Wintertime dynamics in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment

Vilibić, Ivica; Mihanović, Hrvoje; Janeković, Ivica; Denamiel, Cléa; Poulain, Pierre-Marie; Orlić, Mirko; Dunić, Natalija; Dadić, Vlado; Pasarić, Mira; Muslim, Stipe; Gerin, Riccardo; Matić, Frano; Šepić, Jadranka; Mauri, Elena; Kokkini, Zoi; Tudor, Martina; Kovač, Žarko; Džoić, Tomislav

doi:https://doi.org/10.5194/os-14-237-2018

Articles | Volume 14, issue 2

https://doi.org/10.5194/os-14-237-2018

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

https://doi.org/10.5194/os-14-237-2018

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

Articles | Volume 14, issue 2

Research article

|

23 Mar 2018

Research article |

| 23 Mar 2018

Wintertime dynamics in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment

Ivica Vilibić, Hrvoje Mihanović, Ivica Janeković, Cléa Denamiel, Pierre-Marie Poulain, Mirko Orlić, Natalija Dunić, Vlado Dadić, Mira Pasarić, Stipe Muslim, Riccardo Gerin, Frano Matić, Jadranka Šepić, Elena Mauri, Zoi Kokkini, Martina Tudor, Žarko Kovač, and Tomislav Džoić

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Final revised paper (published on 23 Mar 2018)
Preprint (discussion started on 24 Feb 2017)

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

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RC1: 'Review of Vilibic et al, OSD', Anonymous Referee #1, 29 Mar 2017
- AC1: 'Response to Reviewer#1 comments', Ivica Vilibic, 16 May 2017
RC2: 'Review of Manuscript “Dense water formation in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment” by Vilibic et al.', Anonymous Referee #2, 20 Apr 2017
- AC2: 'Response to Reviewer#2 comments', Ivica Vilibic, 16 May 2017

Peer-review completion

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

AR by Ivica Vilibić on behalf of the Authors (06 Jun 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Jun 2017) by Simon Josey

RR by Anonymous Referee #2 (04 Aug 2017)

RR by Anonymous Referee #1 (09 Aug 2017)

Suggestions for revision or reasons for rejection

Review #2 of Vilibic et al, OSD :

This is the second review of the manuscript « Dense water formation in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment » by Vilibic et al. The authors have provided a comprehensive response to the previous comments which is highly appreciated. They have convincingly responded to a majority of the major remarks and to most of the minor ones (although new minor concerns arise), which is a significant step forward toward the publication of their work. However, several major issues previously arosen still remain, which either fragilize some of the authors’ conclusions or complexify the reading. I therefore recommend a major revision of the manuscript.

The following major concerns still remain:

M1 Although the authors disagreed with me on the too large number of Figures, I believe this remark is even truer now that the manuscript reaches 20 Figures. Some of them provide repetitive informations and others are too raw to support the authors’ claims, fragilizing them. The authors should seek to be more synthetic and to add a few (simple) diagnostics to some Figures to be more convincing. In particular:
- I still believe Figures 11 and 12 repeat already-existing informations and the added value of showing statistical distributions is very low as it is presented. Also, as mentioned in former remark m14 (which has not been addressed), I think displaying relative differences (Fig.11c,d and Fig.12d,e,f) is irrelevant: especially for salinity, it gives the misleading impression that the bias is low and it makes it hard to read the actual salinity bias. As mentioned in the previous m14, absolute differences would be easier to read and interpret. For the q-q plots (Fig.11a,b and Fig.12a,b,c), the dashed-dotted line is still not labelled, please explain how it is obtained.
- As mentioned in the previous review, model-obs Figures could easily be merged with obs-only Figures, which would make the reading much simpler. The authors have already successfully done it for Figure 6, they could do the same by removing Figures 9 and 10 and putting them aside their observational counterparts.
- As already mentioned before, Figure 15 is not insightful as it is now and could also be removed. The SI difference doesn’t read well and plotting directly both time differences would have been easier, and most of the domain already has a very low (<0.05m²/s²) stratification before the Bora events occur. Also, diaplaying the MLD would be very insightful (see comment M3).
- The new Table 2 is too instantaneous to be insightful and could also be removed. Instead, the intense transports during Bora events could be compared in the text to the winter mean transport (e.g. on average during the 6 Bora events, the T, S and volume transports are respectively X times, Y times and Z times larger than their winter mean value). Also, mass and volume transports are almost identical so that the mass transport could be removed from Table 1.
- The very large number of geographic locations makes the reading very confusing. In particular, the following locations should appear in Figure 1: Istria, Sedmovrace, Senj, Kvarneric (confusion between A4, T4 and Kvarneric transect).

