Vertical Migration of the Along-Slope Counter-Flow and Its Relation with the Kuroshio Intrusion off Northeastern Taiwan
, Po Hu 1,3,4, Yuqi Yin 1,3,4, Ze Liu 1,3,4, Yahao Liu 1,3,4, Yijun Hou 1,2,3,4,* and Yuanzhi Zhang 5Round 1
Reviewer 1 Report
In this manuscript, the authors observed the surface cyclonic eddies uplifted the counter-flow in the subsurface layer and surface anticyclonic eddies lowered the counter-flow in the subsurface layer from ADCP data. They also found that the vertical migration of the counter-flow was closely linked with the Kuroshio intrusion (KI) to the northeast of Taiwan. The authors tried to figure out the causes of the uplifted and lowered of the counter-flow in the subsurface layer. However, after reading the manuscript, this reviewer still has no way of knowing the mechanisms. The environment of the study area is so complicated. Besides the Kuroshio intrusion, the authors may take into account different mechanisms at different locations, such as eddy, cold dome shift, wind, and so on. Therefore, this reviewer cannot recommend this manuscript be published in Remote Sensing. The following suggestions are given for improving the quality and scientific issues of this manuscript.
Major comments:
1. The counter-flow off northeast Taiwan shown in Figure 1 is a southwest current flows to the northeast coast of Taiwan. The authors claim that the counter-flow rose during the summer months (May – October) and fell during the winter months (November – April). However, in Figures 2a and c, most currents flow shoreward, that means northwestward, but in Figures 2b and d, most currents flow northwestward during the summer months. This is in contradiction with the statement of counter-flow and the flow direction shown in Figure 1.
2. Although the positions of D1, D2, and D3 are located along the 200 m isobath, mechanisms of the counter-flow at each position may be different. The mechanisms cannot be simply estimated and ensured by parameters such as KI and SKI.
3. Lines 258-259, how and why did the author ensure that the counter-flow in the subsurface layer is uplifted and lowered depending on the surface eddy variations?
4. Figures 8 and 9, is the black line in each subplot the best fit regression line? It looks not the best fit line.
Minor comments:
1. In caption of Figure 1, please give the detail position (longitude, latitude) of D1, D2, D3, and ADCP.
2. Lines 68-70, “a better understanding of the KI off northeastern Taiwan help oceanographers to make a better prediction of the fisheries in the seas off northeastern Taiwan, eastern Zhejiang, and in the East China Sea”, please describe more detail how to predict the fisheries between the KI and these three area.
3. Section 2.1.2, it is necessary to list the dataset or doi number of ADCP data where the data can be downloaded.
4. Section 2.1.3, it is necessary to show what the dataset name and version that the authors used from CMEMS website.
5. Section 2.1.4, it is necessary to show what the version that the authors downloaded from HYCOM website.
6. Lines 144-150, add more detail about how to calculate the axis depth, and what is the meaningful of axis depth? Why did the authors use only southwestward counter-flow?
7. Line 155, how to decide the angle of geostrophic velocity direction? Is it the same as that in line 174?
8. Lines 204-205, where is the upper boundary and axis of the counter-flow?
9. Lines 227-229, please add more detail about the correlation with the near 10-d periodicity and Kuroshio baroclinic instability waves.
10. Lines 229-230, why the near 15-d periodicity could be attributed to the lunisolar synodic fortnightly component of the tidal signal?
11. Lines 233-236, more discussions about the relationship between positive/negative GVA curl and the counter-flow are needed. In addition, it is necessary to explain why the counter-flow could also be uplifted during winter months.
12. Line 244, it should be "...an uplifted case and a lowered case are presented in Figure 5 and Figure 6, respectively."
13. Figures 5 and 6, subplots are too small to be read. Please enlarge them.
14. Lines 265 and 277, why show the 26.5°C and 28°C isotherm in Figure 5 and 27.5°C and 29°C isotherm in Figure 6?
Author Response
Dear Reviewer 1:
Thanks for your critical comments.
We have revised and improved the manuscript based on your suggestions and comments as attached.
Submitted is the revised version and reply to all comments.
Yours sincerely,
Yuanzhi Zhang
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review of Vertical migration of the along-slope counter-flow and its relation with the Kuroshio intrusion off northeastern Taiwan" by Yuanshou He, Po Hu, Yuqi Yin, Ze Liu, Yahao Liu, Yijun Hou, Yuanzhi Zhang.
In this study, the authors investigate variations of southwestward counter-current along the continental shelf off northeast of Taiwan, and its relation to the Kuroshio intrusion onto the shelf of the East China Sea. Several indices are calculated on the basis of in-situ observation, satellite altimeter, and assimilation model results to characterize the position of the Kuroshio, vertical structure of the counter-current, intrusion of the Kuroshio water, and so on. The topic of this study is interesting and to understand the mechanism of the intrusion of the Kuroshio water onto the continental shelf northeast of Taiwan is important from the point of view of not only physical oceanography but also biogeochemistry. However, there are some points to be improved or to be clarified as shown below.
Section 2.2:
Various indices are introduced, but purpose of using such indices is not clear. Besides, many of them such as KAA (Kuroshio Axis angle), KAP (Kuroshio Axis Position), and KCI are not linked to conclusions of this study. I think it would be better to remove such indices.
L151:
The term "volume transport" is misleading. KVT (Kuroshio Volume Transport) defined in L154 means just a zonal integration of surface velocity, and is therefore completely different from Kuroshio transport.
L163:
What is v(s) ? Does it denote cross-isobath component of horizontal velocity ? It should be clarified.
L219 (caption of Fig.2):
"southwestward (northeastward)" should be "northeastward (southwestward)" ?
L231-232:
What kind of factors do you suppose for variation of the counter flow with a period of about 20 days ?
