Quantification of ice production in Laptev Sea polynyas and its sensitivity to thin-ice parameterizations in a regional climate model

Gutjahr, Oliver; Heinemann, Günther; Preußer, Andreas; Willmes, Sascha; Drüe, Clemens

doi:https://doi.org/10.5194/tc-10-2999-2016

Articles | Volume 10, issue 6

https://doi.org/10.5194/tc-10-2999-2016

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

https://doi.org/10.5194/tc-10-2999-2016

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

Articles | Volume 10, issue 6

Research article

|

09 Dec 2016

Research article |

| 09 Dec 2016

Quantification of ice production in Laptev Sea polynyas and its sensitivity to thin-ice parameterizations in a regional climate model

Oliver Gutjahr, Günther Heinemann, Andreas Preußer, Sascha Willmes, and Clemens Drüe

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Final revised paper (published on 09 Dec 2016)
Preprint (discussion started on 25 May 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 the Laptev Sea Polynya paper', Anonymous Referee #1, 28 Jun 2016
- AC1: 'Reply to Reviewer #1', Oliver Gutjahr, 29 Aug 2016
  - AC2: 'Appendix', Oliver Gutjahr, 29 Aug 2016
RC2: 'Referee Comment', Anonymous Referee #2, 01 Jul 2016
- AC3: 'Reply to Reviewer #2', Oliver Gutjahr, 29 Aug 2016

Peer-review completion

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

AR by Oliver Gutjahr on behalf of the Authors (22 Sep 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Sep 2016) by Dirk Notz

RR by Anonymous Referee #1 (10 Oct 2016)

Suggestions for revision or reasons for rejection

Review of
“Quantiﬁcation of ice production in Laptev Sea polynyas and its sensitivity to thin-ice parameterizations in a regional climate model”

by

Oliver Gutjahr et al.

This paper describes a range of different set-ups for a high resolution atmospheric model simulating polynyas in the Laptev Sea. The set-up involves the use of “tiles” which are sub-grid scale parametrization of thin sea ice. The quality of the model and citations are generally fine. Polynyas are important regions with substantial ice production and very high heat fluxes, and are thus an important part of the Cryosphere.

The authors have made a decent attempt at re-writing the paper, and much of the overly detailed text has been removed, and a more general introduction has been added, compared to the first version.

For the main conclusion some new conclusions about the atmospheric boundary layer has been added, where the model actually should resolve processes in a better way than earlier model attempts. That the overall heat loss increases along with the total ice production when areas of thinner ice is added as a new lower boundary condition is indeed what is expected and does not contribute to an increased scientific understanding. I still find that the changes needed falls into the “major” category – as outlined below.

Major comments:

No discussion and explanation of increasing winds with thinner ice cover.

Figures 4, 5, 6, and 10 have too small labels, legends and arrows.

MODIS based thin ice categories (Fig. 12) “explains” the thin ice tiles, and needs to be presented before the different simulations.

“Realistic” assumptions versus “”reference simulation” needs a better explanation and introduction. Why is the most realistic simulation not the reference? I think this is caused be previous simulations with the same model, but it is not well explained.

“Dense bottom water” formation is only added to the abstract and conclusion, but no results are present illustrating the possible consequences of a larger or smaller ice production, and no citations are given for such estimates either.

Detailed comments:

Abstract:

You should not use abbreviations in here, please spell out all words properly. And define them first time in the main text.

The last sentence on “global thermohaline circulation” should be removed, this might serve as a motivation for the study, but no results are given, and there is no discussion on this aspect either.

Line 8: ice production was estimated.

Introduction:

Pge 1, Line 22: No citation on ocean circulation, just for atmosphere. Either remove “ocean circulation” or find a proper citation at least.

Page 3, line 7-8: Again the global importance has no citation, and suggests wishful thinking of your own favourite process ….

Page 4, line 8: should be “proxy for dense water formation”.

Lines 9 – 18: This is very detailed text that describes your model setup, it clearly belongs in the methods section.

Section 2:
Page 6, Line 5: spell “outside” correctly.

Line 8: contradiction of terms here “open water areas are rarely free of ice” ….. What you mean is that there is usually a mix of open water and grease/frazil and thin solid ice in a polynya. The images supplied in the answer are clearly taken on calm days with little wind pushing ice away from the “up-wind” side.

Section 4:
Please use “evaluation” instead of “verification”, you can never, ever, verify that a model works perfectly, it is always a model of the real thing – nature. Otherwise this section is quite convincing, and very good that you have AWS observations available.

Section 5:
Page 12, line 2: the SIC is between 0% and 7%.

Line 21-22: The most interesting results to me is that the winds do increase when you use a thinner ice cover. This also seems to explain much of the changes in heat flux. Why is this so? You do not discuss this.

Figure 7: Letters H, E, L and K needs to be explained in the caption.

Page 16, line 1: Again the increasing wind – lacking explanation.

Line 4: “the location of clouds vary”

Page 17, line 7: The “realistic configuration” is not the “ref” model run. This is a bit odd. You made your choice though, so we can live with that. But – an explanation is need. It appears to come with the MODIS results in Figure 12. This is the background you depend upon for the model set-up, so it should be presented first.

Line 17: The “Bowen ratio” needs a citation.

Section 6

Page 18, Line 8 – 18: The polynya area is prescribed for the different model runs, and is thus model forcing. At least this is what I understand from your description. This is therefore not a result, and is part of the methods. This text should thus be moved to methods.

Page 19, line 8 and line 25: The “realistic assumptions” here needs to be explained as noted above. A different word for this run might be better.

Line 31-32: This increase in ice production and heat loss with thinner ice is NOT a result. It is zero order physics. If your model did not re-produce this basic physics you should be very worried. It is fine that it does, but it cannot be packed in as a result. There are of-course feed-back processes regulating if theresponse is linear, or not. This is the interesting bit, and a result.

Section 7:

You need to implement the wind increase explanation (Page 20, line 3), and the “realistic assumption” (Page 20, line 10).

Page 21, line 26: Is there no ice production outside the polynya? This might be a consequence of the “offline post production” – but in nature there is of course continued growth outside the polynya. Must be mentioned.

Conclusion:

I suggest that all abbreviations should be removed from the Conclusion, one should be able to read it on it’s own.

Page 22, Line 22: Please change to: “ ….based on simulations with a regional atmospheric model (CCLM)”. This is needed because many people read Conclusion first.

Line 29: Add something after “realistic assumption” as noted with “major” points. Perhaps: “for the most realistic assumptions based on remote sensing of ice thickness”.

Page 23, line 1 – 3: Here you should clearly mention that a coupled models would be benefitial. Using a slab ocean + sea ice + atmosphere would produce it’s own sea ice thickness based on the heat fluxes, as happens in nature.

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RR by Anonymous Referee #2 (10 Oct 2016)

ED: Publish subject to minor revisions (Editor review) (10 Oct 2016) by Dirk Notz

AR by Oliver Gutjahr on behalf of the Authors (19 Oct 2016) Author's response Manuscript

ED: Publish subject to technical corrections (09 Nov 2016) by Dirk Notz

AR by Oliver Gutjahr on behalf of the Authors (11 Nov 2016) Manuscript

Short summary

We estimated the formation of new sea ice within polynyas in the Laptev Sea (Siberia) with the regional climate model COSMO-CLM at 5 km horizontal resolution. Fractional sea ice and the representation of thin ice is often neglected in atmospheric models. Our study demonstrates, however, that the way thin ice in polynyas is represented in the model considerably affects the amount of newly formed sea-ice and the air–ice–ocean heat flux. Both processes impact the Arctic sea-ice budget.