Dear authors.
Thank-you for your revised manuscript. Unfortunately I think it is not ready to go back to reviewers, which will be necessary before publication.
The most serious comments are: lack of clear objectives beyond describing the observations, a point made by both reviewers – this should be at the end of the Introduction; the manuscript (pages 3, 4) does not answer reviewer 2 point 2 wanting better explanation of methods; you do not explain what you mean by WPD or describe it; there is description but very little dynamical interpretation which was wanted by the reviewers.

Here follow detailed comments intended to improve clarity. Page and line numbers refer to the “clean” version of the revised manuscript.

Page 1
Line 15. “. . the monsoon is strong enough to change . .”
Line 16. Omit “which”
Line 17. “. . into a meridional current. . “
Line 22. “. . main water masses . . are understood . .” is not very sensible. It might mean that we understand how these water masses are formed but you do not say anything about that. Perhaps “. . main water masses . . have been described . .” ?

Page 2
ines 4-5. I do not understand “feasibility of the ocean ventilation theory is still unknown for the northern IO”. Maybe “feasibility” -> “applicability”? In any case you should explain why there is this uncertainty – why should the limited (but still large) meridional extent of the Indian Ocean negate ventilation theory?
Line 5. Be explicit: what are the “other two basins”?
Line 6. So there is a contrast between the two ideas. Which corresponds with observations? Or is it an aim of the manuscript to answer this through observations?
Line 9. “close to the tropic” – unclear, use your revised definitions.
Lines 11-12. “ Rossby wave, . . . and west-propagating disturbance”. What is the difference? Or definition of west-propagating disturbance? Rossby waves propagate westwards.
Lines 15-16. “interdisciplinary survey” (spellings).
Line 16. “and the CTD and XCTD station data have not yet been explored.” You cannot say this because you use them in this manuscript. You could say (earlier, if true) that previous CTD and XCTD data are lacking.
Lines 17-22. These aims are still very unclear and mostly not attempted in the manuscript.
Line 19. “this analysis provides a reference to the basic energy theory” is especially unclear.

Page 3 line 4. 47.17km is quite a large separation, comparable with an internal deformation radius (eddy or internal wave scale). Line 9. 79.97 km – same comment. How do you use these comparisons (XCTD versus CTD; XCTD versus Argo) to calibrate* or estimate uncertainties in which instrument readings? *According to your response to reviewer 2 you did not calibrate the readings but the manuscript needs to be explicit about this.

Page 4 bottom lines. “We later use objective analysis method and low-pass filter to reduce the differences among CTD, XCTD and Argo.” is very unclear. Differences between the values from various measurement methods are unalterable facts and cannot be reduced.

Page 5
Line 8. “with a uniform 100 km interval in the y-coordinate” is unclear. Does this mean data located over a y-range 100 km are all merged? 100 km seems a very coarse grid spacing. Some features in figure 2 have scales smaller than this.
Lines 9-14. What about time? Are all data from the month merged to one description? If so, you cannot refer to west-propagating disturbance because you cannot “see” propagation.

Page 6
Line 5. “. . observations.”
Line 12. Omit “interval of”
Line 16. “. . starts . . ends . .”
Lines 17-18. You can omit “which is preferentially defined as the later stage of monsoon transition,”
Line 19-20. “Positive wind curl . . . induces sufficient coastal upwelling”. Maybe. But the upwelling is strongest at the coast which suggests that the wind stress at the coast is the main cause; it drives off-coast Ekman water transport. In fact positive wind (stress) curl drives upwelling, not exactly off-coast transport.
Line 22. You can omit “dominant”.
Lines 23-24. Better “. . annual mean, and forces downwelling. The basin-scale . .”
Line 24. “front”? The changes are over 100s km, is this scale small enough to be called a ”front”?

Page 7, bottom lines. “. . propagating . . (WPD). . .” Your response refers to Maximenko et al. (2005). You should cite it here. How do you tell that the WPD is propagating? I agree that the westward current at 6°N is exceptional for its zonal extent, but not for its magnitude: there are several other places in figure 2c where the arrows indicate currents of order 0.4 m/s.

