The role of the winter residual circulation in the  summer mesopause regions in WACCM

Kuilman, Maartje Sanne; Karlsson, Bodil

doi:https://doi.org/10.5194/acp-18-4217-2018

Articles | Volume 18, issue 6

https://doi.org/10.5194/acp-18-4217-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-4217-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 6

Research article

|

28 Mar 2018

Research article |

| 28 Mar 2018

The role of the winter residual circulation in the summer mesopause regions in WACCM

Maartje Sanne Kuilman and Bodil Karlsson

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Final revised paper (published on 28 Mar 2018)
Preprint (discussion started on 11 Sep 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Atmospheric coupling', Anonymous Referee #2, 22 Sep 2017
- AC1: 'Response to reviewer #2', Maartje Kuilman, 19 Dec 2017
RC2: 'Review of manuscript acp-2017-647', Anonymous Referee #1, 09 Oct 2017
- AC2: 'Response to reviewer #1', Maartje Kuilman, 19 Dec 2017

Peer-review completion

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

AR by Maartje Kuilman on behalf of the Authors (19 Dec 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Dec 2017) by Bernd Funke

RR by Anonymous Referee #2 (04 Jan 2018)

Suggestions for revision or reasons for rejection

Second Review of “The role of the winter residual circulation in the summer mesopause regions in WACCM” by Maartje Kuilman and Bodil Karlsson (acp-2017-647).

The authors have implement the reviewer comments well and thus increased the readability and plausibility of their arguments. Therefore, I recommend publication after processing of the following minor and mostly technical comments.

Minor comments:
o Line 654: …relatively freely up into the mesosphere…
o Line 752 – 754: Please remove this sentence, since NLC are not a part of the paper anymore
o Line 791: is based on …
o Line 794: In this study, the F_200_WACCM …
o Line 829 – 833: Here the assumption is made that the altitude of the zonal wind reversal is correct in WACCM. However, it is not \cite. Please mention that fact.
o Line 845 – 847: Just a curious question: What is about the meridional temperature gradient when the summer polar mesopause warms as well?
o Line 851: … NLC region is about 210-22K, which is much higher …
o Line 858: They attributed that the warming …
o Line 890: …and in the summer mesopause region outside the polar region. -> The correlation is weak and not significant in the polar mesosphere (see Fig. 2 and 4).
o Line 939: … change due to turning off the winter GWs …
o Line 971: In Fig. 2, it is seen …
o Line 973: … in the NH summer polar mesosphere. -> the correlation in the polar mesosphere is weak and not significant
o Line 976: …temperature in the summer polar mesosphere. -> Same as above.
o Line 981: … is a change in the stratospheric meridional temperature gradient…
o Line 987: This can been shown clearly …
o Line 1020 -2024: The statement of this sentence is not clear.
o Line 1033: … has a net cooling effect on the summer polar mesosphere differing in magnitude between the two hemispheres.
o Line 1046: …: in this case a weak BDC leads to cooling of the summer mesosphere region.
o Line 1047 – 1049: please rewrite this sentence to make it clearer that the net effect of the IHC is probably larger than that of the intrahemispheric coupling from the stratosphere of the summer hemisphere.

Additionally, it should be mentioned in the conclusion that the positive correlation between the winter stratosphere and summer mesosphere only barely reaches the polar mesopause region.

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RR by Anonymous Referee #1 (09 Jan 2018)

Suggestions for revision or reasons for rejection

Review of manuscript acp-2017-647: “The role of the winter residual circulation in the summer mesopause regions in WACCM”, by Maartje S. Kuilman and Bodil Karlsson.

The authors have substantially reduced the length of the manuscript, and modified part of the text, in response to my comments. I think the paper goes more to the point, and thus has improved. However, I am not fully convinced about the novelty of the results; the response of the authors to this concern has been a bit vague.
I am somewhat torn on what to recommend for this paper. I think there is some interest in these results, but I believe the paper needs some new figures and a clarification of certain aspects of the presentation of the results, before it is ready for publication.

