A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)

Zhang, Tong; Price, Stephen; Ju, Lili; Leng, Wei; Brondex, Julien; Durand, Gaël; Gagliardini, Olivier

doi:https://doi.org/10.5194/tc-11-179-2017

Articles | Volume 11, issue 1

https://doi.org/10.5194/tc-11-179-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/tc-11-179-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 11, issue 1

Research article

|

25 Jan 2017

Research article |

| 25 Jan 2017

A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)

Tong Zhang, Stephen Price, Lili Ju, Wei Leng, Julien Brondex, Gaël Durand, and Olivier Gagliardini

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Final revised paper (published on 25 Jan 2017)
Supplement to the final revised paper
Preprint (discussion started on 16 Mar 2016)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of ``A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)''', Anonymous Referee #1, 29 Mar 2016
- AC1: 'Response to Anonymous Referee #1: “Interactive comment on A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)”', Stephen Price, 08 Jul 2016
RC2: 'tc-2016-49', Stephen Cornford, 13 Apr 2016
- AC2: 'Response to Referee #2: “Interactive comment on A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)”', Stephen Price, 08 Jul 2016
RC3: 'Report on the manuscript "A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)" by T. Zhang et al. submitted to The Cryosphere.', Anonymous Referee #3, 29 Jun 2016
- AC3: 'Response to Anonymous Referee #3: “Interactive comment on “A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)” by Tong Zhang et al.”', Stephen Price, 08 Jul 2016

Peer-review completion

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

AR by Stephen Price on behalf of the Authors (08 Jul 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 Jul 2016) by G. Hilmar Gudmundsson

RR by Stephen Cornford (12 Aug 2016)

Suggestions for revision or reasons for rejection

I had two major issues with the original manuscript, and both have been largely addressed. The first was the lack of a convergence study of the MSIMIP3d Std experiment, which is now present. The second was a tendency to insist that intercomparison exercise needed, rather than benefitted from, more than one Stokes code. That has been toned down, but I still have some minor disagreements.

General Comments

The convergence study suggest an error estimate in GL position of ~300 m at dx_min = 50m. But the difference between ‘grown’ and ‘shrunk’ GLs at dx_min = 50 is ~5 km . That, together with the neither linear nor quadratic form of the Richardson estimates tells us that the FELIX-S is not in the asymptotic regime (nor is Elmer/Ice), either because a finer resolution is needed at the GL, or the region of fine resolution needs to be bigger. However, I don’t believe that anyone else has achieved better results than this. Perhaps the lesson is ‘estimate the error in as many ways as possible and take the largest number’

In the abstract, we have ‘at a particular resolution, the span of grounding lines positions provides one estimate for model error … More importantly we show that the grounding line positions appear to converge to within the estimated truncation error of Elmer/Ice’. I think this needs to be rephrased, because you always need the convergence study (different experiments result in different truncation errors), and so the model difference should never be needed as an error estimate - but might provide a useful complementary estimate where the convergence study cannot be carried to the asymptotic regime.

I noticed that the other two reviewers seemed to think this was more of a GMD paper than a TC paper. I don’t fully agree - the paper could be equally at home in GMD, but we do want glaciologists. rather than model developers, to understand the limitations of the models they choose. So I see no reason why this discussion cannot be in TC, especially since parts of it (e.g the Gagliardini 2016 paper) already are. There was also a question of novelty. There I think that, since we need results to be independently reproduced before we believe them, there must be some avenue open to publish reproduced results, especially the first reproduced results.

Specific Comments

P6, L30 : ‘very good agreement’ -> close agreement, or something that does not involve ‘very’

P7, L3: ‘the horizontal velocity’, u -> ‘ the x-component of the horizontal velocity’, u

P7, L24 ‘...superior to the other’ : and in any case should vanish as dx -> 0

P7, L26 : ‘very’ …

P7, L32: (50 m in the vicinity of the GL and 2500m , respectively) what about the x-resolution far from the GL?

P7,L34 ‘in equlibrium … based on’ -> ‘close to equilibrium… according to’

P8 L3 ‘more retreated’ -> ‘further upstream‘

P8 L35 solution error -> estimates of solution error

P9: L1 ‘clearly convergent’ -> seemingly convergent

P11, L5 ‘gradients in ice sheet geometry’ -> differences in ice sheet geometry between nodes

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RR by Anonymous Referee #1 (25 Aug 2016)

Suggestions for revision or reasons for rejection

1. General statement

The revised version of “A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)” by T. Zhang et al. includes most of the comments suggested by the reviewers, especially about the impact of grid resolution and the convergence of model results. It is greatly clarified compared to the previous version and assertions about the validity of full- Stokes are better moderated. The paper is very qualitative in several places and should include more quantitative information.

2. Specific comments

p.2 l.16-20: This statement is not justified. It is not clear why models would need comparison with Stokes models more than in the past. Futhermore, if Stokes models do not make any assumption in the stress tensor, there has not been any improvement in the treatment of grounding line with subgrid parameterization similar to what has been done for other approximations. This makes Stokes models more sensitive to grid resolution than other models.

The manuscript remains too qualitative in several places. Adverbs like “slighly” (in section 5.2 in particular, but in several other place in the text) are used very often and should be replaced by quantitative measures (e.g. “slightly thinner ice (and hence floatation) occuring slightly farther inland relative to Elmer/Ice”).

Section 5.3 explains the importance of grid resolution in both directions in getting similar results between Elmer/Ice and FELIX-S, and I think this statement should be added to the abstract along the other conclusions about experiments P75S and P75R.

3. Technical comments

p.5 l.9: “not clear” → “no clear”

p.11 l.29: “then” → “than”

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ED: Reconsider after major revisions (30 Sep 2016) by G. Hilmar Gudmundsson

AR by Anna Mirena Feist-Polner on behalf of the Authors (02 Nov 2016) Author's response

ED: Publish subject to minor revisions (Editor review) (26 Nov 2016) by G. Hilmar Gudmundsson

AR by Stephen Price on behalf of the Authors (07 Dec 2016) Author's response Manuscript

ED: Publish as is (11 Dec 2016) by G. Hilmar Gudmundsson

Short summary

Stokes-flow models are the highest-fidelity representation of the equations governing ice sheet flow and they are often treated as the standard against which other models are compared in model benchmark activities. We compare two different Stokes models applied to a canonical set of idealized marine ice sheet experiments and demonstrate that the solutions converge with increasing grid resolution. This provides confidence in the use of Stokes models for generating test case solution metrics.