Transient simulations of the present and the last interglacial climate using the Community Climate System Model version 3: effects of orbital acceleration

Varma, Vidya; Prange, Matthias; Schulz, Michael

doi:https://doi.org/10.5194/gmd-9-3859-2016

Articles | Volume 9, issue 11

https://doi.org/10.5194/gmd-9-3859-2016

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

https://doi.org/10.5194/gmd-9-3859-2016

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

Articles | Volume 9, issue 11

Methods for assessment of models

|

01 Nov 2016

Methods for assessment of models |

| 01 Nov 2016

Transient simulations of the present and the last interglacial climate using the Community Climate System Model version 3: effects of orbital acceleration

Vidya Varma, Matthias Prange, and Michael Schulz

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Final revised paper (published on 01 Nov 2016)
Preprint (discussion started on 21 Jul 2015)

Interactive discussion

Status: closed

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

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RC C1522: 'Review Varma et al.', Anonymous Referee #1, 25 Jul 2015
RC C1623: 'Is accelaration technique applicable for CGCM?', Anonymous Referee #2, 07 Aug 2015
SC C1665: 'Executive Editor Comment on "Transient simulations of the present and the last interglacial climate using a coupled general circulation model: effects of orbital acceleration"', Astrid Kerkweg, 11 Aug 2015
RC C1697: 'Comments on "Transient simulations of the present and the last interglacial climate using a coupled general circulation model: effects of orbital acceleration. Submitted by Varma, et al.', Oliver Elison Timm, 12 Aug 2015
AC C2058: 'Acknowledging the reviewers' comments', Vidya Varma, 16 Sep 2015

Peer-review completion

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

AR by Vidya Varma on behalf of the Authors (28 Apr 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 May 2016) by Didier Roche

RR by Anonymous Referee #1 (16 May 2016)

Suggestions for revision or reasons for rejection

Review of manuscript by Varma et al.
The manuscript has greatly improved and I only have some minor comments that I feel should be addressed before publication.

Lines 155-156: It is explained here (and in several figure captions) what methodology has been applied to make the time series from the non-accelerated and accelerated simulations (most) comparable. I feel this should be discussed in more depth. For instance, it could be mentioned that for comparison between the two simulations, the accelerated time series are stretched onto the non-accelerated timescale (Figure 2). Then for say a 100yr interval on this time scale, the accelerated data is represented by a single point (if I understand the manuscript correct), a 10yr average in model years that is then stretched to represent a 100 years. For the non-accelerated runs 10 10yr means are taken over which a 10-point running mean is then applied. It seems to me that the result is not completely the same. In the light of this manuscript this is not such an issue, but I think it should be mentioned, especially considering that previous and future studies might analyse results from accelerated runs in terms of decadal-millenial variability. It would be great if some advice could be given here of how such an analysis should be done, if at all, for future reference.

Lines 139-148: The manuscript nicely describes the importance of initializing the deep ocean when applying an acceleration technique. It appears to me that the difference between the initialization of the PIG and LIG simulations could impact the results. The PIG has been initialized with a 400yr 9ka simulation. However, the LIG used this simulation to start another 400yr 130ka equilibrium simulation. Assuming that the 9ka climate is closer to the 130ka climate than the pre-industrial climate is (based on the forcing one would suspect this), then in the LIG simulations the deep ocean has had more time during spin up to adjust. Could this partly explain the differences between PIG and LIG shown in figure 12?

Lines 367-368: In the conclusion section as well as at other places in the manuscript, the slow response time of the deep ocean and the impact it has on simulations applying orbital acceleration techniques are discussed in terms of the importance of initialization. I think it would be good to explain that there seem to be two effects (closely related, but nonetheless): 1) If indeed the initial climate state was not in full equilibrium this will more strongly effect an accelerated run compared to a non-accelerated run. 2) The deep ocean response to changes in the climate forcing during the transient run will have a lagged effect on the climate in an accelerated run compared to a non-accelerated run. This could be clarified in the text.

Lines 213-214: The pattern in the SH in the accelerated runs looks opposite to me, please clarify.

Lines 224-225: Perhaps a reference can be given here.

Line 291: Bracket is missing.

Lines 289-302: Have these changes in LIG convection in the North Atlantic been described before, if so please reference.

Lines 344-351: This part could be integrated into the conclusion section.

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RR by Oliver Elison Timm (27 May 2016)

ED: Reconsider after major revisions (30 May 2016) by Didier Roche

AR by Vidya Varma on behalf of the Authors (23 Jul 2016) Author's response Manuscript

ED: Reconsider after major revisions (24 Aug 2016) by Didier Roche

AR by Vidya Varma on behalf of the Authors (02 Oct 2016) Author's response Manuscript

ED: Publish as is (05 Oct 2016) by Didier Roche

Short summary

We compare the results from simulations of the present and the last interglacial, with and without acceleration of the orbital forcing, using a comprehensive coupled climate model. In low latitudes, the simulation of long-term variations in interglacial surface climate is not significantly affected by the use of the acceleration technique and hence model–data comparison of surface variables is therefore not hampered but major repercussions of the orbital forcing are obvious below thermocline.