M3 Although the authors have put forward more explicitely both hypotheses of a DWF occurring locally or dense waters from the open Adriatic shelf, I still find the conclusions confusing, including those stated in the abstract. In addition, as in coastal areas DWF occurs exclusively when the mixed layer reaches the bottom of the water column, the lack of any mixed layer computation is still a major drawback of the paper.
- Regarding the first point, here is the conclusion I have reached, which is clearly stated nowhere in the paper : « Observations at transect T4 and station A9 show the incoming of dense water from the open shelf, and current profiles only show marginal outward transport of dense water from the NADEX area to the open shelf. They support balanced inward-outward dense water exchanges or even a dominating inward transport. However, modelling results show the domination of outward dense water transport, strongly supporting the hypothesis that the NADEX area is a source of dense waters for the open Adriatic. » Please re-formulate more clearly the respective contributions of the local formation, outward and inward transport in the NADEX area to the DWF phenomenon, in particular in the abstract, the conclusion and section 4 (p.9, L.4-25).
- Regarding the lack of any mixed layer computation: I believe that comments of Figure 13 are not convincing without an MLD being displayed (see also comments m9 and m11), and the color range change obviously didn’t fix the issue (it is still impossible to read with the eye a 0.01kg/m³ density variation). I also believe (former M8) that Figure 15 should be removed if no mixed layer is displayed (eg: relevant contours). Figure 15 would be insightful if the IS time difference map was displayed together with a relevant MLD contour (e.g. 50m depth) before and after the Bora event, so that the reader can objectively identify the regions of DWF created by the Bora event.

M11 (new) The authors claim in their response to have addressed their general question 4 (What are the associated mesoscale and frontal processes associated?), which I believe is not the case: no actual mesoscale or frontal process has been studied, they have just identified a front. As questions 1 to 3 are enough, I believe question 4 should be removed.

Here is a list of the new minor concern :

m1 The authors have identified an interesting bottom hydrological trend in observations which is the main signature of DWF: they should evaluate it in the model.

m2 p.6, L.15 Compare year 2015 to the 10-year average rather than to specific years, because the fact that it is lower than 2012 and higher than 2014 doesn’t prove that year 2015 was average.

m3 p.7 L.27 How do you know that this incoming occurred dominantly through T4 connecting passage ?

m4 p.9, L.4-5 Question 2 is not answered to in the whole manuscript (see comment M3).

m5 p.8, L.28 Fig.5 not Fig6.

m6 p.9, L.5 Fig.6 not Fig7. The orientation of all channel cross-sections would help a lot to interpret Fig.6 as each section has a different orientation (e.g. just display for instance a horizontal line on top of the current measurements if the section is East-West).

m7 p.10, L.15-16 Positive bias, not negative.

m8 p.11, L.11-21 The model evaluation is too qualitative, be more quantitative (e.g. bias in the module and in the angle). For now it is not convincing that the model performs overall well.

m9 p.11, L30 The water column was not homogeneous all the time from December to early April. Only displaying the MLD in Fig.13 would determine when it occurred (when the MLD reached the bottom). For instance, it is clear that DWF was intermittent in early January and in March.

