Sea ice data assimilation in ORAS6

Browne, Philip; de Boisseson, Eric; Keeley, Sarah; Pelletier, Charles; Zuo, Hao

doi:10.5194/tc-20-3299-2026

Articles | Volume 20, issue 6

https://doi.org/10.5194/tc-20-3299-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/tc-20-3299-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 6

Research article

|

03 Jun 2026

Research article |

| 03 Jun 2026

Sea ice data assimilation in ORAS6

Philip Browne, Eric de Boisseson, Sarah Keeley, Charles Pelletier, and Hao Zuo

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Final revised paper (published on 03 Jun 2026)
Preprint (discussion started on 19 Sep 2025)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-3991', Anonymous Referee #1, 18 Oct 2025

Please see the attached file.

Citation: https://doi.org/10.5194/egusphere-2025-3991-RC1
- AC1: 'Reply on RC1', Philip Browne, 02 Dec 2025
  
  Thank you to the reviewer for taking the time to provide excellent constructive comments which should help improve the manuscript.
  Please see the pdf file for our replies to each point.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3991-AC1
RC2:
'Comment on egusphere-2025-3991', Anonymous Referee #2, 21 Oct 2025

Please see the attached file.

Citation: https://doi.org/10.5194/egusphere-2025-3991-RC2
- AC2: 'Reply on RC2', Philip Browne, 02 Dec 2025
  
  Thank you to the reviewer for taking the time to provide excellent constructive comments which should help improve the manuscript.
  Please see the attached supplement for responses to each of the comments.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3991-AC2
RC3:
'Comment on egusphere-2025-3991', K. Andrew Peterson, 03 Dec 2025

Attached as pdf.

Citation: https://doi.org/10.5194/egusphere-2025-3991-RC3
- AC3: 'Reply on RC3', Philip Browne, 15 Dec 2025
  
  Thank you to the reviewer for taking the time to provide excellent constructive comments which should help improve the manuscript.
  Please see the attached supplement for responses to each of the comments.
  
  Citation: https://doi.org/10.5194/egusphere-2025-3991-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Publish subject to revisions (further review by editor and referees) (07 Jan 2026) by Ed Blockley

AR by Philip Browne on behalf of the Authors (11 Feb 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (20 Feb 2026) by Ed Blockley

RR by Anonymous Referee #1 (04 Mar 2026)

Suggestions for revision or reasons for rejection

The authors have made a number of constructive revisions in response to the reviewer comments, and I appreciate their efforts to clarify terminology, expand discussion of limitations, and improve aspects of the manuscript. In particular, the clarification regarding the intended meaning of “orthogonal,” the rewording of statements implying model “accuracy,” and the expanded discussion of limitations related to sea ice thickness constraints have improved the conceptual framing of the study.

However, several areas would still benefit from further refinement prior to publication:

1. Figures and Presentation
While some corrections were made, the figures would benefit from more thorough revision. In particular, color bar labels should be incorporated directly into the figures themselves rather than relying solely on LaTeX annotations, and care should be taken to ensure aspect ratios are not distorted. Clear, self-contained figures are essential for reproducibility and long-term usability of the published work.

2. α Sensitivity and Physical Justification
The explanation for restricting α to values ≤ 5 is clearer in the revision, but given that multiple reviewers independently raised this issue, the manuscript would benefit from a slightly more explicit justification within the main text. Even if additional experiments are not feasible, the rationale for parameter bounds and the implications for ocean thermodynamic balance should be clearly stated so that readers understand both the strengths and limitations of the approach.

3. Conclusions and Framing
The expanded discussion of why ice-induced temperature increments produce the largest performance gain is welcome. The conclusion could still be strengthened by more clearly separating (i) demonstrated findings from (ii) speculative future developments, so that the primary contributions of the present study stand out more distinctly.

Overall, the manuscript presents a meaningful technical contribution to operational sea-ice data assimilation. With continued attention to clarity of presentation, parameter justification, and figure quality, it will be well positioned for publication.

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RR by K. Andrew Peterson (05 Mar 2026)

ED: Publish subject to minor revisions (review by editor) (10 Apr 2026) by Ed Blockley

AR by Philip Browne on behalf of the Authors (16 Apr 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (17 Apr 2026) by Ed Blockley

AR by Philip Browne on behalf of the Authors (22 Apr 2026)

Short summary

An initial estimate of sea ice conditions are required to start modern weather forecasting models. To get these we have to combine observations, typically from satellites, with previous estimates of the sea ice conditions. This paper talks about how we do this in the latest version of the model, where the sea ice state has to be specified for ice of different thicknesses. We describe the method that is used when we produce an estimate for every hour for the past 50 years.