Characteristics and Drivers of Marine Heatwaves in 2021 Summer in East Korea Bay, Japan/East Sea

Round 1

Reviewer 1 Report (New Reviewer)

Review of the paper “Characteristics and Drivers of Marine Heatwaves in 2021 summer in East Korea Bay, Japan/East Sea” by Chen et al.

 General Comments:

 Based on satellite remote sensing and reanalysis products, the authors studied the characteristics of MHWs in the JES over the past four decades, further focusing on the spatiotemporal characteristics and mechanisms of MHWs in the EKB area from June to August 2021. They concluded that these summer MHWs are caused by a combination of three reasons, including the atmospheric high-pressure system, the net positive lateral heat fluxes, and the weak sea surface wind.

The paper covers an interesting topic and fits the scope of the journal. It would be a good contribution to understanding the characteristics and physical drivers of regional MHWs, which is also significant for discussing their potential ecological impacts. The language is generally easy to follow. The manuscript is also well structured. But it also suffers from some major issues. I would suggest a major revision before the potential publication of the manuscript.

Major comments:

(1)    The major concern is the explanation of the contribution of lateral heat fluxes from open boundaries to the occurrence of the marine heatwave in Section 3.3.2. A negative total heat flux means a heat loss from the EKB domain, which means that there is heat accumulation in the EKB area only during August 06-13. For the other periods, it is heat loss. Therefore, it is not reasonable to say “obvious heat increase during Jun 18-27 (AB) and July 20-Aust 11 (CD)”, it should be “less heat loss during Jun 18-27 (AB) and July 20-Aust 11 (CD)”. It also does not fit the fact by saying “lateral heat flux, mainly in late July and early August, maintains a high SST”.

Based on those facts, it cannot conclude that the net positive lateral heat fluxes are one of the major factors contributing to the occurrence of the specific MHW.

(2)    Furthermore, Kuroda and Setou (2021) investigated the extensive marine heatwaves in the Northwestern Pacific Ocean in the summer of 2021. Their study covers an adjacent region and concluded that “the MHWs were generated mainly by atmospheric forcing associated with northwestward expansion of the North Pacific Subtropical High and northward displacement of the westerly jet”. It would be worthful to discuss the reasons for the different mechanisms between the present study and Kuroda and Setou (2021).

(3)    Several figures’ captions are not well explained. To name a few: Figure 1: The location of the study area is marked (L98-L99: “127.3°E-132.5°E, 38°N-42°N”) inconsistently with the data described in Section 2 (L113-L114: “127.3°E-132.7°E, 38°N-42°N”). Figures 2 and 3: It is not clear to me which period SST data you used to analyze the MHWs, all summers or all years? The “multi-year average” in L173 refers to the “multi-year summer average”, right? Please indicate clearly in the figure captions.

(4)    The format of partial subheadings and figure captions is not standardized. Such as L105: “2.2.1” should be “2.2.1.”, L394: “4.2” should be “4.2.”, and L315: “Figure 6” should be “Figure 6.”. Please check the manuscript carefully.

Minor comments:

L49: It is not clear to me whether it is increased by 17 times or 17%, please indicate clearly

L64: “indicate” would be “indicated”.

L88-L90: delete the sentence.

L116-L117: “Archiving Validation and Interpretation of Satellite Oceanographic (abbreviation as AVISO)” would be “Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO)”, please also indicate the period of used data and list the reference.

L123-L125: “fifth‐generation global atmospheric reanalysis data from the European Centre for Medium‐Range Weather Forecasts (abbreviation as ERA5)” would be “fifth‐generation global atmospheric reanalysis data (ERA5) from the European Centre for Medium‐Range Weather Forecasts (ECMWF)”.

L126-L128: why not use Monthly geopotential height data at 500 hPa from ERA5 as those data from L122-L123?

L145: The formula format of MeanInt has an extra parenthesis in Table 1.

