Connecting flow–topography interactions, vorticity balance, baroclinic instability and transport in the Southern Ocean: the case of an idealized storm track

Jouanno, Julien; Capet, Xavier

doi:https://doi.org/10.5194/os-16-1207-2020

Articles | Volume 16, issue 5

https://doi.org/10.5194/os-16-1207-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/os-16-1207-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 5

Research article

| Highlight paper

|

20 Oct 2020

Research article | Highlight paper |

| 20 Oct 2020

Connecting flow–topography interactions, vorticity balance, baroclinic instability and transport in the Southern Ocean: the case of an idealized storm track

Julien Jouanno and Xavier Capet

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Final revised paper (published on 20 Oct 2020)
Preprint (discussion started on 04 Feb 2020)

Interactive discussion

Status: closed

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

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RC1: 'Review report', Anonymous Referee #1, 17 Mar 2020
- AC1: 'Response to reviewer #1', Julien Jouanno, 29 Jun 2020
RC2: 'An interesting hypothesis and model experiments in need of more robust arguments.', Anonymous Referee #2, 31 Mar 2020
- AC2: 'Response to reviewer #2', Julien Jouanno, 29 Jun 2020

Peer-review completion

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

AR by Anna Wenzel on behalf of the Authors (01 Jul 2020) Author's response

ED: Referee Nomination & Report Request started (17 Jul 2020) by Neil Wells

RR by Anonymous Referee #2 (04 Aug 2020)

Suggestions for revision or reasons for rejection

In this revised manuscript the authors have done a good job at responding to the comments of both myself and Reviewer 1. The paper remains enjoyable and the revisions have improved its clarity. Where they have declined to act upon a reviewers’s comment, the authors have given a good explanation in their response. I have added a few minor comments below that the authors may wish to address. However, there is no reason why these would require another round of review.

There are some interesting questions remaining, which I hope to see the authors take up in future publications. In particular, it would be interesting to explore the how roughness characteristics, such as the variance of the bottom height and horizontal scale, interact with the dynamics of the ACC. The authors have concentrated on eddy saturation in this paper, but I see potential for bottom roughness to also impact upon eddy compensation (reduced sensitivity of the residual MOC to wind stress). Whether sufficient roughness can offset the need for high bathymetry in eddy saturation scenarios would also be interesting, given some of the results of their earlier work (Jouanno et al., 2016).

Minor Comments

lines 82, 83, 107, etc : As noted by Reviewer 1, in a few places the authors continue to use notation of the form 2.10-4, rather than the standard form of 2x10-4.

line 125 : “with p_b the pressure”, don’t need the with at this point.

line 140-144 : The transport of Abernathey & Cessi’s (2014) flat bottomed configuration is mentioned here, but not that of their configuration with a ridge (~70Sv, from eyeballing their Figure 8). Other model with ridges produce similar transports, ~90Sv, such as those in Munday et al. (2015) and Marshall et al. (2017).

line 161 : I would say that bottom roughness forces near zero flow at the bottom. In Figure 4 we can see that it isn’t quite zero. I imagine there is potential for quite a lot of spatial variation in the bottom flow too. It might be worth reinforcing that it is both the mean and eddying flow that is near zero.

line 268 : confined TO THE east

line 284 : manifestation OF baroclinic instability

line 286 : mean state leadS to negative

line 290-296 : An important caveat to mention regarding Constantinou et al. (2019) is that the regime in which their results indicate barotropic saturation is unlikely to apply to the real Southern Ocean.

Section 4.2 : An extremely relevant reference to this section is Youngs et al. (2017). This paper looks at the energetics of meanders in great detail, highlighting that barotropic energy (conversions) are important to their dynamics and that baroclinic instability is insufficient to do so.

lines 326-333 : The experiments of Marshall et al. (2017), which the authors cite elsewhere, also investigate the role of bottom friction and its role in eddy saturation.

References

Jouanno, J., X. Capet, G. Madec, G. Roullet, and P. Klein, 2016: Dissipation of the energy imparted by mid-latitude storms in the southern ocean. Ocean Sci., 12, 743–769, doi:10/5194/os–12–743–2016.

Munday, D. R., H. L. Johnson, and D. P. Marshall, 2015: The role of ocean gateways in the dynamics and sensitivity to wind stress of the early Antarctic Circumpolar Current. Paleoceanography, 30, 284–302, doi:10.1002/2014PA002675.

Youngs, M. K., A. F. Thompson, A. Lazar, and K. J. Richards, 2017: ACC meanders, energy transfer and mixed barotropic-baroclinic instability. J. Phys. Oceanogr., 47, 1291–1305, doi:10.1175/JPO–D–16–0160.1.

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ED: Publish subject to technical corrections (14 Aug 2020) by Neil Wells

AR by Julien Jouanno on behalf of the Authors (18 Aug 2020) Author's response Manuscript

Short summary

The dynamical balance of the Antarctic Circumpolar Current and its implications on the functioning of the world ocean are not fully understood and poorly represented in global circulation models. In this study, the sensitivities of an idealized Southern Ocean (SO) storm track are explored with a set of eddy-rich numerical simulations. We show that the classical partition between barotropic and baroclinic modes is sensitive to current–topography interactions in the mesoscale range of 10–100 km.