Simulated zonal current characteristics in the southeastern tropical Indian Ocean (SETIO)

Ningsih, Nining Sari; Sakina, Sholihati Lathifa; Susanto, Raden Dwi; Hanifah, Farrah

doi:https://doi.org/10.5194/os-17-1115-2021

Articles | Volume 17, issue 4

https://doi.org/10.5194/os-17-1115-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-17-1115-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 4

Research article

|

23 Aug 2021

Research article |

| 23 Aug 2021

Simulated zonal current characteristics in the southeastern tropical Indian Ocean (SETIO)

Nining Sari Ningsih, Sholihati Lathifa Sakina, Raden Dwi Susanto, and Farrah Hanifah

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Final revised paper (published on 23 Aug 2021)
Preprint (discussion started on 12 Oct 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Major commments', Anonymous Referee #1, 03 Dec 2020
- AC1: 'Reply on RC1', Nining (N.S.) Ningsih, 15 Jan 2021
RC2: 'Comment to Zonal Current Characteristics in the Southeastern Tropical Indian Ocean (SETIO) os-2020-91', Anonymous Referee #2, 10 Dec 2020
- AC2: 'Reply on RC2', Nining (N.S.) Ningsih, 15 Jan 2021
AC1: 'Reply on RC1', Nining (N.S.) Ningsih, 15 Jan 2021

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Nining (N.S.) Ningsih on behalf of the Authors (05 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (17 Feb 2021) by Viviane Menezes

RR by Anonymous Referee #2 (06 Mar 2021)

Suggestions for revision or reasons for rejection

Review on “Simulated zonal Current Characteristics in the Southeastern Tropical Indian Ocean (SETIO)” [Paper # os-2020-91]

This study investigates the variability of zonal current within the region that involves multiple currents system, i.e., the South Java Current, the Indonesian Throughflow, the South Equatorial Current, and the coastal upwelling. Due to interactions among these currents, the variability in this region is very complex. Using EOF and EEMD, the authors have discussed the intraseasonal, seasonal, and interannual variations of the zonal currents in the southeastern tropical Indian Ocean. The authors have improved their manuscript, the results are reasonable and the text are generally easy to follow. I think this study basically meets the goals of the Journal, and thus should be accepted after some major revision, as listed below.

Major comments:
1. Although the authors explained why they have done EEMD after EOF, there are some issues need to be further clarified. First, what are the physical mean of the EOF1? In other words, the EOF1 spatial mode is subject to multi-time scale variations, making it confusing that which dynamical processes are dominant.
2. The mesoscale eddies are very active in the study area, I think it should be important for the zonal current variations at intraseasonal to semi-annual time scale. Can the EOF analysis able to resolve the contribution of eddies? I strongly encourage the authors to discussion focus on this point of view in detail.
3. The relationship between IOD and zonal currents lies in two aspects: 1) the IOD SST anomaly induces surface wind anomalies, together with SSH gradient, resulting in zonal currents anomalies; and 2) Oceanic long waves dynamics (i.e. the Kelvin and Rossby waves) propagation may induce zonal currents anomalies and SSH anomalies in the southeastern tropical Indian Ocean, thereby resulting in IOD events. In addition, since the IOD tend to co-occur with ENSO, partial correlation is recommended to use, rather than correlation analysis.
4. It is interesting that the zonal currents are correlated with remote winds in both equatorial Indian and Pacific oceans, but the explanation for the dynamical links are weak. Why the zonal currents lag the Pacific winds by 4 months? What is the pathways for the Pacific signal?

Specific comments
1. In section 2, Line 100-105, it should better be ‘Data and Methods’, instead of ‘Material and Methods’
2. For the validation of the HYCOM data, it is better to calculate the root mean square errors as well.
3. I think it is necessary to introduce the time interval of the HYCOM data that used for the analysis, is it daily or monthly mean? If it is daily averaged, it may hard to resolve intraseasonal signal.
4. Line 134, since the EOF has been introduced in Introduction, so it does not necessary to repeat the full name ‘Empirical Orthogonal Function’ here.
5. It should also introduce the method for calculating the power spectrum.