Major concerns

- What is the motivation for trying to reproduce KB16 results with WACCM? Are there processes included in WACCM and not in KMCM that justify the study?
I am not entirely satisfied with the response given to this question. WACCM includes a chemistry module in the middle atmosphere, and has different GW parameterizations and dynamical cores than those in KMCM. But this is generally true for any pair of general circulation models. What have we learned from this paper that we did not know from the previous papers, particularly KB16?
With this comment I would like to encourage the authors to find an attractive way to present the results and highlight their relevance. The way the paper is motivated in the Introduction section (and the way the results are summarized in the Conclusions section), gives me the impression that the paper is an exercise of reproducibility of previous results – which is always good news, but perhaps not enough for an article to be published in ACP.

- Figures 1 and 2. These figures show two things: 1) the IHC mechanism controls the mean T of the summer polar mesopause (Fug. 1); and 2) that T in the summer polar mesopause does not covary statistically significantly with T in the winter stratosphere (Fig. 2). The authors seem to use interchangeably “summer mesopause” and “summer polar mesopause” throughout the paper; but Fig. 2 shows that the summer mesopause away form the pole has statistically significant anomalies of T, while this is not the case for the polar region.
So what controls the summer polar mesopause T in a climatological (average) sense? IHC is clearly shown to play a role. It would also be nice to mention that the presence of GW in the summer hemisphere is a crucial factor, as shown in the response figures. Without them, the summer polar mesopause will be very high (or even absent).
As for the interannual variability, the IHC only seem to reach 50N, but not further north (line 376-383).

- I really think the paper would benefit from including plots of the EP flux divergence and the Tranformed Eulerian Mean velocities (either v* or w*). Those are more direct measures of the wave forcing and the BDC than stratospheric T, and they should not be difficult to compute from monthly mean output (WACCM does provide output of zonal mean flux diagnostics v’T’, u’v’ etc that speeds up the process). And this way I believe it would add value to the results as compared to KB16.

Specific comments:

- Line 133. Analogically → Analogously?

- Line 176. Simply WACCM since it has already been defined.

- Line 272: degrees → K (Kelvin).

- Line 280. They attributed that the warming → They attributed the warming.

- Line 288: turning of → turning off

- Lines 289-290. I may have misunderstood it, but if T in the equatorial mesosphere has a different sign in both models, there is no qualitative agreement.

- Line 343: less effect → weaker effect.

- Lines 358. It seems not quite conventional to use T in the extratropics as a proxy for the strength of the BDC, when the model provides with all the variables needed to calculate it. Please comment on this choice.

- Line 386. I do not understand this sentences. Does it mean that the BDC modifies the summer stratospheric meridional gradient of T?

- Lines 395-398. But in Fig. 2 we see that the anomalies are not statistically significant.

- Lines 468-471. “… it is the equatorial mesosphere that is governing the temperature in the summer mesopause regions...”. I agree, but the equatorial T is ultimately driven by the BDC changes forced by the winter planetary wave forcing, according with your results.

- The authors may consider to include the first part of section 3 in a new section 3.1, and rename the old section 3.1 as section 3.2 (for a matter of symmetry in the presentation).

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ED: Reconsider after major revisions (09 Jan 2018) by Bernd Funke

AR by Maartje Kuilman on behalf of the Authors (14 Feb 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (15 Feb 2018) by Bernd Funke

RR by Anonymous Referee #1 (23 Feb 2018)

ED: Publish as is (23 Feb 2018) by Bernd Funke

Short summary

In this study, we investigate the role of the winter residual circulation in the summer mesopause region using the Whole Atmosphere Community Climate Model. In addition, we study the role of the summer stratosphere in shaping the conditions of the summer polar mesosphere. We strengthen the evidence that the variability in the summer mesopause region is mainly driven by changes in the summer mesosphere rather than in the summer stratosphere.