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. |