the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Jan 2025
Climate Oscillations influence on GOM Circulation
Abstract. Atmosphere-ocean interactions are understood to significantly modulate climate variability and ocean circulation patterns. In this study, the influence of climate oscillations, particularly the North Atlantic Oscillation (NAO) and the El Niño-Southern Oscillation (ENSO), on the circulation dynamics of the Gulf of Mexico (GoM) is investigated. Empirical Orthogonal Function (EOF) analysis was used to identify the principal modes of variability in the GoM circulation, and cross-spectral analysis was conducted to examine the coherence between the GoM circulation, NAO, and ENSO indices. The results reveal that Gulf of Mexico circulation patterns share significant frequencies with both NAO and ENSO. These shared frequencies suggest synchronization phenomena between NAO, ENSO, and the Atlantic Meridional Overturning Circulation (AMOC), indicating a strong influence of these climate oscillations on the GoM’s circulation. Key frequencies observed include a near 7-year period aligning with ENSO’s natural variability and semiannual periods linked to NAO and the Madden-Julian Oscillation (MJO). These climate oscillations are found to modulate heat transfer intensity in the GoM, influencing large-scale ocean-atmosphere interactions. The findings highlight the critical role of NAO-ENSO teleconnections in shaping GoM circulation variability and their broader implications for global oceanic heat transport mechanisms.
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Status: open (until 08 Mar 2025)
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RC1: 'Comment on esd-2024-38', Anonymous Referee #1, 29 Jan 2025
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This study investigates the influence of climate oscillations, particularly the North Atlantic Oscillation (NAO) and El Niño-Southern Oscillation (ENSO), on the circulation dynamics of the Gulf of Mexico (GoM). Using Empirical Orthogonal Function (EOF) and cross-spectral analysis, the authors identify shared frequencies and energy between GoM circulation and these climate indices, indicating strong teleconnections. The results suggest that these oscillations modulate heat transfer intensity in the GoM, influencing large-scale ocean-atmosphere interactions and contributing to global heat transport variability. This study presents a novel and interesting perspective on the connections between the Pacific Ocean, the Gulf of Mexico, and the Atlantic Ocean.
I have a few comments and questions:
- In line 70, what is the vertical structure of ORCA12? Can you give more details, especially about the top 200m used in this research?
- Can you explain why you selected only the first four modes (the summed contribution is slightly less than 50%)? Are the contributions of modes 5 and 6 similar to mode 4? Will adding mode 5 make the summed contribution exceed 50%?
- Can you provide more explanations of the spatial pattern of each mode? For example, the 1st mode represents the mean position of the Loop Current, as mentioned in the paper, but the meanings of the other modes are not described.
- For the applied EOF in Figure 1, it seems the EOF is normalized. What normalization is applied, or what unit are the PCs?
- In line 155, how did you determine that the 1.771y⁻¹ variance is due to MJO and not just a winter/summer shift?
- Could you provide more explanation of the rotating angle in Figure 1 and the phase in Figure 2? Specifically, which index is leading, and what is the time lag for each pair of indices?
Citation: https://doi.org/10.5194/esd-2024-38-RC1 -
CC1: 'Reply on RC1. Thank you for your thoughtful questions and interest in our study. We appreciate the opportunity to clarify key aspects of our work. Below, we address each of your questions point by point.', Gabriel Gallegos D.B., 13 Feb 2025
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- In line 70, what is the vertical structure of ORCA12? Can you give more details, especially about the top 200m used in this research?
The ORCA vertical configuration is set up in sigma coordinates and then interpolated in a z-coordinate system, where vertical resolution decreases with depth. In the upper 200m, the resolution varies from ~1m at the first levels to ~ 20m at the near 200m depth. This stricture ensures that surface circulation and climate-driven variability, are well solved. As the depth is increased the delta z is increased reaching ~200m at the deepest values. (included in new version at the attached manuscript) - Can you explain why you selected only the first four modes (the summed contribution is slightly less than 50%)? Are the contributions of modes 5 and 6 similar to mode 4? Will adding mode 5 make the summed contribution exceed 50%?