m10 p.12 L.3 Also (maybe mostly) the surface radiative forcing restratifies the water column.

m11 p.12, L.3-5 I don’t agree on the comparison between G1 and G2: the water column looks much more homogeneous throughout the winter in G2 than G1. Once again, displaying the MLD would determine if it is the case or not.

m12 p.13 L.14 Why do you expect wind-driven dynamics to induce an energy loss?

m13 p.14 In the formula, rename U vector as Uout for instance to specify that it is only the outward velocity.

m14 p.14 L.13-25 There are a series of English and typing mistakes, please correct them.

m15 Use the same range of values between Fig.17 and 19.

m16 p.17 paragraph 1 Also, the lateral boundary conditions for momentum impact highly the level of kinetic energy close to the coastline. Do you have free-slip conditions? If not, this would be a means of improving the modelled velocities in the NADEX area.

m17 p.17 L.15 Don’t talk about one-way coupling: it is just a forced atmospheric simulation.

m18 A schematic scheme of the main phenomena evidenced in this field campaign would help the reader to have a general overview of the main results of the study.

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ED: Reconsider after major revisions (31 Aug 2017) by Simon Josey

AR by Ivica Vilibić on behalf of the Authors (30 Sep 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Oct 2017) by Simon Josey

RR by Anonymous Referee #1 (07 Nov 2017)

Suggestions for revision or reasons for rejection

This is the third review of the manuscript « Dense water formation in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment » by Vilibic et al. The authors have provided again a detailed response to the previous comments, in particular to all major concerns. I therefore recommend a minor review, addressing however a series of general and particular issues.

General remarks:
- In general, please think of a reader who doesn’t know the geography of the region and who doesn’t know by heart the location in time/space of all measurements. Try to help the reader to easily follow the results in time and space.
- The results sections are still very descriptive, and I think that a summary at the end of each section of the main conclusions would help the reader to make a synthesis. One often ends a section with an accumulation of descriptive informations, but with no general and synthetic overview of the main results.

Particular remarks:
p2 L33 hurricane magnitudes
p3 L9 advected, or being advected
p3 L11 was not considered
p4 L3 Senj. These inputs
p4 L5 many submarine
Figure 3 and 5: the observation and model plots could be harmonized to ease the reading.
p8 L20 which statistical significance test?
p8 L24 does the Figure display twice approximately the same track? If it is the case, give in abscissa the geographic location along the track (longitude and/or latitude)
p9 L20 no inflow is visible at the bottom of station A9
Figure 7: why is a significant fraction of the transport along-channel and not across-channel in stations A8 and A9? Are the current measurements located within each channel or outside them?
p10 L9: the temperature overestimation close to the coast (stations 15 to 19) has not been commented. How does it relate to the salinity bias?
p10 L14: (Fig.8b).
p10 L16: (15-35m, Fig.8a).
p10 L21-31:
- a geographic indication (longitude and/or latitude) is necessary in the abscissa for the reader to follow the text.
- you mention an increase in negative bias although we see in both Figures an overall positive bias: is the model bias (model minus observations) displayed? In which case what increase of negative bias are you referring to?
- the colorbar saturates in Figure 5b: please widen the range of values so that the reader can identify the magnitude of the bias.
p11 L1: for the 3rd time, please explain how you compute the dashed-dotted lines: you mention in the legend that it is the « Q-Q slope of a particular dataset », but how do you determine it? For instance, why does the light blue line in Figure 9b have a much larger slope than the light blue dots? It does not seem to be a least square fit.
Figure 10: the previous colorbar was fine, the problem was the absence of any MLD computation. I think the current colorbar reads worse and you should use the previous one.
p12 L13: the De Boyer Montegut, GRL 2004’s density threshold of 0.125kg/m³ is not adapted to the Mediterranean Sea due to the low stratification in this basin, especially in DWF areas. This is why using this criterion, D’Ortenzio et al, GRL 2005 were unable to successfully identify the main Mediterranean DWF areas with this criterion (their Figure 1, months January to March). The usual threshold is DT=0.1°C or Drho=0.02kg/m³ (Houpert et al, PiO 2015, Somot et al, CD 2016), which allowed for instance Houpert et al, PiO 2015 to identify the main Mediterranean DWF areas (their Figure 7).
p12 L25 and last paragraph of 6.1: Figure 12 and Figure 11 seem to have been reversed. Please display first the first Figure that is commented in the text.
p13 L12: they are surface buoyancy fluxes, not buoyancy changes. Also, in Figure 11 (not 12), it is daily integral values (in m²/s²), not daily values (in m²/s³), which are displayed.
p14 L5 what do you mean by « constructions »?
p15 L2: Uout (the outward velocity) is already U.n (the total velocity projected onto the outter normal unit vector), so that you can replace Uout.n simply by Uout in the formula.
p15 L5: there is no need to assume no incoming water, but simply that the incoming flux is equal to the outcoming one, which is reasonable over long timescales because otherwise the sea level would vary a lot.
p16, L.6: it is not a coupled atmosphere-ocean model because there is no feedback between both models. It is a nested oceanic model which is forced by an assimilated atmospheric model.
p16, L.10: I have not understood your conclusion (ii).
p16, L25: why do you cite a 2006 paper to comment on the excitation of the thermohaline circulation in the 2015 event? Orlic et al 2006 seem inappropriate here.