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RR by Anonymous Referee #1 (11 Mar 2021)

Suggestions for revision or reasons for rejection

I am grateful to the authors for their efforts in improving the manuscript. Most of my previous concerns have been addressed. But I have some further comments for your reference. I agree with another anonymous review that this manuscript failed to specify clearly what the novelty of this work is for the scientific community. The authors presented plenty of analysis and estimates based on their simulations, which I think is a good contribution to the community. But unfortunately, it seems that the poor writing and cumbersome structure of the present version make the manuscript a hard read. I suggest the authors further to revise and refine the article carefully. My comments are listed below.

Abstract: The authors may clarify clearly what is new relative to previous studies. Remove less important or uninspiring conclusions from the Abstract and add important or novel conclusions to it. For example, the readers may don’t care about the power density of each time scale in the Abstract.
Lines 190-205: I feel confused about this paragraph. The authors claimed that the SJC and SJUC are caused by downwelling Kelvin waves, but you concluded that the SJC and SJUC are induced by local eastward wind as well and called the downwelling Kelvin waves a minor addition. Then, who is the real cause of the currents? Meanwhile, I don’t understand how can a non-stationarity wave forms a steady mean flow?
Line 44: simulated data -> simulations
Line 50: delete “by previous investigators”
Line 61: interannual variability of what?
Line 63: delete “event”
Line 75: with -> on a
Lines 79-80: The statement is too absolute to say “no information concerning”. You may rephrase this sentence, for example: “However, the seasonal and interannual variations of SEC in the SETIO is unclear yet.”
Line 82: all previous investigations -> previous studies
Line 185: seasonal depth profiles -> seasonal mean profiles
Line 187: at the nine observation points -> at each point
Line 188 and elsewhere: used too many “distinctive”
Figure 4: add unit of longitudes
Figures 5 and 9: add unit of latitudes
Figures 10-12: could you estimate the proportion of contribution of each EEMD mode to the EOF1? For example, standard deviation of each EEMD mode relative to the total variance of PC1?

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ED: Reconsider after major revisions (27 Mar 2021) by Viviane Menezes

AR by Nining (N.S.) Ningsih on behalf of the Authors (05 May 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (24 May 2021) by Viviane Menezes

RR by Anonymous Referee #2 (15 Jun 2021)

RR by Anonymous Referee #1 (15 Jun 2021)

ED: Publish subject to technical corrections (02 Jul 2021) by Viviane Menezes

Dear Dr. Ningsih,

We have received the two reviews of your MS entitled "Simulated Zonal Current Characteristics in the Southeastern Tropical Indian Ocean (SETIO)." Both reviewers agree that the new version is suitable for publication in Ocean Sciences, and all their concerns have been addressed, although one of them found the abstract too long. I have taken a quick look at the revised MS and agree with the reviewers-- the MS is much improved, but the abstract is excessive length. Generally, abstracts have between 150-300 words, and yours have 527. Also, there are too many acronyms.

Please take a look at the recommendation from the OSD website: "Abstract: the abstract should be intelligible to the general reader without reference to the text. After a brief introduction of the topic, the summary recapitulates the key points of the article and mentions possible directions for prospective research. Reference citations should not be included in this section unless urgently required, and abbreviations should not be included without explanations. An abstract should be short, clear, concise, and written in English with correct spelling and good sentence structure."

Thus, I am recommending the MS for publication subject to technical corrections. The abstract must be shortened. Also, in the Introduction, two phrases in sequence (L#58-L#60) start with "Meanwhile" which makes the text a bit hard to understand. The authors may want to fix this issue as well.

L#58-60: Meanwhile, 60-day variations are the dominant feature in the SJUC, which are forced by intraseasonal atmospheric variability associated with the eastward movement of the Madden-Julian Oscillation (MJO) over the eastern equatorial Indian Ocean. Meanwhile, seasonal variabilities of SJC and SJUC those exist along the coasts of western Sumatra and southern Java have been investigated based on observation data (e.g., Sprintall et al., 1999; 2010; Qu and Meyers, 2005).

I look forward to receiving the revised manuscript soon.

Best regards,

Viviane Menezes

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AR by Nining (N.S.) Ningsih on behalf of the Authors (07 Jul 2021) Author's response Manuscript

Short summary

Detailed ocean currents in the southeastern tropical Indian Ocean have not been fully explained because of limited observations. Here, zonal current characteristics in the region have been studied using 64-year HYCOM results (1950–2013). This study has revealed distinctive features of current variations on various timescales. Current vertical structures, their responses to remote forcings from the Pacific and Indian oceans, and contributions of each timescale have all been investigated.