Page 8
Lines 15-16. “some isothermal lines rise to the surface on the northern side and show a clear ventilation structure”. “some” = “one” and this is not sufficient to show the temperature range of what rises to the surface. This might all be mixed layer by the definition in your response. Therefore not “clear”.
Line 25. “on the activities” -> “for the distributions”
Lines 26, 27. “. . in both the snapshot and climatology.” And in SODA and HYCOM?
Lines 27-30. How are these sentences related to each other? What about 21.9 or 22.1 kg/m3 outcrops?
Line 33. “. . y=400 km where it crops out. . .” What does “it” refer to? I think cooler sub-surface water but this needs to be explicit because it was not mentioned immediately before.
Line 33. Not “steeply”; even in oceanography, 50 m / 200 km is not steep.
Line 34. The largest slope is at different values of y in OBS compared with SODA and HYCOM, so not “reproduced”.

Page 9 figure 3. The separation of these profiles ~ 1.9 °N is much more than the 100 km “grid” of section 2.2.

Page 10
Line 17. “observed to start at 69° E on day 102, propagate westward with a phase speed of 0.2 m s^-1 and arrive at 60° E on day 155." Presumably this is from SSH from altimetry. This may explain how you can “see” propagation (WPD). But what exactly is propagating?
Line 32 to page 11 line 1. 0.1 m/s is not “relatively weak” compared with typical currents in figure 5.

Page 11.
Line 13. “which agrees with the ASHSW definition”. I don’t think a movement can agree with a definition. Please rewrite the lines 12-14 sentence.
Line 30. “The CTD and XCTD data are precise in reconstructing the three-dimensional oceanic data.” But in section 2.2. you said that “The data are then projected into the standard CR section” which is only 2-D. And indeed the stations in figure 1 have very little x-extent.

Page 12.
Lines 3, 4. “extension” -> “extent”? And many other places?
Line 7. “3D variation” -> “a 3D variational” (twice) ?
Lines 7, 8. “optimum” -> “optimal”?
Line 8. “constraints” (spelling).
Line 9. Omit “on”
Line 12. “mode” -> “structure”
Line 15. “in” -> “to”. “easy” -> “easily”
Lines 17-20. This is very unclear. How can the “present . . results”, down to 1050 m only, be useful in a study of a hydrothermal plume event below 2500 m?

Page 13 line 2. “HYCOM and SODA misinterpret some meso-scale eddies”. I did not see where you state the time-period of the HYCOM and SODA reanalyses. Eddies move! Why should we expect HYCOM and SODA to match the May 2012 observations?

Page 17, figure 4 caption lines 2-3. “. . 20° are highlighted in the potential temperatures . .”

Dear authors.
Thank-you again for your revised manuscript. Both original reviewers have now commented, much more favourably but still with some serious concerns. I am not sure how much you have seen so I include all the comments below (Reviewer 1, Reviewer 2 and Editorial). Please address all of these in a re-revised manuscript.
Yours sincerely
John Huthnance


Reviewer 1
The authors have made substantial changes to the manuscript. I would suggest the authors make minor revisions to make the manuscript easier to read.
1. Figure 2. “monthly wind verctor…”. Monthly-climatological or May 2012?
2. Figure 4. What periods of data are used for SODA, HYCOM, and WOA?
3. Could you highlight the 22kg/m^3 isopycnal in Figure 4?
4. “comparison implies that the year 2002 is an anomaly year for the distributions of ASHSW, PGW and RSW.” Could you give some interpretation here？Maybe you could add a sub-graph to show the wind anomaly in May 2012 in Fig. 2, if the conclusion “the ventilation is induced by surface wind” is correct.
5. Too many abbreviations are not benefit for reading.
6. Figure 6. As you discussed Fig. 6e first, and then Fig. 6c and Fig. 6a, you may want to rearrange the subgraphs.
7. Please add some information about the “starting/ending point” in Figure 6 caption.
8. “We set some passive tracers along the CR.” Do you mean you set the traces along the CTD/XCTD stations shown in Fig. 1? If so, it would be helpful to show the section in Figure 6.
9. To me, the title is not appropriate.
10. The revised “Introduction” is much better than the former. I noticed you raised several questions: pathways of water masses, and mechanics for their moves are not clear. The meso-scale eddies and planetary waves are not sufficiently observed. The internal dynamics of planetary wave is not sufficiently addressed. I also noticed you added several sentences to state the purpose/content of this manuscript: “First, hydrographic survey takes a snapshot on the water mass, and gives an evidence on the activity of water mass. Second,…”. I feel like there is a disconnect between the “existing questions” and the “answers”. I thus kindly ask the authors to think about this issue more, in order to make the manuscript better.