L163: D is mixed layer depth?

L197: change “occur long-term extreme events” to “persist for a long-term?”

L218-L221: Please put a space between the unit and the number, such as L218: “2.8°C/count (2.2°C/count)”, L220-L221: “50°C”, “140°C”, “80°C”.

L248-L251: Modifications as above, “5-6.5°C”, “4.5°C”, “3.8°C”, “150-170°C”, and “120°C”.

L423: “4.5°C” would be “4.5 °C”.

L423-L431: Conclusions are the same as Abstract in L30-L35, please use different sentences to describe.

L524 The reference format is not standardized as the others

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report (Previous Reviewer 3)

I have read the authors' responses to my comments and am satisfied that this paper is now suitable for publication.

Author Response

Thank the reviewer for the time spent on our manuscripts. The comments and suggestions by the reviewer before were of great help for us to improve our manuscripts significantly. Thank you for recognizing us.

Reviewer 3 Report (New Reviewer)

Comments on “ Characteristics and Drivers of Marine Heatwaves in 2021 summer in East Korea Bay, Japan/East Sea” by Chen et al. 

Using satellite and reanalysis datasets, the present study investigated the MHW in the Japan/East Sea. The authors analyzed six indices characterizing the MHW during 1982 to 2021, and found that the most severe MHW events occur in the East Korean in the summer of 2021. The study then focused on the features and mechanism of the MHW in the EKB and its adjacent areas from June to August , 2021. It is suggested that the high-pressure system moving to the EKB, the net positive lateral heat flux, and weak surface wind over the EKB are responsible for the summer MHW in 2021. These results are interesting. My major comments are in the following.

1.      Based on Figure 2, the authors said “It is demonstrated that there are MHWs taking place in the JES in the last 40 years and more and stronger MHWs are found in the EKB area.”. However, Fig.2b shows low-value in the EKB area, which is not consistent with the texts. These texts should be modified.

2.      Line 205: what does “area-weighted” mean? Pls explain why use area-weighted and how area-weighted is calculated.

3.      Lines 205-221: To illustrate the changes in 2008, 2017, 2019, 2020, and 2021, a table may be better than in texts. Moreover, the readers may wonder why Days and Frequency of the MHW in 2021 is the highest. Some discussions may be needed. 

4.      Section 3.3: I am wondering why the authors did not conduct heat budget analysis of the ocean mixed-layer temperature. 

5.      Section 3.3.1: The authors showed the shortwave radiation in June-August 2021. How about longwave radiation, latent heat flux and sensible heat flux at the sea surface?

6.      Lines 363-368: The authors suggested that the summer 2021 MHW is caused by three reasons. How about the relative contributions of three reasons?  

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report (New Reviewer)

A review of “Characteristics and Drivers of Marine Heatwaves in 2021 summer in East Korea Bay, Japan/East Sea” by Chen et. al.

Plagiarism alert

 

Please note that this manuscript is nearly identical to a recent publication in the same journal (MDPI’s Remote Sensing) in terms of methodology, data visualizations, and similar conclusions, except using a different set of data and range of time of interest. 

 

(source) Wang, D.; Xu, T.; Fang, G.; Jiang, S.; Wang, G.; Wei, Z.; Wang, Y.

Characteristics of Marine Heatwaves in the Japan/East Sea. Remote Sens. 2022, 14, 936. https://doi.org/10.3390/rs14040936

 

The authors must justify the scientific contribution of this manuscript. For any contents or methods that are copied from other publications, the authors must sufficiently cite and reference the source from which the current manuscript is inspired. Below shows some examples of why there are concerns about plagiarism.

 

• Section 2 (starting Line 130): most methods used in this paper are identical to Want et al. (2022) without being properly cited.

• Table 1 (starting line 145): Identical table to Wang et al. (2022) with changes in summation or integral signs and slightly different expressions.

