or radiative (how, though?) feedback. C) all ozone deficits below 40 km occur a few (~5?) days after the event onset – is that the day of the GLE? Or does that suggest a dynamical effect?

Page 10, line 14/15: yes I agree – that is an interesting event.

Page 11, line 6: Recent studies have reported “observations of” up to 10% ….

Page 11, line 16-18: … as confirmed by the case-by-case study.

Page 11, line 26: “over 20 km” – “above 20 km”, actually, what you mean is “below 25 km”, as there is an ozone deficit after the event down to 15 km, and this can’t be explained by direct proton forcing (in WACCM) either.

Page 11, lines 28-29: maybe you should stress this - the January 2005 event was followed by a GLE, but the SPE was not the strongest on record by far, see Figure 1.

Page 11, line 31: “natural variability” – you mean “random variability”. The SPE is “natural”.

Page 11, line 32: “We encourage further research …” that raises the question why you don’t do it yourself … maybe better “We note that further research is necessary, but outside the scope of this paper”

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ED: Publish subject to minor revisions (review by editor) (07 Sep 2020) by Gabriele Stiller

AR by Jia Jia on behalf of the Authors (09 Sep 2020) Author's response Manuscript

ED: Publish subject to technical corrections (08 Oct 2020) by Gabriele Stiller

AR by Jia Jia on behalf of the Authors (08 Oct 2020) Manuscript

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Short summary

Recent studies have reported up to a 10 % average decrease of lower stratospheric ozone at 20 km altitude following solar proton events (SPEs). Our study uses 49 events that occurred after the launch of Aura MLS (July 2004–now) and 177 events that occurred in the WACCM-D simulation period (Jan 1989–Dec 2012) to evaluate ozone changes following SPEs. The statistical and case-by-case studies show no solid evidence of SPE's direct impact on the lower stratospheric ozone.