On the role of domain aspect ratio in the westward intensification of wind-driven surface ocean circulation

Gianchandani, Kaushal; Gildor, Hezi; Paldor, Nathan

doi:https://doi.org/10.5194/os-17-351-2021

Articles | Volume 17, issue 1

https://doi.org/10.5194/os-17-351-2021

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

https://doi.org/10.5194/os-17-351-2021

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

Articles | Volume 17, issue 1

Research article

|

18 Feb 2021

Research article |

| 18 Feb 2021

On the role of domain aspect ratio in the westward intensification of wind-driven surface ocean circulation

Kaushal Gianchandani, Hezi Gildor, and Nathan Paldor

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Final revised paper (published on 18 Feb 2021)
Preprint (discussion started on 30 Sep 2020)

Interactive discussion

Status: closed

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

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RC1: 'Review of os-2020-93', Anonymous Referee #1, 27 Oct 2020
- AC1: 'Authors' response to RC1', Nathan Paldor, 29 Nov 2020
RC2: 'Review', David P. Marshall, 12 Nov 2020
- RC3: 'typographical correction', David P. Marshall, 13 Nov 2020
  - AC2: 'Authors' response to RC2 and RC3', Nathan Paldor, 29 Nov 2020
- AC2: 'Authors' response to RC2 and RC3', Nathan Paldor, 29 Nov 2020
EC1: 'Encourage revision', Katsuro Katsumata, 30 Nov 2020

Peer-review completion

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

AR by Nathan Paldor on behalf of the Authors (16 Dec 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Dec 2020) by Katsuro Katsumata

RR by David P. Marshall (04 Jan 2021)

Suggestions for revision or reasons for rejection

I find this a difficult recommendation as the appropriate option is not really available - which is that this requires an editorial decision. While the revisions have addressed most of my concerns and judged purely as a piece of GFD, I do believe the results are correct, I also remain unconvinced the results have much relevance to the ocean. If the paper is published, I would like this opinion to be recorded given that I have revealed my identity: this is the reason I have selected the option which allows me to enter comments in this box.

As I understand it, in the limit of large bottom friction, the curl of wind stress is largely compensated by the curl of the bottom friction over the basin interior, hence the reduction in the "effective Sverdrup transport" of the gyre. However, while realistic western boundary currents widths are around 50km, I am not aware of any evidence to support the idea that the Stommel mechanism is responsible for setting these boundary current widths. A plausible upper bound for the bottom drag coefficient in the Stommel model might be around $10^-7 {\rm s}^{-1}$, corresponding to a linear damping time scale of a few months and a Stommel boundary layer width of around $5 \, {\rm km}$. Hence I would estimate an upper bound for $\epsilon$ of around $10^{-3}$, significantly smaller than the smallest values shown in Figure 4. The results presented in this paper may well have some relevance to numerical ocean circulation models at 1 degree or coarser resolution, but that point is not made here.

So my recommendation is to either accept or reject the manuscript, depending on the inclination of the editor. If the manuscript is accepted, I would encourage the authors to insert a comment into the discussion to acknowledge that $\epsilon$ is likely rather small in reality, and therefore that the results might be most relevant to coarse resolution ocean models.

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ED: Publish subject to minor revisions (review by editor) (05 Jan 2021) by Katsuro Katsumata

AR by Nathan Paldor on behalf of the Authors (07 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (12 Jan 2021) by Katsuro Katsumata

AR by Nathan Paldor on behalf of the Authors (12 Jan 2021) Manuscript

Short summary

The classical theories of the western boundary currents, proposed in the first half of the 20th century, are extended to include cases of zonally elongated and meridionally narrow ocean basins. Results show for the first time that in basins that are sufficiently narrow meridionally, the equatorward wind-driven transport away from the western boundary is lower than that in meridionally wide basins. Our theoretical results are employed to explain the low transport in the East Australian Current.