• Figure 2 (Line 199): No significant difference compared to Figure 4 in Wang et al. (2022)

Figure 2 in this manuscript and Figure 4 in Wang et al. (mentioned above, source) are basically identical plots with shifted color bars and contour levels. In this group of plots, the only difference is using a different dataset, but the message conveyed from this plot is the same (adding data points from one year out of a 40-year window is NOT statistically significant). 

• Figure 3: Identical visualizations

Almost the same plot in Wang et al. (2022) with a slightly different correlation coefficient and one more data point in each subplot. Similar figures are seen in Figures 13 and 14 in Wang et al. (2022).

• Figure 4 (starting line 252): This figure is just a summary of the lengthy figures 7 & 8 from Wang et al. (2022) with an expanded set of variables, and this figure is only mentioned once by the descriptions between 237 to 250 without future discussions. Suggest adding a reason for plotting these figures and a summary of how the findings strengthened the conclusion.

 

(Below comments are not associated with the concerns of plagiarism.)

 

Line 347: The argument and discussion in this paragraph are very weak. Only numerical values are listed with brief qualitative discussions, but the impacts and the meanings of those values are not properly referenced. Abruptly, a very strong conclusion is appended claiming the reasons that introduced the 2021’s MHW. Also, if you are talking about vertical mixing, it’s better to define the Ekman velocity like Eq. 3 in Wang et al. (2022), but then the paper would look even more identical to that one. How about using stress?

 

Line 386 (figure 10): This figure is very difficult to read, in particular those vectors representing the sea-surface velocity. I assume the surface velocity is derived from the sea-surface anomaly using geostrophic approximations. Since the velocity anomaly and its direction are brought up here (clockwise direction, up to 0.5 m/s), Figure 10 can be replaced with the geostrophic vorticity (g/f ∇∇ z), where z is the sea-level anomalies. Then it would be more obvious to visualize the claimed phenomena.

 

Line 395: Cool idea, and suggest plotting the normalized difference or difference as a comparison. 

 

Line 433: the manuscript discussed nothing about the Ekman currents but oddly mention this as a potential cause of the 2021 MHW events. Suggest either adding discussions or removing the statement.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.doc

Round 2

Reviewer 1 Report (New Reviewer)

Thanks. The authors have addressed all my concerns.  I only have one minor comment: please explain clearly R(P), R(E) and phi in the equation 1

Reviewer 4 Report (New Reviewer)

Despite efforts to revise the manuscript with added citations, the scientific novelty and contributions are very faint in this paper for a remote-sensing journal given the largely similar methodology, data-processing tools, and area of interest. The author may consider a different venue for publishing their study. Thus, I cannot agree that the manuscript is ready for publication. It’s up to the editor to make the final decision.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The article, Characteristics and Drivers of Marine Heatwaves in 2021 summer in East Korea Bay, Japan/East Sea, investigates the change of Marine Heatwaves using satellite and reanalysis data. The main conclusions are 1) the MHWs in this area has a rapidly increasing trend during 2982-2021. 2) there is an extreme MHW in the EKB in the summer of 2021, and the atmospheric factors, rather than oceanic processes, are the main drivers. Overall, this paper contributes to our understanding of MHW in East Korea Bay and Japan/East Sea. However, the following issues need to be resolved before the manuscript can be considered for publication.

 

Major comments:

 

1.     Section3.2: First, in Line 211 the author indicate that the frequency is about 1.8 counts in some area. This an MHW in one year, how can the frequency be a decimal? I understand the values in Figure 4b should be either 1 or 2 or 3 here. Second, I guess the area of “weak intensity ring” has 2 counts of MHW with one has a very weak intensity. When average these two MHW events, there are rings pattern in the northeast corner in Figure 4d-f. In this situation, I suggest the author to separate the two MHW events, and only analyze the high intensity event.