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RR by Anonymous Referee #2 (29 Nov 2017)

Suggestions for revision or reasons for rejection

Review of Manuscript “Dense water formation in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment” by Vilibic et al.
General comment to the Authors and the Editor:
With respect to the previous version, I must admit that now the discussion of data and model results is much clearer, and most of the confusion I found in the previous versions of the paper has been eliminated. Also English has much improved and I want to give credit to the authors for this big effort.
However, and I am sorry that I might be repetitive….in my opinion the paper does not answer the questions it poses at the beginning. And this, to me, is now much clearer as the paper structure is much clearer. Most of the discussion is not even related with DWF. So I only have one advise, otherwise I cannot accept the paper: the title must be changed and the objectives. Other parts of the paper might undergo to some change accordingly. I know it is an incisive change, but this paper gives a nice and comprehensive description of the dynamics in the northeastern Adriatic area, and as such it deserves publication. But it is NOT a paper about DWF. The authors might write that they performed the experiment in an area that might be important for DWF, as shown by other studies, but not that this paper describes the DWF and how common it is in this area (with just one experiment, it is rather strange that you claim to be able to say how common DWF is).
Some more detailed comments are:
- Page 4, Line 18: you should rephrase here since it seems that RDI ADCPS were used also in A1-A3 and A5-A6. Please specify the depths of these stations as well and the depth of the SBE probes closed to the ADCPs.
- Page 4, Line 25-27: it appears that the cruises were not done in the period of DWF and that only the ARVOR might have “seen” something during the last episode.
- Page 5, Line 19: should be σ-coordinate
- Page 6, Line 10: Vilibic et al., 2016a or 2016b?
- Page 6, Line 13: “warmer than average conditions”
- Page 7, Line24- Page 8 line 26: this description has nothing to do with the objective of describing DWF in the area, it describes data taken in other periods of the year.
- Page 9, Line12-14: this hypothesis is unsupported by the observations.
- Page 9, Line 20-21: I cannot see this inflow in fig. 7 at A9….
- Page 9, line 15-16: showing a two months average of the circulation (fig. 7) is not that much significant in a coastal area where a lot of mesoscale features are expected and is therefore not useful to describe outflowing dense waters.
- Fig. 7 does not show the scale of velocities
- Caption of Figure 8 needs a more detailed description
-
- Page 10, line 20: the fact that the modelled PDA during leg 2(which is in May) was higher that the observed PDA in December, is not at all demonstrating that the model was able to reproduce DWF in the Nadex area.
- Page 12, line14: you are saying that what you observe in one point, G2, is telling you something about “most of the basin”? (again stated at line 21….)
- Page 13, line23: you don’t say anything on how these fluxes have been computed…with the model? And if yes, why in these locations if no comparison with data-based flux computation is done?
- Page 16, line 1: “into the processes”….which ones?
- Page 16, line 6-7: your dataset is not able to answer to question (i)
- Page 16, line 9: the CTD data were collected in December and in may, so they cannot show you that DWF did occur in the nadex area
- Page 16, line 12: the dense water is transported outward at the Surface layer?
- Fig. 6: would be useful to indicate on the plots wher is east and where west
- Caption figure 9: what is the black line?
- Figure 10: use the same colorbar as in fig- 3
- Caption fig. 17: should be “of total (TRT) and dense water (DWRT)”

