Contribution of atmospheric circulation to recent off-shore sea-level variations in the Baltic Sea  and the North Sea

Karabil, Sitar; Zorita, Eduardo; Hünicke, Birgit

doi:https://doi.org/10.5194/esd-9-69-2018

Articles | Volume 9, issue 1

https://doi.org/10.5194/esd-9-69-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

Multiple drivers for Earth system changes in the Baltic Sea...

https://doi.org/10.5194/esd-9-69-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 9, issue 1

Research article

|

18 Jan 2018

Research article |

| 18 Jan 2018

Contribution of atmospheric circulation to recent off-shore sea-level variations in the Baltic Sea and the North Sea

Sitar Karabil, Eduardo Zorita, and Birgit Hünicke

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Final revised paper (published on 18 Jan 2018)
Preprint (discussion started on 27 Mar 2017)

Interactive discussion

Status: closed

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

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RC1: 'Review of “Contribution of atmospheric circulation to recent off-shore sea-level variations in the Baltic Sea and the North Sea” by Sitar Karabil, Eduardo Zorita, and Birgit Hünicke, submitted for publication in Earth System Dynamics', Anonymous Referee #1, 13 Apr 2017
- AC1: 'Response_to_esd-2017-23-RC1', Sitar Karabil, 13 Jun 2017
RC2: 'Referees comments on "Contribution of atmospheric circulation to recent off-shore sea-level variations in the Baltic Sea and the North Sea"', Anonymous Referee #2, 28 Apr 2017
- AC2: 'Response_to_esd-2017-23-RC2', Sitar Karabil, 13 Jun 2017

Peer-review completion

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

ED: Reconsider after major revisions (29 Jun 2017) by Markus Meier

AR by Sitar Karabil on behalf of the Authors (09 Aug 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (27 Aug 2017) by Markus Meier

RR by Anonymous Referee #2 (11 Sep 2017)

Suggestions for revision or reasons for rejection

General Comments

The revised manuscript

Contribution of atmospheric circulation to recent off-shore sea-level variations in the Baltic Sea and the North Sea

by

Sitar Karabil, Eduardo Zorita, Birgit Hünicke

has improved from the version that was under review. The final section of the paper is now more readable and does summarize the results and the interpretations. The conclusions that can be drawn from the paper are clearly formulated. The suggested mechanisms provide material for future studies.

Most of the suggestions, questions and comments raised on the initial review have been addressed. After consideration of some technical corrections I recommend the manuscript for publication.

The paper addresses a relevant scientific question and presents a new approach on the interpretation of interannual sea level variability in the Baltic Sea. The main conclusion that sea level variability in the Baltic Sea is more strongly and spatially more homogeneously correlated to the the BANOS index than the NAO index is supported by the results. The assumptions and methods are valid and clearly outlined and the reproducibility and traceability is possible. The paper cites related work and puts into context the novel contribution. Title and abstract are appropriate. The manuscript is well structured and the language is fluent. Mathematical symbols and physical units are correctly used. The Technical Corrections below suggest some corrections to the text. The references and supplementary material are appropriate.

Technical Corrections

page 2, line 15: centred over the Azores
page 4, line 15: pattern and whether
page 4, line 16: more stable connection in time with sea-level
page 4, line 29: observations onto a 1/4°x1/4° resolution
page 5, line 22: found in https://www.aviso.altimetry.fr/fileadmin/documents/data/duacs/Duacs2014.pdf. [Could this report be cited as a technical report by CNES/AVISO? I would make the text more readable.]
page 5, line 32f: The names of some stations listed in the PSMSL database like Smögen, Warnemünde and Travemünde are not totally correct. [I think this comment is not necessary. The discrepancy is probably due to the adoption of ASCII to represent the alphabet of other languages.]
page 7, line 8: each of the nine tide gauges
page 7, line 15: altimeter data is provided by
page 15:, line 24ff: SWnet [If possible, it would be nice to have the "net" part as an index to SW, like in equation 1.]
page 18, line 24: could flow more parallel

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RR by Anonymous Referee #3 (13 Oct 2017)

Suggestions for revision or reasons for rejection

I suggest a minor revision. I am a new reviewer and decided not to look at the
earlier reviews. I think the paper is mostly well written and almost ready to
be published.

In terms of substance, the BANOS-index is worthily introduced to the science
community and its derivation nicely presented. In general, it is plausible that
there are local, non-stationary patterns, such as the ones represented by the BANOS-index, that are
more closely associated with the North/Baltic Sea level than the NAO. Next, the
science community will decide the value of the BANOS-index by adapting (or not)
it their research.

I have a couple of more general questions. First, the correlation already
implies a linear dependence, as does the linear regression based sensitivity
analysis, what is then the value to do and present results from both
approaches? This could be explained in the Methods section.

