The Loop Current: Observations of Deep Eddies and Topographic Waves

Hamilton, Pat B.; Bower, Amy; Furey, Heather H.; Leben, R. R.; Pérez-Brunius, Paula

doi:10.1175/jpo-d-18-0213.1

Cited by 30 publications

(19 citation statements)

References 40 publications

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“…However, the coupling mechanisms are more complicated than merely involving baroclinic instability and TRW propagation. For example, potential vorticity anomalies in the deep ocean induced by the upper-ocean perturbations can contribute to the coupling process as well (e.g., Donohue et al, 2008;Hamilton, 2009;Hamilton et al, 2019;Tenreiro et al, 2018), which is not analyzed in this study. Baroclinic Kelvin waves are Figure 17.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…It is implied that this mechanism is responsible for the coupling in the western GoM (Tenreiro et al, 2018). Moreover, other observational as well as numerical studies highlight the importance of both barotropic and baroclinic instability of the LC, the LCEs, and the LC front eddies (LCFEs) in the generation of lower‐layer cyclones and anticyclones (Chérubin et al, 2006; Donohue et al, 2016; Hamilton, Bower, et al, 2016; Hamilton et al, 2019; Hamilton, Lugo‐Fernández, et al, 2016; Hurlburt & Thompson, 1980; Oey, 1996, 2008; Xu et al, 2013). Atmospheric forcing (Welsh & Inoue, 2000) and topography are important factors in influencing the dynamics in the deep ocean as well (Cardona & Bracco, 2016; Donohue et al, 2008; Frolov et al, 2004; LaCasce, 1998).…”

Section: Introductionmentioning

confidence: 99%

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Coupling of the Surface and Near‐Bottom Currents in the Gulf of Mexico

Zhu

Liang

2020

JGR Oceans

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Coupling between the surface and near-bottom currents in the Gulf of Mexico (GoM) has been reported in many case studies. However, geographical variations of this coupling need more examination. In this study, surface geostrophic currents derived from satellite-observed sea surface height and subsurface currents from a collection of deep ocean moorings are used to examine the surface and bottom coupling in different parts of the GoM. The short-period (30-90 days) fluctuations generated by the Loop Current (LC) and the LC eddies (LCEs) have a more vertically coherent structure and stronger deep ocean expressions than the long-period fluctuations (>90 days). In addition, the strength of the coupling is modulated by the long-period variations of the LC and LCE sheddings. Moreover, the surface and bottom coupling varies geographically. In the LC region, the surface fluctuations along the eastern side of the LC are important in causing the bottom current fluctuations through baroclinic instability under the LC and through traveling topographic Rossby waves (TRWs) north of the LC. In the central deep GoM, the bottom currents are affected by the upper fluctuations of the northern LC through both local baroclinic instability and remote TRW propagation. In the northwestern GoM, the bottom current fluctuations are largely related to the remote surface variability from the west side of the LC by TRWs propagating northwestward. This study will help us better understand mechanisms of the bottom current fluctuations that are important for the dispersal of deep ocean materials and properties. Plain Language Summary Bottom currents in the Gulf of Mexico (GoM) are important in many ways, such as transporting fish larvae and spilled oil. However, in contrast to surface currents that are easily derived from the abundant satellite observations, our understanding of the bottom currents is very limited. In this study, the relationships between surface and near-bottom current fluctuations in different parts of the GoM are investigated by combining a collection of historical near-bottom current measurements and satellite data. The results show that the bottom current variability is linked to local processes such as current instability or remote processes through planetary wave propagation. The surface and bottom coupling is mainly related to the short-period variability generated along the Loop Current and the Loop Current eddies and has a significant influence on the bottom currents. Although the long-period fluctuations have weak bottom expressions, they can modulate the strength of the short-period coupling. Studying the coupling between the surface and bottom current fluctuations in the GoM can advance our understanding of mechanisms of the bottom currents that are important for the deep ocean ecosystem and industrial operations.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Coupling of the Surface and Near‐Bottom Currents in the Gulf of Mexico

