Origins of multi-decadal variability in sudden stratospheric warmings

Dimdore-Miles, Oscar; Gray, Lesley; Osprey, Scott

doi:https://doi.org/10.5194/wcd-2-205-2021

Articles | Volume 2, issue 1

https://doi.org/10.5194/wcd-2-205-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wcd-2-205-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 2, issue 1

Research article

|

15 Mar 2021

Research article |

| 15 Mar 2021

Origins of multi-decadal variability in sudden stratospheric warmings

Oscar Dimdore-Miles, Lesley Gray, and Scott Osprey

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Final revised paper (published on 15 Mar 2021)
Preprint (discussion started on 10 Nov 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'review', Anonymous Referee #1, 06 Dec 2020
- AC1: 'Reply on RC1', Oscar Dimdore-Miles, 23 Dec 2020
RC2: 'Review for "Origins of Multi-decadal Variability in Sudden Stratospheric Warmings" (2020)', Anonymous Referee #2, 07 Dec 2020
- AC2: 'Reply on RC2', Oscar Dimdore-Miles, 23 Dec 2020
RC3: 'Review of the manuscript “Origins of Multi-decadal Variability in Sudden Stratospheric Warmings”', Anonymous Referee #3, 21 Dec 2020
- AC3: 'Reply on RC3', Oscar Dimdore-Miles, 23 Dec 2020

Peer-review completion

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

AR by Oscar Dimdore-Miles on behalf of the Authors (24 Dec 2020) Author's response

ED: Referee Nomination & Report Request started (11 Jan 2021) by Daniela Domeisen

RR by Anonymous Referee #2 (15 Jan 2021)

RR by Anonymous Referee #1 (25 Jan 2021)

For final publication, the manuscript should be

accepted as is

accepted subject to technical corrections

accepted subject to minor revisions

reconsidered after major revisions

I would be willing to review the revised paper, if the editor considers it necessary.

I am not willing to review the revised paper.

rejected

Suggestions for revision or reasons for rejection

Review of " Origins of Multi-decadal Variability in Sudden Stratospheric Warmings”
By Oscar Dimdore-Miles, Lesley Gray, and Scott Osprey

The authors satisfactorily addressed the comments from my previous review, and the paper is nearly ready for acceptance. There are just a few remaining issues to clarify.

Major comments:
1. Both another reviewer and I were a bit confused by the relatively weak relationship between the AL index the authors chose and the SSW index. The authors, in their response to reviewer 3, note that if the box is pushed further north to match the region of Garfinkel et al 2010, the correlation is even lower. I find this surprising. Supplemental Figure 6 in Schwartz and Garfinkel 2020 shows the lag correlation between 500hPa height and wave1+2 heat flux at 100hPa in the UKMO model included in the S2S database (which I assume is very similar to the configuration used in this paper), and find that a box further north is indeed more closely associated with heat flux in the lower stratosphere than what the authors include.

I think a full investigation is beyond the scope of this paper, but I wonder if the box further north is more correlated with the seasonal mean vortex, while the definition used in this paper is (apparently) more closely associated with SSW. Even if a full discussion is deferred for future work, I think this issue merits some discussion in the paper itself.

Minor comments,
Line 106: A more appropriate paper to cite than Garfinkel et al 2010 is Garfinkel et al 2020 (Climate Dynamics).

Line 542-549 and 567: Rao et al 2020 document the Holton Tan effect in the historical simulations of this model, and find that the model has a too-weak HT effect if a simple composite based on lower stratospheric winds is created (similar to most models), but does a better job if care is chosen to focus on the QBO phase that is most closely associated with the HT effect. This could be mentioned in the discussion when you mention the caveat that this is just one model, as this model does a better job than most for the HT effect.

Figure 10 and 11 are missing colorbars. If the colorbar is the same as other figures, please just note this fact.

Schwartz, Chen, and Chaim I. Garfinkel. "Troposphere‐stratosphere coupling in subseasonal‐to‐seasonal models and its importance for a realistic extratropical response to the Madden‐Julian Oscillation." Journal of Geophysical Research: Atmospheres 125, no. 10 (2020): e2019JD032043.

Garfinkel, Chaim I., Chen Schwartz, Ian P. White, and Jian Rao. "Predictability of the early winter Arctic oscillation from autumn Eurasian snowcover in subseasonal forecast models." Climate Dynamics 55 (2020): 961-974.

Rao, J., Garfinkel, C. I., & White, I. P. (2020). Impact of the Quasi-Biennial Oscillation on the Northern Winter Stratospheric Polar Vortex in CMIP5/6 Models. Journal of Climate, 33(11), 4787-4813.

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RR by Anonymous Referee #3 (27 Jan 2021)

For final publication, the manuscript should be

accepted as is

accepted subject to technical corrections

accepted subject to minor revisions

reconsidered after major revisions

I would be willing to review the revised paper, if the editor considers it necessary.

I am not willing to review the revised paper.

rejected

Suggestions for revision or reasons for rejection

The authors have addressed most of my comments and suggestions. I appreciate the efforts to improve the description of the wavelet technique and to extend the discussion of the potential role of the PDO in defining the multi-decadal variability of SSWs. I have just a couple of small comments, mostly regarding new text included during the review process.

L255: the authors indicate that the month range considered in the Aleutian low index is the same as that used for their SSWs definition. However, the months used for the SSWs definition is stated some sentences later.

L282: I would not recommend describing this model bias as cold pole bias. The cold pole bias traditionally refers to the bias of many models towards an anomalously strong climatological vortex (particularly in the Southern Hemisphere). Usually this is due to a lack of wave forcing in models. In the present study, it does not seem that the model simulates a too strong vortex, since the averaged frequency of SSWs is not that different from that in observations. Instead, the vortex is probably too weak in November and so there is an unrealistic frequency of SSWs in that month. As the vortex is recovering in the following months, the occurrence of an SSW becomes less likely. Nevertheless, it is true that it is a common problem across models as shown by Charlton et al. (2007) or more recently by Ayarzagüena et al. (2020).

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ED: Publish subject to minor revisions (review by editor) (30 Jan 2021) by Daniela Domeisen

AR by Oscar Dimdore-Miles on behalf of the Authors (03 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (09 Feb 2021) by Daniela Domeisen

AR by Oscar Dimdore-Miles on behalf of the Authors (10 Feb 2021) Author's response Manuscript

Short summary

Observations of the stratosphere span roughly half a century, preventing analysis of multi-decadal variability in circulation using these data. Instead, we rely on long simulations of climate models. Here, we use a model to examine variations in northern polar stratospheric winds and find they vary with a period of around 90 years. We show that this is possibly due to variations in the size of winds over the Equator. This result may improve understanding of Equator–polar stratospheric coupling.