The South American monsoon variability over the last millennium in climate
models

Rojas, Maisa; Arias, Paola A.; Flores-Aqueveque, Valentina; Seth, Anji; Vuille, Mathias

doi:https://doi.org/10.5194/cp-12-1681-2016

Articles | Volume 12, issue 8

https://doi.org/10.5194/cp-12-1681-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/cp-12-1681-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 8

Research article

|

19 Aug 2016

Research article |

| 19 Aug 2016

The South American monsoon variability over the last millennium in climate models

Maisa Rojas, Paola A. Arias, Valentina Flores-Aqueveque, Anji Seth, and Mathias Vuille

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Final revised paper (published on 19 Aug 2016)
Preprint (discussion started on 08 Dec 2015)

Interactive discussion

Status: closed

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

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RC C2875: 'Review of ‘The South American Monsoon Variability over the Last Millennium in CMIP5/PMIP3 simulations’ by Rojas et al.', Anonymous Referee #1, 07 Jan 2016
RC C2939: 'SAMS variability over the last millennium', Anonymous Referee #2, 17 Jan 2016
AC C3253: 'responses to Editor and reviewers', maisa rojas, 14 Apr 2016

Peer-review completion

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

ED: Reconsider after major revisions (23 Apr 2016) by Eduardo Zorita

Dear Dr. Rojas,

thank you very much for submitting your study to Climate of the Past Discussions and for responding to the reviewer’s comments in the interactive discussion phase.
Your response clearly describes how you intend to revise the manuscript addressing the concerns raised by the reviewers,
The points raised by reviewer #1 were quite substantial and are related to core methodological aspects of the study. This reviewer recommended the rejection of manuscript.
The evaluation of reviewer #2 was more positive, referring only to some particular , though also important, aspects of the study. One point raised by reviewer #2, the selection of the sub-periods, was also pointed out by reviewer #1 as worth of attention.

Reviewer #1 also considered that the study lacks a clear motivation ('hypothesis'). In your response you state that this hypothesis is that 'Given these conclusions our hypothesis is that the changes observed during those periods result from a combination of external forcing and internal variability. ' This hypothesis seems to me correct but not very informative. Climate variability must be composed of externally forced variability and internally generated variability. Therefore, my opinion is that the manuscript would benefit from a clearer and tighter exposition of your main working hypothesis. I have the impression that part of the critical evaluation by reviewer #1 originates in a unclear explanation of the main motivation of the study.

I would encourage you to carefully prepare a revised version of the manuscript along the lines of your response to the reviewers, but also taking into account my recommendation in the previous paragraph.

Best regards,

Eduardo Zorita

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AR by Maisa Rojas on behalf of the Authors (05 Jun 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Jun 2016) by Eduardo Zorita

RR by Anonymous Referee #1 (21 Jun 2016)

Suggestions for revision or reasons for rejection

Second Review of ‘The South American Monsoon Variability over the Last Millennium in CMIP5/PMIP3 simulations’ by M. Rojas et al.

General Comment

Overall I see some improvement concerning the English, but I have still major comments with respect to the presented findings. Therefore, I recommend major revisions and if the authors insist to keep the analysis of the ‘regional’ Hadley cell I recommend to reject the manuscript (see details below). Note that I used the version including the track changes.

Comments

L348: “Therefore, we use …”

L351: “… are identified”

L374: “This results in a weakening of the monsoon …”

L448: Please remove ‘derived from temperature and precipitation reconstructions’ as it is not necessary.

L450: ‘ocean heat transport’

L452: ‘freshwater’ is normally written in one word, please change elsewhere.

L510: The phrase ‘near-global temperature anomalies’ is awkward, please clarify.

L593: Please make a reference to this statement.

L594: ‘methodology’ is defined as the systematic, theoretical analysis of the methods applied to a field of study. So please use ‘analysis of’ instead of ‘methodology used to asses’.

L611: ‘conditional composite analysis’ is misleading. ‘Conditional’ is used in statistics in a very specific way.

L683: Please explain all the variables used in this formula. But as I suggest to remove the analysis of the regional Hadley cell this part needs to be rearranged.

L800/801: If most of the simulations show a southward migration of the ITCZ then it needs to be visible in the ensemble mean. If not something with the analysis is wrong.

L808-828: I suggest to remove this section from the manuscript for several reasons. As stated in the last review I am not convinced that a regional Hadley cell makes sense, although this paper of Zhang and Wang exists. Another important argument is that the results presented in the discussion phase (reply, figure of ‘global and regional’ Hadley cell) are not consistent with classical analysis of the Hadley circulation (http://onlinelibrary.wiley.com/doi/10.1029/2011JD016677/epdf Stachnik and Schumacher 2011, JGR) and the Zhang and Wang paper. The structure is different and the signs are wrong. So I have doubts that the analysis is correct. Finally, I think it is not necessary as the authors could simply analyze the vertical wind at different levels in the region of interest. They already state in the manuscript (L813) that they are interested in the areas of rising. Please also note that the references in L810 and 811 only analyze the classical Hadley cell, not the ‘regional one’.

