Review Reports

Round 1

Reviewer 1 Report (New Reviewer)

This paper identifies the spatio-temporal characteristics of the Indo-Pacific Warm Pool and the corresponding rain pool. The authors find that both the warm and rain pools show significantly increasing trends on multidecadal timescales. They further find that ENSO plays a key role in modulating warm and rain pools on interannual timescales.

 

Overall, the paper is well written and analyzed. The findings on the synchronization between rain and warm pools are new, and the paper is acceptable. I have minor comments for the authors to improve their study.

 

1, The authors focus on the ENSO influence on the western Pacific warm pool at interannual timescales. In fact, at interannual timescales, other factors besides ENSO should also be discussed to describe the source of variability of the warm pool. A recent study [1] has identified a new signal, the SST in the southwest Pacific (SWP), which could influence the western Pacific warm pool and act as a useful predictor. This SWP warm SST anomaly signal may cause northerly winds south of the equator, resulting in lower wind speeds there and SST anomalies extending northward near the equator. Thus, the wind speed anomalies lead to changes in evaporation, which in turn lead to changes in warm pool SST in autumn. This cross-hemispheric progression of SST signals from the SWP to the warm pool is initiated and maintained by wind-evaporation-SST feedback, giving rise to an ocean memory effect, which shows considerable skills for climate prediction in the WTP six months in advance. This cross-hemispheric SST propogation explains more than 60% interannual variance in the warm pool variability and is independent of the ENSO signal. Therefore, this newly proposed mechanism should be discussed regarding the source of interannual variability of the warm pool.

 

2, The synchronization between rain and warm pools is interesting. However, the dynamics involved in this synchronization should be further discussed. In fact, associated with the warm pool warming or expansion, a Gill-type atmospheric response is generated due to the heating in the warm pool, and the surface pressure decreases. The lower surface pressure corresponds to the strengthening of upward motions and causes more precipitation in the warm pool [1].

 

References:

1, Cross-hemispheric SST propagation enhances the predictability of tropical western Pacific climate[J]. npj Climate and Atmospheric Science, 2022, 5(1): 1-8. https://doi.org/10.1038/s41612-022-00262-6

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

This study attempted to analyze the temporal variations of the Indo-Pacific warm pool (IPWP) and the associated Indo-Pacific rain pool (IPRP). The contents include long-term trends, seasonal variations, and interannual variations. A new aspect is the analysis of the relationship of IPWP and IPRP variations. However, there are several critical issues with the present version. In view of those issues, the current version is not suitable for acceptance and the recommendation is rejection with maybe resubmission.

 

Major comments:

1) The composite features of SST and rainfall during ENSO events have been analyzed in previous studies. The contents of section 3.3.2 do not provide new information and thus this part need to be deleted.

2) The analysis of section 3.3.3 for the 1997-1998 event does not provide new information as the temporal evolution of SST and rainfall for this event is known in the climate community. This part shall be removed as well.

3) It is hard to follow the comparison of the temporal variations of the IPWP among different datasets due to the differences in the temporal coverage and extracted main time periods of the components using the EMD method. For example, the 4.2-year component extracted based on the COBESST data and the 3.2-year component extracted based on the OISST data are on interannual time scales. However, how do the readers know they are consistent or not. The COBESST data has a 13-year component, but the OISST data has an 8-year component. Do they both represent interdecadal variations? But they have different time periods. The same time period components need to be extracted for comparison of the consistency in the temporal variations among the different datasets.

4) The temporal variations (for example, seasonal and interannual variations) and factors of the IPWP have differences for the western Pacific and the Indian Ocean sectors (Chi et al. 2017; Fasullo and Webster 1999; Kim et al. 2012; Wang et al. 2019). Thus, it is necessary to distinguish the two parts of the IPWP and IPRP in analyzing the relationship between IPWP and IPRP.

5) Although the authors claimed the coupling of IPWP and WPRP variations, only some superficial descriptions were provided and there were no analysis and interpretation of their relationship in the temporal evolution. This is a major weakness of this work. To understand their cause and effect, spatial-temporal relationship needs to be documented in detail, for example, by conducting a lead-lag correlation analysis. Unfortunately, the text descriptions provided by the authors, however, are mostly subjective without support of analysis of the cause-effect.

 

Suggestions for the authors:

1) Refine the comparison of the temporal evolutions of the IPWP among different datasets based on the components with nearly same time periods.

2) Add analysis in detail of the spatial and temporal relationship between IPWP and IPRP with reasonable physical interpretation of the cause and effect.

3) Remove the parts of analysis that has been presented in previous studies.

 

Chi J, Shi P, Zhuang W, Lin X, Cheng X, Du Y (2017) Heat budget of the western Pacific warm pool and the contribution of eddy heat transport diagnosed from HYCOM assimilation. J Oceanogr 73(2):1–11.

