Wave Climate Variability along the Coastlines of Senegal over the Last Four Decades

Round 1

Reviewer 1 Report

Review comments on “Wave climate variability along the coastlines of senegal over the last  4 decades”

 

The authors investigated wave climates along the coastal zone of Senegal based on a new high-resolution hindcast covering the period 1980-2021, and evaluated the average, seasonal and extreme values for the wave significant heights (Hs), periods (Tm02/Tp) and mean directions (DIR). It is demonstrated that the wave climate is dominated by swells coming from the North-Atlantic lows during boreal Winter, and the Southern Coast (from Dakar to Casamance) is exposed to swells generated in the South-Atlantic Ocean during boreal Summer. The trends in heights, periods, and mean directions can be explained by the main climate modes of the 27 Atlantic Ocean (NAO/EA during Winter, SAM during Summer). The authors did an excellent analysis; however, some improvements are needed to get the paper published.

 

Major comments:

1)    In figure 2, model sometimes overestimate the mean wave periods and pic periods, what causes that? What’s the dynamic/physical mechanism behind that?

2)    In Figure 4, the extreme wave pattern seems similar to the annual mean (Fig. 3), what’s the mechanism behand that?

3)    In Figure 5, the wave pattern in Summer is very different from other seasons for DIR and Tp, how to explain that?

4)    In Figure 7, what causes those trends?

5)    NAO seems have strong impact on wave variation; how about ENSO (el nino and southern oscillation)

 

 

Minor comments:

1)    Don’t write title in all uppercase.

2)    In line 19, DIR is used to refer direction; however, in line 44, Dir is used to refer direction. Please unify it.

3)    Line 587, “2022” to “(2022)”

4)    Line 592, “2022” to “(2022)”

The paper is well written.

Author Response

Firstly, we would like to thank sincerely the reviewer for his detailed review, which allowed us to clarify several points in the revised manuscript, which makes it more robust.

We responded directly to the reviewer in an attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article investigates the wave climate along the coast of Senegal, focusing on the climate fields of the average wave parameters and their possible connection with global atmospheric circulation. There are some comments and questions regarding the analysis and interpretation of the results:

1. The analysis focuses on four parameters: significant wave height, mean period Tmo2, spectrum peak period, and wave direction. The climatic fields are obtained by averaging the calculated fields.

The use of two periods is questionable. There is a good regression between the peak periods and the mean periods.

The averaging of the wave directions is unclear since it can produce misleading results. When directions in adjacent periods have values of 350 and 10 degrees, which are the same north direction, averaging gives a south direction with an average value of 180 degrees. Vector components should be averaged instead.

2. The lack of local bathymetry, which is specific to the Senegal coast, is evident in Figure 1:

This does not make it possible to estimate very significant local features that are present here. These can be assessed using the Navionics navigation resource map that highlights in blue the depth at less than 20 meters:

The map shows an abrupt continental slope north of Dakar and an extensive shoal to the south, which are relevant to the study.

3. The simulation results are compared with records from the NORTEK AWAC profiler at a depth of 35 m. It is important to know its operation frequency because the authors point out that «orbital wave motions were too much damped by 35 m water depth to compute directional wave spectra and the analysis was therefore restricted to 1D frequency spectra». Registration of orbital velocities and calculation of two-dimensional spectra are possible at this depth. Therefore, their absence in the analysis is questionable.

4. Line 189. The authors write, «PSDs were integrated between a low frequency cutoff F_min set as half of the peak frequency and a high frequency cutoff set at 0.15 Hz». In other words, an interval of 6.7 s to about 30 s is considered. It remains unclear what is the reason for this choice.

This point can be seen in Figure 2:

The choice of periods of less than 6.7 s in 2019 and about 7.5 s in 2020 suggests uncertainty and a lack of elaboration in the selection process.

5. The decision to consider the 90th, 99th, and 100th percentiles as extreme characteristics is questionable. Usually the 99th percentile is sufficient, and the 100th percentile can be an outlier.