L870: I guess that the authors refer her to the classical Hadley cell?

Section 4: You need to remove or revise the discussion on the Hadley cell.

L972: Please change to ‘Therefore, the weak temperature …’

L979-981: This is fully unclear and needs to be explained. Also the authors need to add citations.

1005-1008: There are multi proxy reconstructions for South America, e.g. from the PAGES 2K initiative: Working Groups LOTRED-SA.A few relevant publications:

Neukom, R., Gergis, J., Karoly, D., Wanner, H., Curran, M., Elbert, J., Gonzàles-Rouco, F., Linsley, B., Moy, A. D., Mundo, I. A., Raible, C. C., Steig, E. J., Van Ommen, T., Vance, T., Villalba, R., Zinke, J. and Frank, D (2014): Inter-hemispheric temperature variability over the past millennium. Nature Climate Change, 4, 362-367, doi: 10.1038/NCLIMATE2174.

PAGES 2k Consortium (2013): Continental-scale temperature variability during the past two millennia. Nature Geoscience 6: 339-346, doi:10.1038/NGEO1797

Neukom, R., Luterbacher, J., Villalba, R., Küttel, M., Frank, D., Jones, P. D., Grosjean, M., Wanner, H., Aravena, J. C., Black, D., Christie, D. A., D’Arrigo, R., Lara, A., Morales, M., Soliz-Gamboa, C., Srur, A., Urrutia, R., and von Gunten, L., (2011):Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries, Climate Dynamics, 27, 35-51.

Fig 2: There is a problem at the 0 degree longitude line in all panels. I also suggest to use white for not significant areas and colors when the differences are significant. In the caption there is a strange sign before 0.05.

Fig3a: The color scale makes no sense as we only see blue and yellow. Also treat the significance similar to Fig. 2. In the caption there is a strange sign before 0.05.

Fig.4: Wind arrows have two components so if a vector is significant does this imply that both components are significant or only one?

Fig.5: According to my suggestion this figure needs to be removed.

Fig7: You use white for two information, significance and values between -0.3 and 0.3. This is awkward so I suggest to use white for not significant areas and avoid white in the color bar.

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ED: Reconsider after major revisions (28 Jun 2016) by Eduardo Zorita

Dear Dr. Rojas,

The revised version has now been evaluated by reviewer #1. This reviewer has expressed a quite critical opinion on the initial version of the manuscript and, although the reviewer acknowledges the improvements introduced in the text and sees the potential value of your study, there still some issues that require your attention.
In particular, the section devoted to the analysis of the regional Hadley cell is problematic. I had to go back and revised the cited literature, the reviewer report and your response to get a clearer picture and this has taken some time.
In my opinion, I have to concur with the reviewer's view that this section still requires some revisions, and more importantly I cannot clear see the relevance of this section for your study, as I explain below:

1. The reviewer expresses doubts that the definition and analysis of the regional Hadley cell, in contrast to the global Hadley cell is really required. This, together with a problematic definition of the regional Hadley cell put some doubts on this part of the analysis

2 Neither the abstract nor the conclusion sections mention the results related to the local Hadley cell at all. This is for me a clear sign that you and your authors do not deem it central for your analysis.

3. In my interpretation, the literature cited in this version on 'regional' Hadley cell' (Dima and Wallace, Trenberth et al) do not really look into the regional Hadley cell, but rather at the links between the Hadley cell and regional monsoon circulations. The only paper defining a regional Hadley cell is Zhang and Wang, but although this definition may make sense from the formal point of view, I failed to see the link to main goals of your study in particular. Reviewer #1 suggests to look instead at the vertical velocities, instead of trying to separate this velocity in two components belonging to the Hadley and Walker circulation. Since the regional Hadley circulation per se does not seem to play a central role in your analysis, I find the suggestion of the reviewer to be reasonable, as this separation sounds artificial.

My reading of the other comments by the reviewer is that they can be relatively easily addressed, and I would appreciate if you could consider them as well in a revised version.

Sincerely,

Eduardo Zorita

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AR by Maisa Rojas on behalf of the Authors (09 Jul 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Jul 2016) by Eduardo Zorita

RR by Anonymous Referee #1 (25 Jul 2016)

ED: Publish subject to technical corrections (25 Jul 2016) by Eduardo Zorita

AR by Maisa Rojas on behalf of the Authors (27 Jul 2016) Author's response Manuscript

Short summary

Recent work shows that during the most prominent climate anomalies during the last millennium, the Medieval Climate Anomaly (ca. 950–1250) and the Little Ice Age (ca. 1450–1850), the South American monsoon system (SAMS) was drier and wetter, respectively. We investigate if this variability in the SAMS is reproduced in the latest set of climate simulations that cover these periods. Despite weak forcing, through analysis of the large-scale circulation we find this signal in the models.