Reviewer 2
I thank the authors for revising the original draft of this paper, and for responding to my first review. This second draft is an improvement on the first – in particular the comparison of the observations and the re-analysis products – although there are a few points that I think require some further work.
I agree with the authors’ point, made in their response, that the hydrographic observations are useful to our understanding of water masses of the Indian Ocean. But the value of these observations, as currently presented, is still not as clear as it could be. I think that this is because the literature the authors have cited is not the most helpful or relevant. I have taken a quick look at the Lutyen et al (1983) paper, and it appears to be too general to be the sole reference for the spreading of RSW (page 2, line 4). Papers specifically on the water masses of the NW Indian Ocean should be cited. I would encourage the authors to read and consider the following:

Beal et al, 2000. Spreading of Red Sea overflow water in the Indian Ocean. JGR, 105, 8549 – 8564
Bower et al, 2000. Character and dynamics of the Red Sea and Persian Gulf outflows. JGR, 105, 6387 – 6414
Durgadoo et al, 2017. Indian Ocean sources of Agulhas leakage. JGR: Oceans, 122, 3481 – 3499
Han & McCreary, 2001. Modelling salinity distributions in the Indian Ocean. JGR, 106, 859 – 877
Prasad et al, 2001. Seasonal spreading of the Persian Gulf Water mass in the Arabian Sea. JGR, 106, 17059 – 17071
Prasad & Ikeda, 2002. A numerical study of the seasonal variability if Arabian Sea High-Salinity Water. JGR, 107, 3197
Prasanna Kumar & Prasad, 1999. Formation and spreading of Arabian Sea High-Salinity water mass. JGR, 104, 1455 – 1464
Shapiro & Meschanov, 1991. Distribution and spreading of Red Sea Water and salt lens formation in the northwest Indian Ocean. 38, 21 – 34

These papers should help to better place the authors’ valuable observations – for instance, the southward extension of ASHSW – into an informative context, both in the introduction and the discussion. As it stands, the main conclusion regarding water masses is that ASHSW is found a little further south in the present observations than in a climatology: I don’t think that this is enough.
The scientific message of the paper would be improved further if the particle tracking were better integrated with the discussion of water masses. The final paragraph of Section 3.4 still feels a little brief. As such, the scientific value of the particle tracking is not clear. Again, I would encourage the authors to discuss the results of their experiments in the context of work specific to the NW Indian Ocean, and the papers listed above should also be helpful here. Trajectories in the PGW and RSW layers are potentially very informative given the distance between the Carlsberg Ridge and the Persian Gulf/Red Sea. Plotting the temperature/salinity properties of particles at the time and location of initiation might also be very informative.
Regarding the interpretation of the particle trajectories, I am not convinced that the westward trajectories visible in Figure 6(e) are the result of eddy transport – surely the trajectories are too straight for this to be the case? Given the location of this westward flow and the SODA velocity distribution presented in Figure 5, is it possible that these trajectories represent transport by the WPPW?
The methods section is much clearer than in the previous draft. Now that I understand what the authors have done, I have a couple of points to raise. Firstly, I am not convinced that no calibration is required. The differences between the CTD and XCTD are, at depth, not insignificant. If the variance about the quoted mean difference in the intermediate ocean is not excessively large, I would have thought that calibration of the XCTDs against the ship’s CTD would be necessary. Secondly, if Argo observations are already processed and calibrated by the Argo programme prior to being made available – and given that the distance between the Argo and CTD profiles is almost twice that between the XCTD and CTD profiles – I would have thought that this comparison could be removed: it doesn’t add anything.
Finally, I remain puzzled by the discussion about ventilation (page 8, final paragraph). Firstly, the definition of the mixed layer given in the authors’ response to my first review should be included in the paper, as it is relevant to the discussion. Secondly, the authors state that north of the outcropped 22.0 kg m^-3 isopycnal, downwelling is likely occurring. But I cannot see how downwelling would produce the upward doming of the near-surface isopycnal at this location. Have the authors considered that this could be a boundary between high-salinity ASHSW in the centre of CCE1 (northern limit of the section – and it’s a cold-core eddy, so we would expect upwelling in the centre?) and fresher surface water outside of the eddy (i.e. to the south)?