There is a minor computational discrepancy in the reported total variance. While the paper states that the first four modes describe 49.05% of the total variance, the sum of their contributions actually amounts to 51.83%. The fifth mode and further are not significant compared to the white noise EOF analysis ( horizontal line in PC graphic) - Can you provide more explanations of the spatial pattern of each mode? For example, the 1st mode represents the mean position of the Loop Current, as mentioned in the paper, but the meanings of the other modes are not described.
The paper describes EOF Mode 1 as representing the mean position of the Loop Current (LC), but additional clarification regarding the other modes is necessary:
EOF Mode 2 captures the Loop Current eddy-shedding process, where large warm-core anticyclonic eddies (Loop Current Eddies, LCEs) detach and drift westward into the central Gulf of Mexico (GoM).
EOF Mode 3 represents the westward propagation of Loop Current Eddies (LCEs) and their interaction with the deeper ocean circulation. Detached LCEs gradually lose energy as they interact with bottom topography.
EOF Mode 4, unlike the first three modes, which primarily describe LC structural changes, reflects variability induced by external forcing mechanisms, such as wind stress fluctuations. In this mode, LCEs appear less structured, and variability over the continental shelf becomes more significant.
(included in the new manuscript version) - For the applied EOF in Figure 1, it seems the EOF is normalized. What normalization is applied, or what unit are the PCs?
Kaiser Normalization was applied during the EOF analysis, scaling EOFs to unit variance. As a result, PCs were scaled accordingly to preserve the total variability, ensuring no artificial amplification. - In line 155, how did you determine that the 1.771y⁻¹ variance is due to MJO and not just a winter/summer shift?
The Madden-Julian Oscillation (MJO) and the seasonal winter-summer cycle are interconnected. While the seasonal cycle alone might explain some of the variance, the presence of a 1.771 cycles per year (cpy) spectral peak aligns with known MJO frequencies (~1.7-2.0 cpy). The MJO modulates intra-seasonal variability, either enhancing or reducing the strength of seasonal transitions depending on its phase and interaction with background climate modes.
Wu, M. L. C., Schubert, S. D., & Suarez, M. J. (2006). Seasonality and meridional propagation of the Madden–Julian Oscillation in a general circulation model. Journal of Climate, 19(10), 1901-1920. https://doi.org/10.1175/JCLI3680.1
Included in the new manuscript version - Could you provide more explanation of the rotating angle in Figure 1 and the phase in Figure 2? Specifically, which index is leading, and what is the time lag for each pair of indices?
Fig 1. The vector rotation represents the directional variability of the flow relative to the reference vector in the spatial variation map. This visualization shows how circulation patterns evolve over time. The rotation follows a geometric convention, where positive angles indicate counterclockwise from the east.
Fig2. The leading indices correspond to the dominant climate oscillations (ENSO, NAO, MJO). The time lag between each pair of indices is computed based on their cross-spectral phase relationship.
The computed time lags for ENSO-GoM and NAO-GoM interactions are included in the new manuscript version. Attached as supplement pdf file
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RC2: 'Reply on CC1', Anonymous Referee #1, 17 Feb 2025
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Thank you for your detailed and thoughtful responses to my comments. I appreciate the clarifications and the additional explanations you have provided. Your revisions effectively address my concerns, and the updated manuscript is now much clearer.
I have no further questions at this time, and I appreciate the effort you have put into refining the work.
Citation: https://doi.org/10.5194/esd-2024-38-RC2
- In line 70, what is the vertical structure of ORCA12? Can you give more details, especially about the top 200m used in this research?