 

 

2.     Section3.3: The author analyzes the mechanism of MHW in 2021 summer with MONTHLY mean atmospheric forcings. The MHW has a duration of DAYs, and from section 2.1.1, the daily atmospheric forcing data are also available. So, why not analyze atmospheric forcings in days during MHW (also, I am not sure whether there is a time lag between forcings and MHW, if yes, please consider it).

 

For the oceanic processes, the author considers the heat transport of geostrophic current. The MHW is the sea surface phenomenon, the Ekman current also contribute to the surface heat transport, it should be included here. Furthermore, the authors see an up to 2m/s velocity anomaly in the EKB, which is even much larger than the velocity of Kuroshio current.  I doubt it and please check the data.

 

Minor comments:

 

1.     Table1: the definition of Duration: ….“per year” to “per case”?

2.     Line 158: do you mean 0-10m heat content is calculated?

3.     Line 257: “bottom layer” to “subsurface” or ““lower layer””

Author Response

Please see the attachment.

Reviewer 2 Report

This manuscript analyzes Marine Heat Waves in the Japan/East Sea, with particular attention focused on the East Korean Bay. The authors examine trends over the past 40 years as well as the anomalous temperatures in the summer of 2021. They argue that the anomalous period in 2021 is likely due to characteristics associated with the atmosphere rather than lateral fluxes in the ocean. I agree with this conclusion. I do not have much experience with MHWs hence do not know if the trends they discuss are new observations. They do seem interesting and, given that they are likely due to atmospheric conditions these trends, especially near land, are likely to vary significantly from one region to the next so these may be new in that they are for a specific region. Hopefully, one of the other reviewers can address this. 

 

Although, as noted above, I found some of the results to be of interest, I have serious concerns with regard to the manuscript. These fall into two categories, one related to the presentation and the other to assumptions made and issues not addressed.

 

With regard to the presentation, I found the manuscript difficult to follow in a number of places. There are a number of grammatical issues, especially related to articles, ‘a’ and ‘the’, but this is not the most distracting. I found a number of the passages difficult to follow either because of the way the authors define certain quantities or because of the structure of the arguments. For example, to the best of my understanding, they define heat flux into the study area as positive along some boundaries and negative along others. If I have it right, this is very confusing. Another area of confusion relates to how they define frequency of MHW when discussing summer of 2021. The definition of frequency they give is # of MHW/year but in the summer of 2021, it is only one year so it is not clear how they end up with fractional numbers. It is also not clear to me how they define SST anomalies. My initial assumption was that it is the temperature minus the climatological mean but their discussion of temperatures in the summer of 2021 suggest that they may be defining it to be the observed temperature minus the threshold used to identify MHWs. I have detailed these as well as a number of other points of confusion - at least on my part - in the attached copy of the manuscript. 

 

I have not made editorial comments in the attached; I leave it to the editor to determine whether or not these should be addressed. The manuscript is readable it just requires a bit extra work on the part of the reader to sort through the grammatical anomalies. I would not feel comfortable submitting a paper in this shape but that’s me.

 

The biggest concern that I have with regard to issues related to the MHW time series relates to the depth of the anomalies they are seeing. I’m guessing that the majority of the events are related to diurnal warming (consistent with the high solar insolation and low winds in July 2021) and are relatively shallow. I would be surprised if many, especially the events that are only 5 to 10 days long extend much deeper than a few meters. As I mentioned above, I do not have expertise with the literature related MHWs so the distinction between shallow and deeper events may be well addressed in that literature. Regardless, I’m guessing that there are in situ measures of temperature with depth in this region (either Argo floats or specific studies) for 2021 and I think that the manuscript would benefit from including these data in their analysis. The authors argue at length about the impact of MHWs but my sense is that the extent of the impact will be a function of the depth of the events. 

