Review of revision of "Moored observations of mesoscale features in the Cape Basin: Characteristics and local impacts on water mass distributions"
General comments:
The authors should be commended for undertaking a major revision of this manuscript, addressing several of the points raised during my review of the original manuscript. However, many aspects of this paper remain problematic.
First, the main issue concerns the definition of eddies as captured by the still unpublished Laxenaire 2018 manuscript. Despite using the method of Lilly and Rhines, as suggested, I am still not convinced that the features identified by A13 and A16, as an example, really constitute coherent "eddies". I think it might be a too difficult approach to be willing to define such features in the "Cape Cauldron" region. Since the Laxenaire 2018 manuscript is not published yet, we do not know its performance. This is demonstrated by Figure 3 which is really incomprehensible. I think the authors would be better off talking in general about mesoscale features affecting the mooring measurements. In a revised, or different, version of this manuscript, the authors should start with analyzing more scrupulously the time series of temperature, salinity, and current rather than taking the approach of analyzing altimetry first. If the authors would like to pursue the coherent eddy approach, I suggest they use the Chelton database as a starting point.
Second, I have concerns about the processing and calibration of the microcat data. In my detailed comments below I have many questions about the description of the processing of the data. Most of the statistics and numbers given do not make much sense at all. The following sentence exemplifies the problem: "When regressed with the CTD temperature and salinity, all the SBE MicroCat's sensors had a root mean square (rms) values greater than 0.9999 for both temperature and salinity." What does this even mean?
Figure 11 may also illustrates the issue as well. Why are the data from the microcats so distinct from the data from the CPIES (for the lightest density classes)?
Finally, the whole topic of nonlinearity is dubious. The Rossby numbers provided (~0.1) suggest that linear geostrophic dynamics are taking place. What is left is the characterization of eddies as "nonlinear" as defined by Chelton where the translation speed is less than the tangential speed and water parcels are expected to be trapped within the eddies. I would have liked to see more clearly in the manuscript the connection with water mass intrusions in the mooring data.
Finally, I have many many detailed comments, listed below.
In conclusion, I cannot recommend the publication of this manuscript in its present form.
Detailed comments:
l14-15: can delete "the latitude"
l16: official name is "Current and Pressure Recording Inverted Echo Sounder"
l24-25: "Under three case studies, the full-water column hydrographic properties of each mesoscale feature has been evaluated.": I am not sure what this sentence means. Do you imply that with only 3 case studies you evaluated the properties of ALL the mesoscale features that passed your array? Is this demonstrated in the paper? I believe this sentence could be deleted from the abstract.
l34: what is "large-water mass distribution"? Do you mean large-scale water mass distribution?
l39: lives -> leaves
l44: implications are for "climate" or "climate processes", not "studies"
l52: its? do you mean theirs?
l54: "on pre-AVISO" -> "before". AVISO is not the same as altimetry.
l60: "distinguished" is not the right word: "characterized", "identified" maybe?
l62: "mixing": what type of mixing? vertical? horizontal?
l67: "described"? Do you mean "found"? "identified"?
l72: " theoretically described by numerical models": what does this mean?
l46 to l83: Could you break down this very long paragraph into several paragraphs? The last part is an extensive literature review, which is welcomed, but is not well organized.
l101: how is it "ideal"?
l111: Current and Pressure Recording Inverted Echo Sounder
Figure 1 caption, l740: Figure 1 Etopo1 - > ETOPO1 I believe
Table 1: What is "ensemble lengths"?
l121: "Some of these instruments also have pressure recorders ... but these sensors will not be used in this study": you did not use the pressure data to calculate salinity from conductivity? Did you use a nominal pressure/depth for the calculation? Was there any blowdown of your moorings?
l131: Why did you calculate daily averages when you already applied a low pass filter with a 3-day cut off? Calculating daily averages amounts to low pass filtering so it is redundant.
l133: What is the region from which you used hydrographic data to build the GEM? That is important information what should be indicated.
l139: Beal et al. 2015 and Elipot and Beal 2015 also applied successfully the GEM method with CPIES in the nearby Agulhas Current.
l139: \tau: have you defined it earlier as travel time?
l140: Tab?
l148-150 : "This calculation leads to the estimate of the advection direction \Theta as the largest velocity is expected in the direction perpendicular to the mean advection flow (direction of V_n).": this sentence is odd, could you rephrase?
l166: Please update the van den berg 2015 reference by indicating where the report cab be found. I was actually able to find online the report for the RS Algoa voyage 221: I could not find anything in this report on the CTD calibration and quality control. This raises questions on the quality of the data and the validity of the microcat calibrations against the CTD data.
l167-173: The whole method of calibrating microcats originates from Kanzow et al. 2006 (doi:10.1016/j.dsr.2005.12.007). Please refer to the methodology in this publication and to the accuracy requirements for the instruments.
l167: "were within an envelope of 0.005 wide"? I do not understand this, please explain better. What are the units?
l168-173:
"Once calibrated?" What? the CTD? The final processing of all data is surely done after the cruise; please revise.
"were attached to the CTD": you mean the rosette? the package?
"When regressed with the CTD temperature and salinity, all the SBE MicroCat's sensors had a root mean square (rms) values greater than 0.9999 for both temperature and salinity.": This does not make any sense. Are you talking about regression coefficients? RMS value of 0.999 in which units?