Editorial comments as previously sent to improve clarity.

Page 2.
Line 15-16. “The phase speed of west-propagating planetary waves (WPPW) is used to match the theoretical Rossby wave”. This sentence is unclear. I think not “is used”. Does it refer to previous work (give a reference) or to the present manuscript (move it to a better place)?
Lines 19-20. “interdisciplinary survey” (spellings).
Line 21. Not “activity”. Maybe “movement” or “distribution”.
Line 31. “All stations were mainly located”. Either “all” or “mainly” (which means most but not all) – but not both! Perhaps you mean “located close to the CR section”.

Page 4 line 3. Better “. . stations in these comparisons . .”

Page 6
Line 19. Better omit “sufficient” (what is the upwelling sufficient for?).
Line 28. “which refers to the” -> “with respect to its”

Page 7
Near bottom “current is -0.38 m/s. . .” Why “-“? (presumably because westward). A magnitude must be positive.
Your response to reviewer 2 refers to Maximenko et al. (2005). You should cite it here.

Page 8
Line 16. “and show a clear” -> “suggesting a”. Not “clear” because only one isotherm.
Line 27. Better “When we move forward to” -> “In”

Page 10 lines 19-20. Please explain “observation-based absolute geostrophic current”. Maybe you need a subsection 2.n about this. I see you have a sentence in the conclusions – too late!

Page 11 line 28. “The CTD and XCTD data are precise in reconstructing the three-dimensional oceanic data”. This is a bold statement! The second horizontal dimension (x) is hardly measured except at the surface. So there have to be assumptions about the profiles away from the CR section.

Page 12 lines 25-29. The meaning of this sentence is unclear because the grammar is wrong. Please break it up, decide what is the most important part, give every clause a verb.

Dear Authors
Thank-you for your re-revised manuscript. There are still some comments to address. Please see below.
Regards
John Huthnance (editor)

Regarding Referee 1: title. Please think again. Yes, your title is specific enough, but what readers want to know is not that you did a hydrographic survey but what you learned from it. The title should reflect the new science, e.g. “Anomalous distribution and movement of distinctive water masses in the north-west Indian Ocean, May 2012”. But don’t just copy this, choose your own title.

Regarding referee 2: what is the benefit from the particle tracking with SODA and HYCOM since you say that their currents are wrong? You need to discuss – probably in section 4 – how similar or different are the water masses suggested by the particle tracking compared with the hydrography. Are the differences consistent with the error in the reanalysis currents (and hence particle tracks)?

Here are some more detailed comments.
Page 2
Lines 4, 17. Better “mechanics” -> “dynamics”
Lines 13-15. These seem to be in random order. Go clockwise from one coast to the other?
Line 27. “(WPPW) is used to match the” -> “(WPPW) has been matched to the”? Anyway, if you are describing previous work then not “is” but “has been”.

Page 3
Lines 1-2. “clear objective” (what is it?) and “analyze” (for what?). This is the place to say explicitly what are the objectives! You could repeat the three “reasons” in the previous three sentences. Or better re-write all four sentences so that you emphasise the science to be gained and not the methods. Methods are described in section 2.
Line 19. “instrument” –> “different instruments”

Page 7 lines 7-12. In a previous response you said “As refer to Maximenko et al. (2005), present observation displays the vertical structure of this westward current. The related theory needs to be further confirmed. Maximenko, N. A., Bang, B., and Sasaki, H.: Observational evidence of alternating zonal jets in the world ocean, Geophysical Research Letters, 32, L12607, 2005.” I then said that you should include this and reference to Maximenko et al. (2005) in your manuscript. You have not! However, I am not sure what is the point of your previous response. If your previous response is saying that now you show the vertical structure of the westward current, and this is new (and certainly an improvement on Maximenko et al. 2005), then you should say this in your manuscript. However, that may be most relevant at page 10, line 27.

Page 8, figure 2 caption, end. “consistent surface geostrophic current”; do you mean “corresponding surface geostrophic current” meaning that it is consistent with the surface height?