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RC3: 'Comment on esd-2024-38', Anonymous Referee #2, 21 Feb 2025
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Employing statistical methods (EOF and cross-spectrum analyses), this study explored the circulation variability of the Gulf of Mexico (GoM) and its links to some global-scale climate variability (ENSO and NAO). While the results the author showed are interesting (in a specific time-scale, GoM and those climate indices are coherent), dynamical explanations are completely missing in the discussion. From my own point of view, this journal would expect insights into dynamics of the Earth system. Therefore, I am not satisfied with the current results. I would strongly recommend to investigate more insights into the dynamics.
Specific Comments:
Title: “GoM” is not very common, so better to say exactly “Gulf of Mexico” in the title.
Lines 27-31: It seems that this paragraph nicely summarizes the ocean current characteristics in the Gulf of Mexico and Yucatan Peninsula. If one figure summarizing geographical information of these current systems, readers can follow the statements here much more easily.
Line 33: wind-generate forcing should be “wind-forcing”
Line 34: atmospheric forcing of what?
Line 35: This upwelling is climatological phenomina? When I hear "event", that is a kind of anomalous variation like El Niño. If here the author state it like climatological characteristics, "event" should be deleted. Or something like "reinforced upwelling event"
Line 54-55: “NAO-driven….” This is not clear to me.
Line 111-112: perhaps, this paragraph is not necessary.
Figure 1: The EOF 3rd and 4th modes look very strange. The vectors are supposed to be ocean circulation, but why those are completely divergent? Is it possible? And, not clear what the color shows in Fig.1.
Lines 152-155. How MJO and EOF 1st mode can be connected? As I commented in the general part, some dynamical perspectives are necessary.
Citation: https://doi.org/10.5194/esd-2024-38-RC3 -
CC2: 'Reply on RC3', Gabriel Gallegos D.B., 26 Feb 2025
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We sincerely appreciate the reviewer’s insightful comments and their emphasis on the need for a deeper discussion of the dynamical links between the Gulf of Mexico (GoM) circulation and large-scale climate variability. Understanding these connections is indeed essential for providing a more comprehensive interpretation of the statistical results. In the following lines, each comment is carefully adressed with our most dedication.
Employing statistical methods (EOF and cross-spectrum analyses), this study explored the circulation variability of the Gulf of Mexico (GoM) and its links to some global-scale climate variability (ENSO and NAO). While the results the author showed are interesting (in a specific time-scale, GoM and those climate indices are coherent), dynamical explanations are completely missing in the discussion. From my own point of view, this journal would expect insights into dynamics of the Earth system. Therefore, I am not satisfied with the current results. I would strongly recommend to investigate more insights into the dynamics.
The following parragraphs are adressed to link the climate oscillations to the GoM circulation. (allready in the latest manuscript version)Line 171
One of the most direct physical arguments connecting ENSO to AMOC modulation points towards the modulation in Caribean pattern circulation changing sea surface height (SSH) (Huang et al., 2023), this circulation pattern modulation lead changes in heat distributon enhancing or weakening storms over the Atlantic and GoM (McPhaden, 2002), particularly during high meltwater flux periods (Orihuela-Pinto et al., 2022; Liu et al., 2014), more over as modulating the heat fluxes as part of the AMOC, this variability has a direct feedback to heat transport to the North Atlantic region, and potentially modulating NAO dynamics. The ocean-atmosphere feedback interactions have distinct timescale responses due the differences of density, specific heat and intrinsic properties (McPhaden, 2002), causing a natural lag and shift frecuencies and phases of oscillation for each coupled system.
Line 204The NAO-AMOC interactions have a geographically direct relationship. Positive NAO phases increase ocean-atmosphere heat flux and deep water formation, strengthening the AMOC (Hurrell et al., 2003; Delworth and Zeng, 2016). Negative NAO phases are expected to weaken the AMOC intensity. NAO’s influence on GoM circulation is more pronounced in lower frequencies for the most significant variability EOF first mode (42% described variability). However higher modes (less explained variability) show significant shared frequencies at seasonal periods. Shelf sea variability has strong seasonal frequency input, with wind dynamics winter (nortes) and summer (tropical storms). Both escenarios can be modulated by ENSO through atmospheric teleconnections (Mezzina et al., 2020; Feng et al., 2017).
