Investigation of Air-Sea Turbulent Momentum Flux over the Aegean Sea with a Wind-Wave Coupling Model

Round 1

Reviewer 1 Report

A well written paper. The physical shortcomings are outlined by the authors. Just a suggestion:

Lines 424-427: the concept is not clear, it should be better explained.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript “Investigation of air-sea fluxes over the Aegean Sea with a 2 wind-wave coupling model” by Portolakis et al. compares momentum and heat exchange estimates over the Aegean Sea derived from two different models and compares them with the momentum and heat flux estimates calculated from airborne measurements collected during several flight campaigns over the Aegean Sea in 2011. The main focus of the manuscript is the test of the applicability of the both models for the Aegean Sea, which may display different interactions between the wind and wave field compared to the open ocean as it is a semi-enclosed basin with numerous islands that disturb the wind and wave fields.

This work is a valuable contribution to improve the understanding and predictability of the atmosphere-ocean interactions over the ocean. Since the exchange of heat and momentum is an important driver of the physical processes in the ocean, improvements in the simulations of these parameters can significantly improve the general representation of the physics in the ocean. Testing the applicability and the potential limitations of the flux parameterizations for the Aegean Sea, which may display different interactions between the wind and wave field compared to the open ocean, can enable more precise predictions of oceanic and atmospheric exchange processes.

The authors found a reasonably good agreement between the fluxes derived from airborne measurements and the model-derived fluxes, and the discussion of the results is detailed, understandable and supports the conclusions drawn by the authors. The authors also include a discussion of the limitations of the comparison between field measurements and model output.

The manuscript is generally well structured and the overall readability is fair, but additional language editing may further improve the manuscript, as some formulations seem rather imprecise, and the authors need to take care that the reader can unambiguously understand their formulations (see some of my specific comments below). A more precise formulation of the exact parameters that were determined by the authors (e.g. instead of writing “flux” only, the authors should mention that momentum and heat flux were determined) is needed.

Specific comments:

General: the authors should check the tenses used in their results section since observational results should be reported in past tense, not present tense (see e.g. line 371, 380 and others).

Line 91 and others: the authors should specify which kind of fluxes are evaluated in the manuscript. The term “air-sea fluxes” is somewhat ambiguous, and for the reader it is not clear from the beginning which physical parameters are investigated in detail.

Line 161: “The parameterisation of the Charnock coefficient as a […]”

Lines 177-183: it is not clear to me, which kind of field measurements exactly were carried out and used for the work presented in the manuscript. The authors should add some more information on the instruments used and the exact parameters which were determined from these instruments.

Line 180: the abbreviation PBL needs to be defined here, not in line 236.

Line 196: this was set to 250 m

Line 201: atmospheric stability?

Line 202: See my comment on lines 177-183. The authors should further specify which exact parameters were obtained from the buoys network.

Line 210: The AS is a… [without comma]

Lines 211- 212: “Due to the […] strongly influenced” - The exact meaning of this sentence is not clear to me. The formulation of the sentence sounds somewhat strange. Does this mean that the wind and wave field are influenced by the complex topography, leading to large spatial and temporal variability of winds and waves?

Lines 214-215: ...the meteorological conditions during the AG campaigns were representative for an Etesian wind outbreak…

Line 215: “persistant northerly flow” - replace “flow” by “wind”

Lines 218-219: where did the authors obtain the SST, air temperature and wind speed data from?

Line 291: The wave conditions […] were determined by...

Line 360: what is meant by the term “aircraft fluxes”? Momentum and heat flux estimated from airborne measurements?

Line 363: ...that do not allow for equilibrium conditions and longer averaging…

- The combination of “equilibrium conditions” and “longer averaging” in this sentence sounds somewhat strange – in the first case, a physical condition is described and in the second case, a statistical methodology.

Line 364: ...distance to the upwind shoreline…

Line 419: “The fluxes variability on the mean flow parameters” - I do not exactly understand what is meant by “mean flow parameters” here. Can the authors specify which parameters were investigated?

Line 450: “a linear with height flux divergence” - this formulation sounds a bit odd. Maybe the authors could rephrase it to something like: “a linear relationship between height and flux divergence”

Line 520: under these conditions

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Review of the manuscript "Investigation of air-sea fluxes over the Aegean Sea with a wind-wave coupling model" by Portalakis et al. (manuscript # 'atmosphere-1329184')

General Assessment:

The study by Portalakis et al. investigates surface stress (momentum flux) over the Aegean Sea using two different theoretical approaches: 1) the wind-wave coupling model by Kudryavtsev-Chapron-Makin (KCM) and 2) the version 3.5 of the Coupled Ocean-Atmosphere Response Experiment (COARE) bulk algorithm by Fairall et al. (1996, 2003) and Edson et al. (2013). The KCM spectral input is provided by the SWAN model, which is driven by the WRF model. In addition, airborne measurements of the momentum flux (at ~150 m above sea surface) were compared with the models simulations.

Judgement:

I found the paper quite interesting and original and the use of two air-sea flux algorithms and airborne measurements is particularly informative. This paper includes a lot of information. I also think that the exercise has an obvious practical value. I recommend acceptance with major revisions although most of the comments are not that major and related to lack of clarity. I also note cases where the paper could be made more concise.

Specific comments:

My main concern about the paper is lack of discussion on the height-corrected airborne measured momentum flux (from ~ 150m down to ~ 10 m). Although it is appropriate to refer readers to other papers [31, 49, 50] for the details of the height-corrected friction velocity, more info is needed in this paper than is currently provided. In particular, authors need more discussion on the possible causes of discrepancies between models and observed height-corrected friction velocity in Figure 8a. I cannot find much relevant information beyond reference to Smedman et al. paper [78]. It is possible that a different interpolation is needed in this case than a linear height-correction method. I think that discussion of these points can strengthen author's findings.

One could also recommend changing the title a bit: "Investigation of surface stress over the Aegean Sea with two air-sea flux algorithms and airborne measurements". First, the study focuses only on the momentum flux and not on all three air-sea fluxes (i.e., plus the sensible and latent heat fluxes). Second, the paper considers two models (KCM & COARE) and airborne measurements, that is, not only "a wind-wave coupling model" (KCM?). It is quite possible that I am missing something and a clarification would help.

Lines 91 and 112. Replace the "the air-sea fluxes" with "momentum flux" (see my comment on the title above). Also, replace "turbulent fluxes" with "momentum flux" in the text (e.g., in the abstract, keywords, and on lines 183, 478 etc.)

There are too many abbreviations in the paper. It sometimes is overwhelming for the readers. Acronyms should not be used unless absolutely necessary. In addition, the abstract should not contain any undefined abbreviations.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The authors have responded to my previous issues and the paper can be accepted in my opinion. No further comments to authors, and I don't need to review the manuscript again.