Fasullo J, Webster PJ (1999) Warm pool SST variability in relation to the surface energy balance. J Clim 12:1292–1305.

Kim ST, Yu JY, Lu MM (2012) The distinct behaviors of Pacifc and Indian Ocean warm pool properties on seasonal and interannual time scales. J Geophys Res Atmos 117:D05128.

Wang YQ, Wu R, Wen ZP (2019) Seasonal variations in size and intensity of the Indo-western Pacific warm pool in different sectors. J Oceanogr 75(5):423-439.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

This research is beneficial for multidisciplinary studies, where this research information can be used to analyze the coastal ecosystem health along the equatorial regions from broader perspectives. In addition, the Sustainability journal has targeted a wide range of readers' backgrounds (i.e., multi disciplines of researchers/academia, policymakers, etc.). However, the authors often use exclusive terms for climatologists/oceanographers. Therefore, It is necessary to modify some terms in order to make the paragraph more understandable. The authors also assume that all the readers are familiar with the "unit" utilized in the graph/map. Therefore, all figures show without a proper legend (i.e., without unit). For detail comments, please check the attached pdf. 

Comments for author File: Comments.pdf

Author Response

Thank you very much for your detailed suggestions and for pointing out some of the shortcomings in our considerations. We have made some changes according to your suggestions in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

This study explores the covariations of the warm pool and its corresponding wet atmospheric characteristics that are less studied. The novelty of this study seems sufficient, but several parts need to be modified, especially descriptions or explanations of the method used in this study is far lacking. Therefore, I suggest this paper should be under the “major revision” process. The detailed comments are as follows:

 

Overall, all the figures need to be carefully revisited. First, the number of figures is too much. The authors can reduce the number of figures by combining Figures 9 and 10 into one figure, and combining Figures 11, 12 and 13 into one figure. Second, the title of figures needs to be revised if exactly the same phrases are repeated for (a) and (b). Duplicates should be rejected. Third, the authors are responsible for visualizing figures by showing as many details as possible. Units and titles for legends or axes need to be added if needed. The continents, which are now colored in gray, should be changed to a darker color. There are statements in the manuscript regarding the name of places like “Bay of Bengal” or “Philippine Sea”. For readers’ understanding, I suggest adding one more figure to show the study area in Section 2.

 

The authors would carefully review the whole manuscript. Please make sure that full names are mentioned when the acronyms appear at first. The first alphabets of full names should be in capital letters.

 

1.     Introduction

-        Second paragraph of the Introduction section is too long as well as hard to get scope or point. It should be divided into two or more paragraphs.

-        Placing lines 63-70 as a separate paragraph would be better.

 

2.     Materials and Methods

-        A whole structure of this section seems weird. There’s no figure of study area. Data and method explanations are intermixed, which interrupts readers’ understanding.

-        I suggest the author to subdivide this section into “Study Area”, “Materials” and “Methods” respectively.

-        Lines 79-80: Why 4 monthly SST is considered in this study?

-        Placing lines 113-121 as a separate paragraph would be better. Please provide more descriptions of the methods including equations or flowchart for readers’ better understanding. This part should be highly elaborated.

-        The authors need to add why these two EEMD and SVD are chosen in this study. Please add the reason why the authors use both of these two methods not either of them.

 

3.     Results

-        Lines 156-159 should be moved to the end of previous paragraph.

-        Figure 3: I suggest you combining Figure 3(a) and (b) into one figure like add contour for the case of "before 1980s". You cannot draw like this because the spatial distribution should be different for each century. I suggest removing background colors (consisting of red and blue), and only leaving contours for each century to show the change of spatial distribution in time.

-        Line 178: What does “4 IPWP area timeseries” mean? Please elaborate more on this.

-        Line 179: How can readers figure out “significant decomposition signal results” from Figure 4?

-        Figure 4: Why the third and fourth panel of each four figures have different years? For example, third panel of Figure 4(a) shows the result of 4.5 years but that of Figure 4(b) is for 4.4 years.

-        Lines 232-233: How do readers know the expansion of the IOWP from Figure 7?

-        Lines 293-294: Why the phases selection criterion is five consecutive overlapping three-month-mean Nino-3 cross 0.8 standard deviations?

 

4.     Discussions

-        Lines 369-374 would be removed.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (New Reviewer)

I do not think that this work advances the current understanding of the climate variability relevant to ENSO and air-sea coupling. My previous comments are not addressed properly as stated in detail below.

