Author's Response
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AUTHOR’S RESPONSE Note that all the locations of the changes mentioned herein after correspond to the locations in the “clean” manuscript, not the marked-up version. Anonymous Referee #1 HF radar and coastal altimetry-derived surface currents are quantitatively compared first at certain locations and then along the altimetry ground tracks in the southeastern Bay of Biscay during multiple years from 2009 to 2015. The two data sets are further used to describe the mesoscale dynamics of the Iberian Poleward Current and eddies in the region. It is demonstrated that a combination of different coastal ocean observing systems may provide a better understanding of the coastal ocean processes. Despite the limitations of the ocean observation techniques, the results are encouraging. Also, the topic is interesting and the paper is informative. I would recommend it be accepted for publication after minor revision. Dear reviewer, First of all, thank you for showing the technical errors. They really help to improve the manuscript and we have addressed all of the into the text. Thank you for your specific comments as well. We did not realize that we had not mentioned the confidence level of the correlations, which is 90%. We have also included it as explained below. Best regards, Ivan Manso Comments are enumerated AR = author’s response AC = author’s changes in manuscript 1. Correlation coefficient is used to quantify the comparison between two time series without any statistical significance test. It is important to mention whether a correlation is statistically significant or not, because a high correlation coefficient may not be meaningful at all without a significance test. 1 AR: We considered the significance (90%), therefore, all the results shown in the manuscript are significant. However, it was not mentioned in the text. Thank you for this comment. AC: We have added this information at page 8, line 15 2. “correlation coefficients” are simply written as “correlations” in many cases, which should be clearly specified. AR: We have specified it. AC: Page 8, line 14. 3. Throughout the manuscript, two decimal places are used for ocean current velocities. In my opinion, one decimal digit would be enough. This is because the accuracy of HF radar current measurement is about several cm/s, and the errors in altimetry-derived currents are even larger. AR: We have changed the values, using only one decimal place throughout all the manuscript. 4. Page 1, Line 9, “resolution” should be “resolutions”. AR: Done. AC: Page 1, line 9. 5. Page 1, Line 20, “higher” should be changed to “larger”. AR: The sentence has been rephrased and therefore this adjective has been removed. 6. Page 1, Line 25, “in” should be changed to “by”. AR: Done. AC: Page 1, line 24. 7. Page 2, Lines 1-2, it would be good to refer to a recent book in this topic (Liu et al., 2015). AR: Done. AC: Page 2, line 1. 8. Page 2, Line 17, “resolution” should be “resolutions”. AR: Done. 2 AC: Page 2, line 17. 9. Page 2, Line 17, “of” should be removed. AR: Sorry, but we have not found any ‘of’ in that point. 10. Page 5, Line 6, the single sentence paragraph should be combined with the previous paragraph. AR: We have rephrased and moved this sentence to page 4, line 30. 11. Page 5, Line 14, the single sentence paragraph should be combined with the previous paragraph. AR: Done. AC: Page 5, Line 18. 12. Page 5, Line 23, “except” should be changed to “except for”. AR: Done. AC: Page 5, line 27. 13. Page 7, Line 27, what value is used for Cd? AR: The value we used was the one proposed by Large and Pond (1981) which depends on the velocity of the wind (U10): -3 -1 CD = 1.2 x 10 for 4 < U10 < 11 m s -3 -1 CD = 10 (0.49 + 0.065 U10) for 11 < U10 < 25 m s -3 -1 -3 Note that we have considered 1.2 x 10 for every value smaller than 11 m s and 10 (0.49 + 0.065 U10) for larger values. AC: We have added the reference to Large and Pond (1981) at page 8, line 1. 14. Page 9, Line 28, “the higher is the correlation, the smaller is the difference…” should be changed to “the higher the correlation, the smaller the difference…”. Both “is” should be removed from the sentence. AR: Done. AC: Page 9, line 29. 15. Page 14, Line 27, “Altimetry has also its own limitations” should be changed to Altimetry also has its own limitations”. 