The Impact of Tides on the Bay of Biscay Dynamics

Round 1

Reviewer 1 Report

Point 1: In the introduction section, a few more up-to-date references could be added and discussed.

Point 2: Figure 2, 3, 4 and 5. Please add labels for x-axis, y-axis, and colorbar

Point 3: Line 92-99: This part is the model result. It would be better to be moved to Results section.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents the results from a 3D hydrodynamic ocean model's twin experiment 1) with 2) without the tides. The paper is very informative. Good review and well written. Here is a few comments regarding the paper.

1) In line 22-23, authors stated that “There are two common approaches to include tides in the ocean model simulations: either with direct simulation or parameterization”. Could authors specifically address the parameterization process to include the tides (for example bottom friction coefficient, etc. …)? How to do it? Especially in this prefect occasion of twin experiment?

2) In the twin experiment, it seems there is lack of observed data to quantify/qualify the advantage of including the tides or vice versa. Could authors address question of observed data and reason why lack of it?

3) Please check the figure caption of Figure 6.

Author Response

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Reviewer 3 Report

In this manuscript, the authors qualitatively assess the effects of tides on the temperature and salinity distributions in the Bay of Biscay through a comparison of two numerical experiments with and without tidal forcing. The manuscript is written plainly overall. However, it is not clear what kind of physical processes the authors are specifically interested in. Furthermore, the authors do not provide a deep insight into the dynamics responsible for the change brought about by the introduction of tides. As a result, the manuscript reads more like a technical report. I would therefore recommend that the authors resubmit the manuscript after major revision with more emphasis on the physics behind the computed results.

Below are some examples of physical processes which could be pursued in more detail:

- The authors found that a strong SST front (Ushant front) is realistically reproduced only when tides are included in the numerical model. This may be an interesting result, but the authors do not at all examine why the front is created there and how it is maintained. The authors can, for example, examine the vertical cross-section of model-predicted vertical diffusivity, temperature, and circulation pattern to show the dynamical balance working at the front. They can also examine the so-called "Simpson and Hunter (1974) parameter" in terms of which the location of a tidal front is often discussed.

- The authors mention several times the importance of internal tides on the temperature and salinity distributions in the Bay of Biscay. They then need to examine more quantitatively where the internal tides are generated, how they propagate, and where they are finally dissipated to cause turbulent mixing. This can be achieved (at least partially) by carrying out a basic energetic analysis for both the barotropic and baroclinic fields.

- The authors seem to suggest that internal tides interact with meso- and small-scale eddies in the open-ocean. This may be an interesting result, but if the authors want to emphasize this finding, they should clarify the physical mechanism of this interaction. For example, the eddy energy is most significantly enhanced at the wavelength of ~70–80 km through the interaction with internal tides (Figure 10b). Also, the meaoscale eddy activity is enhanced (suppressed) in the open-ocean (on the shelves) (Lines 202–204). Why are these?

Below are other specific comments:

- Line 83: The vertical mixing scheme employed in the model should be briefly explained for both the bottom boundary layer and the interior ocean since vertical mixing is a key process in this study.

- Section 2.2: Is the tidal motion induced only by open boundary conditions, or also by the tidal potential?

- Lines 165–167: More clear evidence is needed showing that this difference in the SST field is caused by the frontal displacement of river plumes.

- Lines 168–170: How do internal tides cause SST cooling in this area? Are they breaking there?

- Lines 173–175: In general, the SSS change can be caused either by "vertical mixing" or "horizontal advection". Although the authors seem to insist that the latter is more important, this is not demonstrated clearly.

- Section 3.2: Why do the authors examine relative vorticity rather than, for example, horizontal divergence in which internal tides are expected to appear more clearly?

- Lines 261–263: This sentence does not seem to be consistent with the sentence just below (Lines 264–266).

- Lines 263–264, "most likely because of ...": I do not understand what the authors are trying to say here.

- Lines 273–275: How can tidal "mixing" cause the SSH variability?

- Line 320–322: This statement appears to be inconsistent with Figure 10b.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have responded to most of my comments by not giving deep insights into the dynamics, but simply noting that they are future works. This makes me wonder whether the manuscript is significantly improved. Nevertheless, the revised manuscript is overall sound and clearly written, so I think that the manuscript may be acceptable for the journal.