Second, the authors compare the BANOS-index with the Dagendorf et al. (2014)
proxy. There are a number of other atmospheric circulation indices which are
more local than the NAO and may therefore explain the sea-level variability
with a comparable skill to the BANOS-index. Closest to the study region are the
Scandinavian, the Polar/Eurasian and the East Atlantic teleconnection patterns.
As these patterns are already commonly adapted, it would be fair to see at how they
co-vary with the North/Baltic Sea level.

Minor comments:
- page 1, lines 11-12. 'This circulation pattern displays a circulation pattern ...' does not make sense. Just say 'This circulation pattern is more closely ...'.
- page 3, line 7. '...snow and ice melt...'.
- page 7, line 13. '...between the closest SLA grid cell...'.
- page 8, line 1. One line paragraphs are too short. Combine this line with the paragraph starting in line 5.
- page 9, lines 12-19. The line of thinking is somewhat unclear here. I would focus on seasonally heterogeneous response instead of spatial one and write: '.. in contrast, especially seasonally quite heterogeneous ...'. This change would make the paragraph more logical, I think.
- page 9, lines 14-15. Drop the unnecessary sentence: 'We also show that heterogeneity in the following figures.'
- page 9, line 18. '... North Sea, both in the winter ...'.
- page 9, lines 18-19. 'At this stage, we investigate which patterns ...'.
- page 19, line 19. '... Stockholm, Cuxhaven and Warnemunde stations ...'.
- page 13, line 1. '...both the BANOS-index and the NAO-index (Figures 4 and 12), ...'.
- page 13, line 14. 'Given not only the relatively stable correlation ...'.
- page 13, line 14. '...coastal sea-level variations compared to the NAO.
- page 13, line 22. Make this sentence the last one of the previous paragraph.
- page 14, line 2. I would say: 'depending on the exact location of the SLP grid cells selected to construct the BANOS-index ...'. You have already defined the BANOS-index to be based on variable SLP grid cell locations.
- page 14, line 11. Just say geostrophic winds instead of horizontal gradients in air pressure. It is clearer to the reader.
- page 14, lines 12-14. What confuses me is that you mention net energy flux variations, but not that these variations change the heat content of water and therefore the sea level. Freshwater variations, or net precipitation, is then related to the mass flux. Would make the text clearer and more reader-friendly to be specific.
- page 14, line 30. '...of sea-level and the SLP fields...'.
- page 15. Sensitivity values should have 95% confidence intervals expressed.
- page 15, lines 15-16. I do not understand this sentence. Could it just be removed?
- page 16, lines 1-5. I do not understand why a negative (NEF,BANOS) correlation in summer implies that NEF are not responsible for the sea-level variations, while in winter they are. Wouldn't the NEF effect in summer just be the opposite to the winter one? In winter the positive BANOS is associated with increased gain of heat by the sea which contributes to increased sea-level due to the heat expansion. In summer the positive BANOS is associated with increased loss of heat by the sea, one could think of relatively cold air being advected from the Atlantic to the Baltic Sea, which then contributes negatively to sea-level. But the effect is small compared to other factors, as you found.
- page 17, line 17. What is 'this contribution'? By BANOS?
- page 17, lines 21-22. Basin-wide averaging of the freshwater flux may result in a weak BANOS link because precipitation is a rather local phenomena. Some localities seem show rather high correlations adjacent to regions of low correlations. Would the averaging explain the weak winter contribution?
- page 18, line 24. '...flow more parallel...'.
- page 18, line 25. 'west-east' should be 'south-east' as the wind vectors in Figure 17?
- page 18, lines 22-26. Would a better way to think about the wind contribution be to assume that the BANOS-related winds as anomalies modifying the average climatological atmospheric wind field? In that case, one could argue that is possible that certain BANOS-conditions may assist the water to flow from the North Sea to the Baltic Sea through the Danish Straits. This seems plausible when looking at the Ekman transport vectors in Figure 17.
- page 18, lines 30-31. Add 'thermal expansion' for clarity.
- page 18, lines 29-32. This is an exiting mechanism of coastal sea-level increase, but it could be explained more clearly. Now it is very hard to understand. Are you pointing to the possibility that deep water column expand laterally more effectively than the shallower ones due to the pressure dependence of the sea-water equation of state?
- page 19, You could write about potential applications using the BANOS index. This would promote its use among the readers.

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ED: Publish subject to minor revisions (review by Editor) (13 Oct 2017) by Markus Meier

AR by Sitar Karabil on behalf of the Authors (04 Nov 2017) Author's response Manuscript

ED: Publish as is (22 Nov 2017) by Markus Meier

AR by Sitar Karabil on behalf of the Authors (27 Nov 2017)

Short summary

We analysed the contribution of atmospheric factors to interannual off-shore sea-level variability in the Baltic Sea region. We identified a different atmospheric circulation pattern that is more closely linked to sea-level variability than the NAO. The inverse barometer effect contributes to that link in the winter and summer seasons. Freshwater flux is connected to the link in summer and net heat flux in winter.The new atmospheric-pattern-related wind forcing plays an important role in summer.