1) My first and second comments regard the novelty of the anaysis about ENSO-related features in the tropical regions. While the authors removed the analysis about the 1997/98 El Nino event, the analysis of composite ENSO feature remain though they made a change in the category of the ENSO events. However, there is no comparison with previous studies about the consistency of the classification of the eastern and central Pacific ENSO events, e.g., Kao and Yu (2009, Journal of Climate, Vol. 22, No. 3, 615,-632). Kug et al. (2009, Journal of Climate, Vol. 22, No. 6,  1499-1513). More importantly, many of the obtained features of tropical SST, wind and precipitation anomalies have been presented in previous studies (e.g., Rasmusson and Carpenter (1982, Monthly Weather Review, Vol. 110, No. 5, 354-384) and the above two papers.

2) My third comment regards the consistency of the features obtained based on several SST datasets with different durations. The differences in the time periods of the extracted EMD modes make it difficult to claim consistency of the results among the different SST datasets. The authors did not do any analysis in this regard and thus the issue remains.

3) My fourth and fifth comments regard the physical relation between the SST and precipitation changes that may depend upon the region, say, the relation may differ for the Indian Ocean-western Pacific part from the central-eastern Pacific part. There are previous studies that demonstrate the different SST-precipitation relationship in the two parts. The authors simply claimed that the SST and precipitation pools are coupled without any illustration of how their variations are related to each other through what types of processes.

Overall, I am sorry to say that the paper is improper for acceptance for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

I have reviewed the revised manuscript and the authors' response.

Even though the authors have tried to address my comments, several concerns still remain. I'm quite worried that this paper is not ready to be reviewed in that Figures and added parts do not follow the fundamentals of research article.

First, equations in Lines 150-160, which have been added in this review round, do not have numbers. Therefore, the descriptions of Methodology including this part are highly illogical.

Second, Figure 1 has been added to show the difference between the characteristics of various types of UCEIs. However, the title "Polar plot of UCEI for 1982–2021." is really poor to explain the figure. The full description of figure should be elaborated in the title.

Besides of this figure, most figures do not satisfy my previous review comments. The authors are responsible for visualizing figures by showing as many details as possible. Units and titles for legends and axes need to be added to all the figures. The continents, which are now colored in gray, should be changed to a darker color. There are statements in the manuscript regarding the name of places like “Bay of Bengal” or “Philippine Sea”. For readers’ understanding, I suggest adding one more figure to show the study area with names of regions mentioned in the manuscript in Section 2.

Figure 7(a) and (b-e) cannot be combined in one figure. Please separate Figure 7 in to two figures (Figure 7(a) and Figure 7(b-e) individually).

A part of Figure 12 seems to be cut off. Please add figures carefully.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report (New Reviewer)

I have no more comments to give.

Reviewer 4 Report (New Reviewer)

Well revised. Thanks for the authors' effort.

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

See attached PDF file.

Comments for author File: Comments.pdf

Reviewer 2 Report

The manuscript examines the seasonal and interannual variabilities of the Indo–Pacific warm pool (IPWP), as well as the associated rain pool (IPRP), using TRMM Multi-Satellite Precipitation Analysis (TMPA) for the period 1998–2019. Unfortunately, all the findings have long been established, including the warming and expansion trend of the IPWP (Weller et al. 2016), the associated rainfall change (Xie et al., 2010), and the relationship between interannual variability of IPWP and ENSO (Wang and Enfield, 2003; Xie et al., 2005).

I recommend rejection of this paper for Sustainability publication because of the lack of novelty in the manuscript. In particular, some figures are repetitive to the authors’ previous paper on Remote Sensing (Yin et al., 2020; https://doi.org/10.3390/rs12071062). For example, the left panel Figure 5 and Figure 2 of Yin et al. (2020) are SAME! Figures 1e and 1f here and Figure 1 of Yin et al. (2020) are SAME, again! This is suspected to be self-plagiarism.

Therefore, they need to be revised by enhancing the discussion about the scientific content, and the structure of the results presentations to improve the quality of the paper. Multiple datasets can be involved. Significant findings should be reviewed, and appropriate references need to be used at the right places and properly discussed when necessary.

 

Reference

Wang, C. and Enfield, D.B., 2003. A further study of the tropical Western Hemisphere warm pool. Journal of climate, 16(10), pp.1476-1493.

Weller, E., Min, S.K., Cai, W., Zwiers, F.W., Kim, Y.H. and Lee, D., 2016. Human-caused Indo-Pacific warm pool expansion. Science advances, 2(7), p.e1501719.

Xie, S.P., Xu, H., Kessler, W.S. and Nonaka, M., 2005. Air–sea interaction over the eastern Pacific warm pool: Gap winds, thermocline dome, and atmospheric convection. Journal of Climate, 18(1), pp.5-20.

Xie, S.P., Deser, C., Vecchi, G.A., Ma, J., Teng, H. and Wittenberg, A.T., 2010. Global warming pattern formation: Sea surface temperature and rainfall. Journal of Climate, 23(4), pp.966-986.