Line 212
Climate oscillations can modulate the circulation of the Gulf of Mexico (GoM), which, in turn, plays a crucial role in advecting heat from the tropics to the North Atlantic. This process establishes a feedback loop between oceanic and atmospheric circulation, both of which are fundamental to global heat advection. As our understanding of these two primary heat distribution systems deepens, it becomes increasingly evident that climate oscillations are globally interconnected, either through atmospheric teleconnections or via the global ocean circulation (conveyor belt), which together function as the Earth’s principal mechanisms for heat redistribution.Specific Comments:
Title: “GoM” is not very common, so better to say exactly “Gulf of Mexico” in the title.
Title changed to: Climate Oscillations influence on Gulf of Mexico Circulation.
Lines 27-31: It seems that this paragraph nicely summarizes the ocean current characteristics in the Gulf of Mexico and Yucatan Peninsula. If one figure summarizing geographical information of these current systems, readers can follow the statements here much more easily.
Graphic added
Line 33: wind-generate forcing should be “wind-forcing”
changed for wind forcing
Line 34: atmospheric forcing of what?
I didnt recognize that in line 235 maybe it was line 235? . Eventhough text has changed.Line 35: This upwelling is climatological phenomina? When I hear "event", that is a kind of anomalous variation like El Niño. If here the author state it like climatological characteristics, "event" should be deleted. Or something like "reinforced upwelling event"
Changed to "upwelling pulses"
Line 54-55: “NAO-driven….” This is not clear to me.
Changed to: Possible interactions between the NAO-ENSO have been reported due to teleconnections, primarily through the modulation of upper-level atmospheric circulation. ENSO induces a Rossby wave train, which alters the Pacific Jet Stream, leading to subsequent changes in upper-level winds. These modifications impact large-scale weather patterns across both the Pacific and Atlantic basins,modulating NAO patterns
Line 111-112: perhaps, this paragraph is not necessary.
Deleted
Figure 1: The EOF 3rd and 4th modes look very strange. The vectors are supposed to be ocean circulation, but why those are completely divergent? Is it possible? And, not clear what the color shows in Fig.1.
The divergent/convergent patterns could be associated to the source or sinks of momentum derived from the cyclonic (source) and antycyclonic (sink) Loop Curren Eddies. https://doi.org/10.1029/2024AV001355
Lines 152-155. How MJO and EOF 1st mode can be connected? As I commented in the general part, some dynamical perspectives are necessary.
The connection between the MJO and the first EOF mode is influenced by ENSO, as subseasonal teleconnections from the MJO to North Atlantic-European (NAE) weather regimes strongly depend on the ENSO background state. During El Niño, the NAO+ regime teleconnection from MJO phases 1–5 is enhanced and persists longer, while during La Niña, the NAO− regime teleconnection from MJO phases 7–8 is strongest and occurs later. The ENSO circulation anomaly modifies MJO convection and Rossby wave generation, affecting teleconnection pathways to the NAE region. These interactions highlight the need for accurate subseasonal teleconnection representation in climate models. https://doi.org/10.1029/2019GL084683
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AC1: 'Reply on CC2', Alejandro Souza, 26 Feb 2025
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As you can see both cc comments really are author comments replying to reviewers. We hope this will suffice to resolve their queries
Alejandro Souza
Citation: https://doi.org/10.5194/esd-2024-38-AC1
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AC1: 'Reply on CC2', Alejandro Souza, 26 Feb 2025
reply
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CC2: 'Reply on RC3', Gabriel Gallegos D.B., 26 Feb 2025
reply
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NOC NEMO Output Delivered through JASMIN NOC Marine System Modelling group https://gws-access.jasmin.ac.uk/public/nemo/
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