Figure 4:
It would be better to remove seasonal variation from SLA and redefine SLA as a deviation from mean sea level for the analysis period.
L243:
"vertical velocity" is incorrect. What is shown in Figure 5d is not vertical velocity but "vertical distribution of velocity normal to the section NL.
L244:
"Figure 5a,b and Figure 5c,d" should be "Figure 5 and Figure 6".
L246-252:
How are the surface eddies generated ? It seems to be related to Kuroshio path variations as a result of interaction between westward-propagating mesoscale eddy and the Kuroshio east of Taiwan.
L317-325:
Relation between mesoscale eddies and intraseasonal variations of Kuroshio intrusion across the continental slope northeast of Taiwan should be discussed on the basis of analysis results in this study.
L339-366:
Relation between Kuroshio intrusion and variations of the counter-flow is the main target of this study. However, this relation is investigated only by simple correlation analysis. As a result, physical mechanism is still unclear. The authors should investigate the relation between Kuroshio intrusion and variations of the counter-flow more carefully.
Author Response
Dear Reviewer 2:
Thanks for your critical comments.
We have revised and improved the manuscript based on your suggestions and comments as attached.
Submitted is the revised version and reply to all comments.
Yours sincerely,
Yuanzhi Zhang
Author Response File: Author Response.pdf
Reviewer 3 Report
Reviewer comments
Line number:
36: “intrudes” instead of “intrude
37: “indicate” instead of “indicates”
43: “is directed towards southwest” instead of “travels southwestward”
46: “flow” instead of “movement of water”
75: “located” instead of “locates”
78: “are found” instead of “are easily to be found”
80: “resulting” instead of “thus result”
81: “Kuroshio waters” instead of “Kuroshio water”
83: “it is usually considered” instead of “usually considered”
99: “carried out” instead of “obtained”
102 “bin” instead of “pin
103: “was again deployed” instead of “was deployed”
104: “2018;” instead of “2018,”
137: “vertical temperature” instead of “vertical temperatures”
148: Formula to calculate Da, the counter flow axis depth. Wouldn’t be more direct to search for the depth of max (vsw) flow instead of Da as proposed? A weaker vsw at a greater depth will have the same weight as a stronger one at smaller depth!
154: Formula to calculate KVT. Instead of vg, its component normal to the section shouldn’t be used?
155: Formula to calculate KAA. It is not clear what value of vg is used: is the magnitude of the vector vg? Is theta angle defined in the trigonometric sense, so that theta=0 corresponds to the flow is towards east, and theta=90 towards north? Wouldn’t be more direct to check where is the core of the jet (maximum of current) and take the direction of the flow there as theta?
163: A more detailed explanation on how KI is being calculated is deserved. What is v(s)? Is it the magnitude of the current? Explain it better what is ds. Are you talking about vertical grid cells from bottom to the surface along the 200 m isobath? An intrusion of Kuroshio wouldn’t be associated only with a flow across the isobath?
164: Explain it better formula for SKI. Text says “? indicates line direction manual given in the altimeter data”. Please, clarify this point.
181-186: Here it is somewhat confusing: now theta angle is between flow direction near topography and direction of topographic gradient as it should be (therefore, it is not the theta as calculated by KAA formula). It is said that this angle “is unknown within the ocean interior due to the lack of flow field data”. But this lack of field data couldn’t it be solved by using the model results? Please, clarify it better how the ratio between KVT and KAA can be used as a proxy of upwelling tendency.
186: Without a better explanation it is not clear why KCI, as defined, is a proxy of Kuroshio upwelling index.
187-188: Phrase “To make quantitative estimation … counter-flow.” seems linked to next one; please fix it.
216-219: Legend of Fig. 2 seems incorrect. Isn’t blue color indicating the counter-flow, i.e. the southwestward velocity, instead of northeastward, as stated?
243-244: This text doesn’t match with figures Fig. 5a,b,c,d. It seems the correct would be: “The horizontal GV field, SST field, GVA field and the vertical velocity field during an uplifted case and a lowered case are presented in Figure 5a,b,c,d and Figure 6a,b,c,d, respectively.” Please, verify it.
247: “vertical distribution of horizontal velocity” instead of “vertical velocity distribution”
285: It seems that it should be “Kuroshio Current transports” instead of “Kuroshio Current transporting”
289: “indicate” instead of “indicates”
301: “indicate” instead of “indicates”
303: Explain or rephrase “island-fortify patterns”
343: Explain what is meant by “standardized KAP, KAA, KCI …”.
339-340: “To make quantitative … counter-flow.” Phrase is without sense.
360: “were” instead of “ware”
381: either “for using” or “to use” instead of “for use”
383: “is directed towards southwest” instead of “flows southwestward”
385: “has found” instead of “found
403-404: “The 10-d signal could be to Kuroshio baroclinic instability waves”: this is not a conclusion of this paper since there was not analysis to justify it. It only reproduces a conclusion of other paper and should be so stated.
Author Response
Dear Reviewer 3:
Thanks for your critical comments.
We have revised and improved the manuscript based on your suggestions and comments as attached.
Submitted is the revised version and reply to all comments.
Yours sincerely,
Yuanzhi Zhang
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
See attached file
Comments for author File: Comments.pdf
Author Response
Dear Reviewer 1:
Thank you very much for your comments and suggestions.
We have revised and improved the manuscript according to your suggestions.
The data will be separately uploaded by the first author, while I only submit the revised version and reply to all comments.
Yours sincerely,
Yuanzhi Zhang
Author Response File: Author Response.pdf
Reviewer 2 Report
The revised manuscript has been improved, and it is now acceptable for publication.
Author Response
Thank you very much.
Reviewer 3 Report
No further comments for authors.
Author Response
Thank you very much.