 

Also of concern with regard to the trends is that the early period 1982-2002 is dominated by SST estimates from (IR) infrared sensors while post 2002 they include microwave SSTs. IR sensors do not ‘see’ through clouds while microwave sensors do. This means that estimates made prior to 2002 are biased toward clear sky conditions while those after 2002 are not. This does not appear to be an issue in that there is no apparent change in the trends as the microwave instruments come on-line but the authors might want to address it. Also, since they are focusing on MHWs, which are likely to occur under clear skies, the IR bias is not likely to be a serious problem but again, it is worth mentioning. Where the IR bias of the early period will likely play a role is in the calculation of the climatological temperatures, which will likely be biased high in periods generally susceptible to MHWs. This means that statistics of MHWs may tend to be lower on average for the same threshold used to define them than one would find if the climatology included all temperatures. This will, of course, not result in a trend since the same climatology is used for the entire period. As I recall, I found about a 0.2K positive bias in the temperatures of the western Sargasso Sea in the summer. 

 

 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.doc

Reviewer 3 Report

 

Review:

Characteristics and Drivers of Marine Heatwaves in 2021 summer in East Korea Bay, Japan/East Sea

 

General comments:

This paper presents an analysis of SST data and meteorological parameters in the context of Marine Heat Waves (MHW) in the Japan/East Sea. This paper is clearly written for the most part and succinctly presents a historical analysis of MHW in the area since 1982 along with a more detailed mechanistic analysis of MHWs in summer 2021. My main concerns are a lack of discussion and a lack of context.

 

The discussion section is very thin and I would elaborate more. I think more discussion of causal factors would be beneficial. Providing context in terms of MHWs in other regions would also be good. What are the causal factors behind MHWs in other regions? Is the EKB region unusual in this regard? Or, can MHWs here be easily compared to other regions? Was bathymetry considered? Why do MHWs often occur in the EKB? What is the outlook for the future? I would like to see a more detailed discussion of the results and analysis with more context with regard to MHW in other regions.

 

Specific comments:

Line 158: “we choose 10m above the sea surface as the reference depth to calculate the seawater heat content”. Shouldn’t this be 10m below the sea surface? If not, please explain the use of an above surface reference depth.

 

Lines 204 and 208: Caption of Figure 4. Please indicate which specific dates of each month were used. “July to August 2021” is ambiguous. Is it July 1^st  through August 31^st? Please put a specific date range there and in the text (line 208).

 

Line 235: I would rename this section title “Mechanistic Analysis of Extreme MHW Event in Summer 2021”

I would also give a bit more background on the “blocking high” that is mentioned several times. Is this a regular feature that is seen in most years? Was it particularly strong in 2021? In the conclusion, this is the main causal factor mentioned for the MHW in 2021, so a bit more background information is warranted in the “mechanistic analysis” section (3.3).

 

Line 236: I would say this: “Based on the above study, we analyze the causal mechanisms behind the MHW event in the EKB in summer 2021 from both atmospheric and oceanic perspectives.”

 

Line 278 (Figure 8). The colors used here and this panel in general are hard to see. I think more contrasting colors could be used. Overall, the individual plots are hard to see and interpret. Perhaps use less plots and only show maps every other day? Or, make a larger panel. These are too small.

 

Line 327: “MHWs are region-discrepant in the growth rates against a background trend of global MHWs notable enhancement”. I do not understand this sentence. Please revise and make clear what you are trying to say.

 

Line 329: “Our study finds that MHWs in the 2021 summer in EKB and its adjacent areas near the eastern coast increase significantly more than in other regions.” Again, this is unclear. The phrase “increase significantly more than in other regions” is problematic. Be more specific when describing “increase”. These areas show more MHW activity? I’m not sure what is increasing.

 

 

 

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have addressed most of my concerns. I have one more comment.

From the authors’ response I still don’t understand why the frequency (counts) of MHW in 2021 can be a fractional number. The definition of the FREQUENCY is the “Number of MHWs per year”, so when counting the numbers of MHWs in one year (2021 in this study), the counts should be an integer.

Author Response

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Author Response File: Author Response.docx