the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Apr 2025
Synoptic observation of full mesoscale eddy lifetime and its secondary instabilities in the Gulf of Mexico
Abstract. Mesoscale eddies are crucial to ocean circulation, climate, and tracer transport. Yet, their full life cycle has never been observed synoptically at high resolution. In this study, we use novel SWOT satellite altimetry data to present the first synoptic characterization of a Loop Current Eddy's life cycle in the Gulf of Mexico, from formation to dissipation. SWOT allows for the direct observation of key dynamical processes—such as eddy shielding, high-mode instabilities, and dipolar interactions—that were previously only described in theoretical and numerical studies. These observations challenge the traditional view of eddies as simple, elliptical structures, emphasizing the role of mesoscale interactions in their evolution. Furthermore, SWOT captures intense submesoscale turbulence at the eddy's rim, revealing secondary instabilities likely driving its decay. These findings not only validate decades of vortex theory but also offer new insights into oceanic turbulence dynamics.
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Status: open (until 22 May 2025)
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RC1: 'Comment on egusphere-2025-1592', Anonymous Referee #1, 23 Apr 2025
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Review of “Synoptic observation of full mesoscale eddy lifetime and its secondary instabilities in the Gulf of Mexico” by Charly de Marez.
This is a concise, well written paper summarising observations of a loop current eddy’s life cycle in the Gulf of Mexico using high resolution altimetry from the relatively recently launched SWOT satellite. Direct observation of key dynamical processes such as eddy shielding, high-mode instabilities, and dipolar interactions were made possible by the resolution and coverage of the SWOT data. Although short and highly focused, this paper provides significant insight into processes which likely affect eddies throughout the global ocean. Some minor improvements to the text and figures are needed, but once completed I would recommend this paper for publication.
Comments on figures
All figures: the Ocean Science style guide says panel labels should be enclosed in brackets on the figure.
Figure 1:
I can see why you’ve chosen to display this the way you have – you get all of it on one figure, and the days you want to emphasise are larger. However, I think skipping between the larger and smaller panels does disrupt the flow for the reader because now you don’t just start at top left, work across the row, go down one row, work from left to right, etc. Given that you currently only have two figures in the whole paper, I suggest you consider stretching this out - perhaps three figures each with six panels of equal size, for example?
Are you sure the colour scale is colourblind-accessible? And personally, I find diverging colour scales which aren’t centered at zero rather confusing.
I think the AVISO SLA is maybe a bit too pale. For example, I really can’t see LCT1 on panel m, it just looks white. You could make the AVISO SLA quite a bit less pale while still maintaining a good contrast between it and the SWOT SLA.
Panels b, c, d, e, h, I, j, k, n, o, p, q have text above them which is far too small to read – I had to zoom in to 200% to see it was their dates. Since they’re not all regularly spaced in time, the reader needs to be able to see the dates. These panels also lack axes labels, and panels n and p have arrows which are not explained in the caption nor explicitly mentioned in the main text.
The labels LCE0, LCT0, LCE, VS, C1, C2, C3, C4 and LCT1 are not explained in the caption, nor have they been mentioned in the main text at the point where you first refer to this figure. I see that there’s a lot of explanation in the main text of these labels, and it’s understandable that you don’t want to put all of this in the caption, but perhaps you could say something like “The labels LCE0, LCT0, LCE, VS, C1, C2, C3, C4 and LCT1 will be discussed in the main text.”
You don’t need the colourbar three times on one figure, but you do need to label it.
Figure 2:
On figure 1, you said “The black contour marks the LCE detection from gridded altimetry, while thin gray contours represent iso-SLA lines from SWOT passes at 5 cm intervals”. Here on figure 2 you say “Black contours indicate iso-SLA lines from SWOT passes at 2 cm intervals”, but it looks like you still also have the black contour which is the LCE detection from gridded altimetry, even though this isn’t mentioned in the caption.
Panels a and d – is this exactly the same colour scale as in figure 1? It worth be worth either saying so in the caption, or altering the colourbar so it has the same tick marks as in figure 1, which will make it more obvious that it’s the same scale. In any case, the AVISO SLA is clearly not as pale here as on figure 1, and it would be better if the two figures were consistent.
Re the black contours which indicate iso-SLA lines from SWOT passes at 2 cm intervals – it looks like you’re only showing these in certain areas, i.e., outside the contour marking the LCE detection from gridded altimetry, but this isn’t stated in the caption.
Panels b and e show “Geostrophic current magnitude derived from the denoised SWOT SLA”, but you clearly have data outside the SWOT swaths. Ditto panels c and f.
In figure 1 your panel labels went left to right and then down to the next row. In figure 2 your panel labels go down the first column and then down the second column. It’s easier for the reader if you do them the same way in all figures. Ditto figure B1.
Panels b to f have no axes labels or visible tick marks. I think there are grid lines on all panels but they’re so faint they’re very difficult to see. Please make them like figure 1’s grid lines, and add axes labels. You don't need axes labels on all panels but you do need x-axis labels on the bottom row and y-axis labels on the left-hand column.
Figure B1:
The colourbars and length scale are very difficult to see, even zoomed in. Please put them outside the panels.
The text at the top of each panel is also quite small and hard to read.
The dashed and solid contours on panels e and f are difficult to see – maybe use a contrasting colour?
Textual comments
Line 52: “This newly formed eddy was then trapped within a train of alternating-polarity eddies (Figs. 1d-f).” To my eyes, Fig 1d doesn’t look that different to panels b or c, so it’s not clear to me at what point you would start describing something as “trapped within a train of alternating-polarity eddies”.
Line 128: Seagliders is a specific brand name, the generic term is ocean gliders.
Line 168: sutructures
Line 171: which gridded altimetric product? Even if you don’t want to show it, you could name it.
Line 173: SWOT measurements are not instantaneous. It takes time for the satellite to orbit around the globe. Perhaps you meant that the measurements are near-instantaneous compared to timescales of interest?
Line 174: “time gaps between passes remain too small to affect our conclusions.” Could you say a little more here about the timescales of interest? It is clear from figure 1 that changes do occur on weekly timescales.
Line 177: Fig 1l looks a lot like figure eleven in this journal’s typeface – you could miss the letter l out of your panel labels and just go j, k, m.
Line 188: “simulations are ran over a year.” This is bad grammar, please correct.
Line 190: “Timesteps are adjusted to respect the CFL criterion.” You don’t say what this criterion is, or what CFL stands for, or provide a reference.
Line 191: “the smallest as possible” – either “the smallest possible” or “as small as possible”. Plus “similarly as in” is bad grammar. Perhaps just “as small as possible (Callies et al., 2016).”
Line 192: delete “similarly”.
Line 204: “We chose R = 100km” because?
Citation: https://doi.org/10.5194/egusphere-2025-1592-RC1
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