Page 10
Line 1. “2002” -> “2012”?
Line 10. “crops out” -> “outcrops” or “surfaces”.
Lines 17-18. Regarding referee 2: “Finally, I remain puzzled by the discussion about ventilation . . the authors state that north of the outcropped 22.0 kg m^−3 isopycnal, downwelling is likely occurring. But I cannot see how downwelling would produce the upward doming of the near-surface isopycnal at this location. Have the authors considered that this could be a boundary between high-salinity ASHSW in the centre of CCE1 (northern limit of the section – and it’s a cold-core eddy, so we would expect upwelling in the centre?) and fresher surface water outside of the eddy (i.e. to the south)?”
Your response: “. . . Regarding the isopycnal layer, we simply matched the density structure as the multi-layer model, where the 22 – 22.5 kg m^−3 layer exposed to the surface, and took part in the air-sea interaction (Figure 4; density structure).”
I do not understand the relation of your response to the question. And I am puzzled by your present text “The upper ocean density fields from SODA and HYCOM also show clear ventilation structures. From the observations, equatorial waters with a potential density of 22 kg/m^3 at a depth of 30 m are rising to the surface.” Where are the “ventilation structures” and why “ventilation”?
Line 27. Not “well rebuilt”. Maybe “clear” or perhaps “well represented” but if you say “well” you need to state the basis on which you claim good quality.
Line 34. Surely “. . upper 200 m, where the current speed . .”?

Page 11
Line 2. “and merges with the WPPW. . .”
Lines 22-23. “The results support ASHSWs are mainly from the Arabian Basin . .” This is not meaningful – where else would ASHSW come from? I think you want “The results show water coming mainly from the Arabian Basin . .”
Line 23. “into” CR. In” -> “onto the CR. On”
Line 25. “start at the east” -> “starting east”
Line 26. Delete “at the”
Line 33. “. . Meanwhile, pathway directly from northwest is emerged, and the trajectories support 700 m waters are”. I think you mean “. . Meanwhile, there are pathways directly from the northwest and other trajectories show 700 m waters coming”

Page 12
Line 2. Better “. . westward trajectories resemble the prediction of ventilation theory . .”. However, if you say this you need to say more about what currents are expected from ventilation theory and why.
Line 11. “thus” -> “because they”
Line 31. “Indian” ->”India”
Line 33. Delete “the”

Page 13
Line 11. “display clear ventilation structures”. You can only say this if you answer the points above regarding page 10 lines 17-18 and page 12 line 2.

Dear Authors
Thank-you for your revised manuscript. I am asking for “Technical corrections” according to the detailed comments below. Then your manuscript should be entered in the OS editorial system with no more intervention by myself. However, there will be copy editing and you should check that the final version keeps your intended meaning.
Thank-you for publishing in Ocean Science.
Yours sincerely
John Huthnance

Detailed comments
Page 1
Line 7. Omit first “the” or say what climatology you refer to.
Line 14. “Somalia” -> “Somali”

Page 2
Line 15. “First” -> “the first”
Line 18. Omit first “the”
Line 22. “. . hand, meso-scale . .” (omit “the”).

Page 3.
Line 2. Better “. . evaluate widely-used oceanic reanalyses.”? “. . trajectories of Argo floats . .”
Line 4. “. . eddies and a planetary wave, . .”?
Line 5. “reanalyses . .”
Line 13. “we limited our analysis to depth 2000 m”. Perhaps 1050 m as in figures and page 13 lines 11, 13?
Line 15. “simultaneous” -> “contemporary”

Page 4. Figure 1 caption, line 1. “simultaneous” -> “contemporary”

Page 10, line 27. “side” -> “end”

Page 11.
Line 15. “in” -> “at”
Line 16. “in” -> “over” (twice).
Line 33. Insert “band” after “9.8°N”
Line 34. “coincident” -> “accords”

Page 12
Line 2. “. . support the idea that 700 m waters . .”
Line 11. “. . interior fields can be derived . . density), but a reliable . .”

Page 13
Line 1. “. . reanalyses differ: the southward extents of ASHSW are not the same . .”
Line 5. “mechanics” -> “mechanism”

Page 14
Line 4. “and” -> “or”.