"The average standard error for the temperature (salinity) regressions were equal to 0.012 (0.002).": Not sure what you mean here. Are you talking about residuals?
The SBE 37-SM Microcat has an initial temperature accuracy of 0.002 C (see manual of instrument). If your standard error for temperature is 0.012 C based on your regression/calibration with the CTD, isn't this worth commenting on?
Here you give numerical values for salinity. Can you give first numerical values for conductivity?
Figure 2: It would be better for legibility to set the contour colors to "none" (if using Matlab as an example) and use discrete (instead of continuous) color scales. Water depth is usually positive, as in your Table 1.
l174: "In addition": to what?
l181: extremum -> extrema?
l182: Only 1mm? Are you sure this is the right value? Eddies should be associated with SLA on the order of 10 cm or so.
l194-195: do you mean Figure 4?
l228: "the median radius and standard deviation of these features are equal to 85 ± 43 km (66 ± 38 km considering the solid body rotation)": the two type of analyses (solid rotation or not?) are not necessarily obvious. This requires more explanation. Please expand.
l232: It looks like Figure 4 might have been introduced before Figure 3?
Tab III caption: generate -> generated?
l242: Sometimes you spell "Figure", sometimes you use "Fig"
Figure 3 is not very insightful: Take as an example the blue lines connecting C8, C9, and C25: are we supposed to be able to distinguish where these eddies went?
Figure 5 caption:
l764: "are identified as close enough to affect the measurement at the different moorings.": I think you mean something like: "are shown to affect the measurements ..." (even if I am not always convinced)
Figure 6 caption:
l771: dote -> dots?
l772: same ... than -> same ... as
l257: A12 is really dubious in Figure 5i: Figure 5 does not show all contours of ADT so it is rather difficult to assess what the Laxenaire 2018 algorithm does. However, it can be seen that the western side of this anticyclone has no velocity signature, nor a SST signature. It looks like the east side is a branch of the Benguela current. I am finding this sequence of eddies hardly convincing. How can you explain the size of A13? It goes back to my comments about the original version of this manuscript.
l266: which intense dipole? April 18?
Figure 4: As it stands, I am not convinced that the time series of u and v really allow the reader to see the influence of the alleged eddies. Maybe the Figure could show stick vector diagrams instead of u and v time series curve?
l289-290: "A filament or a front is also characterized by a straight line as for an eddy sliced through its exact center.": as? What do you mean? Do you mean that a filament or an eddy sliced throught its center lead to the same type of hodograph?
l293: "impulsive-like"? impulsive does not describe a visual feature but an emotional state. Do you mean a pulse maybe? Please explain better.
l294: "theoretical"? That has more to do with kinematics
l296 and l299: "associated to" -> associated with
l297: "first SBE Microcat's": please indicate the depth
l300-302: check the subjects and tense of your verb in this sentence.
Figure 6: This is confusing: you have 3 case studies but 6 events?
l309: It may be a matter of definition but should you not drop the term "eddy" in the case of A13? It looks more like a circulation. A13 is 600km long at least in the meridional direction ...
l316: is it at 450 m (text) or 500 m (Figure 7 caption)?
Figure 8 and others: The issue with displaying the velocity vectors in these figures is that the velocities at the SAMBA line are so much weaker than in the retroflection region. As a result, it does not help your case when arguing that eddies are present at the line. Could you find another way to display these arrows? Use two different scaling? or just show the direction of the velocity? Or show the velocities only near the SAMBA line so that you can adjust the scaling?
Figure 9: A16 is an eddy? This is not credible.
Figure 10: something strange is happening in the top left corner of panel a: please indicate what the contours are and the displayed gray numbers. It looks like something is wrong with the labeling of your contours. The caption needs to be improved. "temperature and salinity ... from the SBE37 MicroCATs colored dots with their associated depth" : what does this mean? Temperature from dots? Finally, I do not understand the difference between panel a on one hand and panels b and c on the other hand.
Finally, I am not sure about the systematic use of "#" for #Anticyclonic and #Cyclonic. What is the point?
l371-372: "While the signature of these two features is clearly separated": in panel b I do not see the blue dots and red dots being clearly separated for the densest classes of water. Can you explain better?
l378: associated to -> associated with
l410: said -> written?
l411: "correlated compared" -> correlated with?
section 3.4: Could you conclude something about the analysis summarized in Figure 11: what have we learned? Is this section about comparing CPIES data and microcat data? Or is it about learning something about water intrusions? Looking at Figure 11, none of the anomalies from the CPIES seem to match the anomalies from the microcats. What does this mean?
l477 to 480: The two following statements are a little bit contradictory, can you try to reconcile? In the intro you talk a lot about nonlinear, then if your Rossby number estimates are small, the conditions are not that "nonlinear"? Or maybe you refer to the definition of nonlinear eddies by Chelton etc.? Can you please add a reference and discuss more.
"The estimation of small Rossby number associated to these features reveals that the momentum equation is dominated by the geostrophic balance between the pressure gradient and the Coriolis forces."
"From altimetry data, these eddies have an azimuthal velocity exceeding their translation speed, confirming their non-linear nature and so their ability to advect a parcel of trapped fluid as they translate." |
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