Zhu

Liang

2020

JGR Oceans

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show abstract

“…Until recent decades, this concept was nullified by multiple deep-ocean observations, revealing considerable motions thousands of meters below the global ocean surface. For example, in the North Atlantic, low-frequency variability in the deep current with periods of several days to hundreds of days has been revealed (Thompson and Luyten 1976;Hogg 1981;Hamilton 1990;Pickart and Watts 1990;Peña-Molino et al 2012;Hamilton et al 2019); the deep western boundary current in the Southern Pacific is modulated by variability with a period of 10-50 days (Whitworth III et al 1999); and in the Indian Ocean's Mascarene Basin, deep water has large velocity fluctuations of 40-60 days (Quadfasel and Swallow 1986;Schär and Davies 1988;Warren et al 2002). In addition, a recent study in the South China Sea (SCS) reported that the temporal variability in the deep western boundary current is dominated by intraseasonal fluctuations by a period of approximately 90 days and that the amplitude of the deep western boundary current variability exceeds its mean value (Zhou et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Dynamics of the Baroclinic Rossby Waves Regulating the Abyssal South China Sea

Zhou

Zhao

et al. 2022

Journal of Physical Oceanography

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Intraseasonal fluctuation with periods of ∼90 days in the South China Sea (SCS) basin is investigated based on an array of 7 subsurface moorings. In the deep layer, the 90-day fluctuation is revealed to contribute significantly to the variability in the current, accounting for ∼69% of the subinertial variance. This fluctuation propagates westward along the mooring section with a phase speed of ∼4.6 cm s-1. In the upper layer, the fluctuation also propagates westward with a similar phase speed, but with opposite phase to that of the deep layer. These results suggest that the 90-day fluctuation regulating the abyssal SCS should be the first mode baroclinic Rossby wave. A set of experiments based on a two-layer dynamic model reveal that both the local wind-stress curl and the flow originating from the North Pacific through the Luzon Strait contribute to drive the 90-day fluctuation in the deep SCS, while the latter plays the dominant role.

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“…The other cyclones either do not experience a change in their KE or the change is presumably due to other processes such as vortex merging and splitting when KE and SSH variability are not correlated. The decay in KE of the LCFEs is presumably related to the conversion of energy into other motions such as topographic Rossby waves (LaCasce, ; Hamilton, ; Hamilton et al, ) and to dissipation through friction. The mechanism of LCFE intensification will be discussed in sections and .…”

Section: Resultsmentioning

confidence: 99%

Evidence of Loop Current Frontal Eddy Intensification Through Local Linear and Nonlinear Interactions with the Loop Current

2020

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During the 2010 Deepwater Horizon oil spill, an underestimated part of the oil was entrained into an intensified Loop Current Frontal Eddy (LCFE). These eddies, which are also known to play an essential role in the Loop Current eddy (LCE) shedding, are difficult to predict, and the dynamics involving their intensification are still not fully understood. The Loop Current (LC) and its strongest LCFEs were continuously tracked during 2009-2011 using sea surface height (SSH) from AVISO+. A mooring array provided complementary information about the internal structure of the LC-LCFE interaction. The intensification of the tracked LCFEs presented similar characteristics, independent of their location: a steep increase in kinetic energy, a corresponding negative increase in SSH, and an increase in its area. As the LCFE grows, the flow at the interface with the LC becomes stronger and deeper and the horizontal density gradient between the features increases. The intensification of the front and the LCFEs is driven by the advection (nonlinear) term and the gradient pressure (linear) term in the momentum budget. Evidence of an inverse energy cascade suggests that LCFEs are extracting energy and mass from the submesoscale field to the zone of contact between the LC and the LCFE, strengthening the front and allowing the LCFEs to grow during periods of intensification. Understanding the physics driving the LCFE intensification is a key step to improve LC forecast models and to better predict LCE shedding events, as well as oil and particle transport around the LC.

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The Loop Current: Observations of Deep Eddies and Topographic Waves

Cited by 30 publications

References 40 publications

Coupling of the Surface and Near‐Bottom Currents in the Gulf of Mexico

Coupling of the Surface and Near‐Bottom Currents in the Gulf of Mexico

Dynamics of the Baroclinic Rossby Waves Regulating the Abyssal South China Sea

Evidence of Loop Current Frontal Eddy Intensification Through Local Linear and Nonlinear Interactions with the Loop Current

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