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ED: Reconsider after major revisions (18 Dec 2017) by Simon Josey

AR by Ivica Vilibić on behalf of the Authors (12 Jan 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Jan 2018) by Simon Josey

RR by Anonymous Referee #1 (29 Jan 2018)

Suggestions for revision or reasons for rejection

This is the fourth review of the manuscript « Dense water formation in the coastal northeastern Adriatic Sea: the NAdEx 2015 experiment » by Vilibic et al. The authors have once again addressed comprehensively the previous remarks, which is highly appreciated. The manuscript is largely improved, and I therefore recommend a minor revision.

The following minor concerns should however be addressed:
p.2 L.16: I do not believe that only the spatial inhomogeneity of the Bora wind can explain the Adriatic double-gyre circulation. Hendershott and Rizzoli, DSR 1976 also put forward the key roles of:
- the coastal inflow of freshwater to enhance the horizontal density gradient that feeds the cyclonic circulation;
- the ocean bottom topography to force the double cyclonic circulation.
p.6 L.20-21: can you specify which percentiles you are referring to? Is it percentiles of the climatological mean distribution (30-year mean) or only of that particular year?
L.26-28: a cumulative heat loss of 0.80MJ/m²=800,000J/m² over those 2 months is equivalent to a mean heat loss of 800,000/(31+28)/86400=0.16W/m². Therefore I deduce that there is an error of unit that could have been avoided. Is it GJ rather than MJ? It would make it 160W/m², which is the right order of magnitude.
p.8 L.18: continuous rather than constant
p.9 L.3-5: the southeast-northwest differences in T,S are not clearly visible in the PDA series: I would rather say that they are density-compensated. What is mostly visible in PDA time series is the signature of the cooling trend.
p.10 L.5: what do you mean by constrictions?
p.11 L.20: does
p.12 L.1: misrepresented
p.13 L.7: by the heat losses induced by the Bora wind
p.13 L.30: for clarity, you could first comment on the overall negative flux, and then go to the details of individual transects T1, T3, T2 and T789.
p.14 L.2: summing, not averaging
p.14 L.9: I guess 6 and 2 times are for resp. T and S?
p.15 L.14: strictly speaking, you have shown that the coastal NE Adriatic loses dense water volume, not mass. Although I agree that because these dense waters are replaced by lighter incoming waters, it implies that the basin loses mass.
p.17 L.16-19: just a remark to put into perspective the role of the Adriatic SST on Bora events. Stocchi and Davolio, Atmospheric Research 2017 show a very weak impact of air-sea water exchanges over the Adriatic Sea on the atmospheric water budget during Bora events.

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ED: Publish subject to minor revisions (review by editor) (14 Feb 2018) by Simon Josey

AR by Ivica Vilibić on behalf of the Authors (15 Feb 2018) Author's response Manuscript

ED: Publish as is (27 Feb 2018) by Simon Josey

AR by Ivica Vilibić on behalf of the Authors (27 Feb 2018)