3 AR: Done. AC: Page 14, line 30. Anonymous Referee #2 the paper focuses on the validation of two different altimetry products and aims at demonstrating the complementary with high-frequency radar observations of surface currents in the bay of Biscay. the manuscript has a few flaws, that should be accounted for properly before it is accepted for publication. details are given below for the Authors and the Editorial Board. Dear reviewer, Thank you for your thorough reading of the text and the exhaustive review. Your fruitful comments have improved the article. Best regards, Ivan Manso Comments are enumerated AR = author’s response AC = author’s changes in manuscript Abstract: 1. define "surface currents" AR: Done. AC: Page 1, Line 8. 2. correct the spatial and temporal resolution: depending on the HFR system, they can be as low as 300m to 12km, 5 min to 3 hours; same corrections apply within the text. 4 AR: Done. AC: Page 1, Line 9. 3. line 20: what variability is the Author referring to? why is it so? it would be useful to have these details in the abstract AR: The line has been rephrased (see comment 6) and this variability it is not mentioned any more. 4. line 25: is this correlation increase statistically significant? is there a real benefit in including a simplified Ekman current model to the data, given the amount of processing the dataset already go through? AR: Thank you for this comment, the significance of the correlation is 90%, but we forgot to mention it in the text, therefore, it has been added at page 8, line 15. With regard to the addition of the Ekman current model, it is true that the qualitative benefit is not high, but apart from providing a moderate benefit it is methodologically interesting and gives way to a better analysis. 5. check grammar and break sentences to improve readability (mainly within the manuscript) AR: done. 6. lines 20-25: I personally would rephrase this sentence in order to focus on benefits first and limitations after; for instance, something like: "Both HFR and altimetry capture the main oceanographic features in the region (the IPC and the mesoscale eddies), however performances reduce in the areas closer to shore because of ....", or similar. AR: Rephrased. AC: Page 1, Lines 20-24. Introduction: 7. page2, line4: references to Jerico and Jerico-Next should be added AR: Done. AC: Page 2, Line 2. 8. page2, line6: cit: "...best possible quality indicators..." of what? AR: This sentence has been rephrased. 5 AC: Page 2, Line 6. 9. page2, line19: definition of "HF" is missing; the guess is, it means High-Frequency spectral components, but it confuses with the acronym HFR AR: Changed to high-frequency. AC: Page 2, Line 19. 10. page2, line20: HFR do not measure "inertial waves" but can resolve "inertial currents" if the proper grid resolution is set up AR: Thank you, it was a mistake. It has been corrected. AC: Page 2, Line 20. 11. page3, line 12: missing network after HFR AR: Done. AC: Page 3, Line 11. 12. page3, line 15-18: one of the major motivations of this present work - that is, the comparison of the two products - is not stressed out properly in my opinion; this is actually te added value to this manuscript. AR: Rephrased. AC: Page 2, Lines 17-19. Section 2.1.1 13. radial velocities are not measured directly; they are derived from the inversion of the 1st order scatter from Bragg- matching waves AR: We have changed ‘measure’ to ‘infer’. AC: Page 3, Line 24. 14. operational range is usually frequency and bandwidth dependent; low-frequency systems have usually narrower bandwidths thus boosting range but with inversely-proportional range resolution - 40KHz bandwidth should provide a radial range resolution of _3.7km, not 5km as stated. AR: It is true; however, the range cell and angular resolutions are set to 5 km and 5º respectively. 6 AC: We have added this clarification in page 3, line 31. 15. "noise to signal ratio" should be the opposite: signal to noise ratio. AR: Done. AC: Page 4, Line 1. 16. is it the RT HFR product being used, or the reprocessed DM data set used instead? AR: The DM one. 17. "receipt antenna pattern" should be "receive antenna pattern" AR: Done. AC: Page 4, Line 2. 18. bi-annual calibration: performed every two years, or twice per year? AR: It has been performed at least every two years. AC: We have clarified it at page 4, line 2. 19. Page 4, lines 5-13: this section is confusing. Gurgel (1994) and Lipa and Barrick (1983) proposed the unweighted least-square fit for the WERA and the Codar systems. The first does a 1-1 match of radials from two stations, the second uses a spatial search radius. The OMA analysis has nothing to do with this. OMA was developed by Kaplan and Lekien (2007). My understanding is the following: radials in polar coordinate systems from the two separate stations were mapped to currents on a cartesian grid using the HFR_Progs Matlab package; then, an OMA analysis was performed for gap-filling purposes.