6. A small error is identified in Figures 3 and 4, where Pic period should be replaced with Peak period.

7. Relation of the wave fields to the atmospheric circulation indices.

The principle of selection of indices, among which are North Atlantic Oscillation (NAO), East Atlantic Mode (EA), and Southern Annular Mode (SAM), is unclear. The structural similarity of EA and NAO makes their simultaneous use superfluous. The choice of SAM, which is determined on the basis of pressure variations in the middle and high latitudes of the Southern Hemisphere, is also questionable.

There are a large number of circulation indices. Due to their global nature, correlations with the same wave heights are possible anywhere in the ocean. In other words, correlations can be found anywhere.

The study lacks a rationale for the selection of the indices, and an interpretation of the results. This seems understandable because it is difficult to explain how directions can be correlated.

Further, indices are integral concepts. As a rule, daily values are provided. Average daily calculation series should have been formed, however the authors do not give any information on this.

Furthermore, the interpretation of the results leads to contradictory conclusions. In line 475 we read: «The spatial distribution for all the wave parameters showed a significant contrast between the Big and the Small coasts on the mean, seasonal and even in the extreme wave climate conditions». (Recall that the Big Coast and the Small Coast are separated by the Dakar Peninsula). However, regarding the interaction with NAO, we read in line 348: «H_s and NAO are strongly negatively correlated with values of -0.6 on the ‘Big coast’ and up to -0.7 on the ‘Small coast’», i.e. the correlations are almost identical. Obviously, the significant contrast in wave climates is due to other causes. The lack of an explanation for these contradictions remains a serious gap in the interpretation of the study results.

Conclusions.

1. Overall, the article is lacking attention to detail in its formatting, including inconsistent subheading numbering between ’3.1. Wavewatch’ and ’III-2 Forcing Fields,’ as well as a table (Table 7) that is referenced multiple times but not included in the text.:

2. Additionally, the article mentions results that are "not shown here" three times (lines 232, 391, and 424). It is unclear why these results are mentioned if they are not included.

3. The article looks like a compilation of other papers and reports rather than presenting a holistic concept. The only results presented are fields of significant wave heights and periods, but it is evident that swell is a key aspect. It would be useful to pay attention to the two-dimensional spectra computed by the WaveWatch model, as they give complete information on wave field composition and directions. It would also be useful to involve satellite data to verify the model.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Firstly, we would like to thank sincerely the reviewer for his detailed review, which allowed us to clarify several points in the revised manuscript, which makes it more robust.

We responded directly in an attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper is well-written, the objectives are clear, and the methods employed are appropriate. However, the document does not clearly highlight the scientific contribution that the authors make in the current state of the art. The analysis of climate variability in the coastal zone of Senegal is good, and the conclusions are of scientific interest. However, there is no in-depth discussion about why the creation of a new hindcast is relevant. The authors state in their introduction that hindcasts have already been carried out by other authors, which, I understand, would allow for a similar climate analysis to the one presented. In other words, it is not clear why there is a need to create a new hindcast. Furthermore, this hindcast is created using the WW3 model, just like the existing databases. It is true that the authors indicate that they have done it using an improved wind forcing, but is this enough to justify a new hindcast? On the other hand, if the intention is to present a coastal-level analysis, wouldn't it be sufficient to use the WW3 model and perhaps require a more detailed downscaling with a model like SWAN to capture the relevant wave propagation phenomena on the coast? Therefore, I believe that the paper needs to be much clearer about what is gained with the new hindcast created and whether this hindcast is sufficient to reach the required coastal-level conclusions in this region of the world. It should also clearly justify why the databases of other authors in this region of the world have not been used (perhaps by directly comparing the data). In summary, I consider that the article needs to undergo MAJOR REVISIONS in this regard.

Author Response

Dear Reviewer,

Firstly, we would like to thank sincerely the reviewer for his detailed review, which allowed us to clarify several points in the revised manuscript, which makes it more robust.

We responded directly to the reviewer in an attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thanks, a lot of work has been done.

Reviewer 3 Report

After second round, the paper should be accepted in it's present form.