Loop Current Cycle: Coupled Response of the Loop Current with Deep Flows

Abstract Although the upper-layer dynamics of the Loop Current and eddies in the Gulf of Mexico are well studied, the understanding of how they are coupled to the deep flows is limited. In this work, results from a numerical model are analyzed to classify the expansion, shedding, retraction, and deep-coupling cycle (the Loop Current cycle) according to the vertical mass flux across the base of the Loop. Stage A is the “Loop reforming” period, with downward flux and deep divergence under the Loop Current. Stage B is the “incipient shedding,” with strong upward flux and deep convergence. Stage C is the “eddy migration,” with waning upward flux and deep throughflow from the western Gulf into the Yucatan Channel. Because of the strong deep coupling between the eastern and western Gulf, the Loop’s expansion is poorly correlated with deep flows through the Yucatan Channel. Stage A is longest and the mean vertical flux under the Loop Current is downward. Therefore, because the net circulation around the abyssal basin is zero, the abyssal gyre in the western Gulf is cyclonic. The gyre’s strength is strongest when the Loop Current is reforming and weakest after an eddy is shed. The result suggests that the Loop Current cycle can force a low-frequency [time scales ∼ shedding periods; O(months)] abyssal oscillation in the Gulf of Mexico.

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The Flow through the Gulf of Mexico

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0189.1 ◽

2019 ◽

Vol 49 (6) ◽

pp. 1381-1401 ◽

Cited By ~ 3

Author(s):

J. Candela ◽

J. Ochoa ◽

J. Sheinbaum ◽

M. López ◽

P. Pérez-Brunius ◽

...

Keyword(s):

Gulf Of Mexico ◽

Straits Of Florida ◽

The North ◽

Astronomical Tide ◽

Flow Through ◽

Sverdrup Transport ◽

The Mean ◽

Yucatan Channel ◽

Range Variation

AbstractFour years (September 2012 to August 2016) of simultaneous current observations across the Yucatan Channel (~21.5°N) and the Straits of Florida (~81°W) have permitted us to investigate the characteristics of the flow through the Gulf of Mexico. The average transport in both channels is 27.6 Sv (1 Sv = 106 m3 s−1), in accordance with previous estimates. At the Straits of Florida section, the transport related to the astronomical tide explains 55% of the observed variance with a mixed semidiurnal/diurnal character, while in the Yucatan Channel tides contribute 82% of the total variance and present a dominant diurnal character. At periods longer than a week the transports in the Yucatan and Florida sections have a correlation of 0.83 without any appreciable lag. The yearly running means of the transport time series in both channels are well correlated (0.98) and present a 3-Sv range variation in the 4 years analyzed. This long-term variability is well related to the convergence of the Sverdrup transport in the North Atlantic between 14.25° and 18.75°N. Using 2 years (July 2014–July 2016) of simultaneous currents observations in the Florida section, the Florida Cable section (~26.7°N), and a section across the Old Bahama Channel (~78.4°W), a mean northward transport of 28.4, 31.1, and 1.6 Sv, respectively, is obtained, implying that only 1.1 Sv is contributed by the Northwest Providence Channel to the mean transport observed at the Cable section during this 2-yr period.

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A Lagrangian approach to the Loop Current eddy separation

Nonlinear Processes in Geophysics ◽

10.5194/npg-20-85-2013 ◽

2013 ◽

Vol 20 (1) ◽

pp. 85-96 ◽

Cited By ~ 16

Author(s):

F. Andrade-Canto ◽

J. Sheinbaum ◽

L. Zavala Sansón

Keyword(s):

Numerical Model ◽

Gulf Of Mexico ◽

Caribbean Sea ◽

Separation Process ◽

Sea Surface ◽

Loop Current ◽

Hyperbolic Point ◽

Finite Time Lyapunov Exponents ◽

Florida Straits ◽

Strain Direction

Abstract. Determining when and how a Loop Current eddy (LCE) in the Gulf of Mexico will finally separate is a difficult task, since several detachment re-attachment processes can occur during one of these events. Separation is usually defined based on snapshots of Eulerian fields such as sea surface height (SSH) but here we suggest that a Lagrangian view of the LCE separation process is more appropriate and objective. The basic idea is very simple: separation should be defined whenever water particles from the cyclonic side of the Loop Current move swiftly from the Yucatan Peninsula to the Florida Straits instead of penetrating into the NE Gulf of Mexico. The properties of backward-time finite time Lyapunov exponents (FTLE) computed from a numerical model of the Gulf of Mexico and Caribbean Sea are used to estimate the "skeleton" of flow and the structures involved in LCE detachment events. An Eulerian metric is defined, based on the slope of the strain direction of the instantaneous hyperbolic point of the Loop Current anticyclone that provides useful information to forecast final LCE detachments. We highlight cases in which an LCE separation metric based on SSH contours (Leben, 2005) suggests there is a separated LCE that later reattaches, whereas the slope method and FTLE structure indicate the eddy remains dynamically connected to the Loop Current during the process.

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Transports through the Straits of Florida

Journal of Physical Oceanography ◽

10.1175/jpo-2688.1 ◽

2005 ◽

Vol 35 (3) ◽

pp. 308-322 ◽

Cited By ~ 43

Author(s):

Peter Hamilton ◽

Jimmy C. Larsen ◽

Kevin D. Leaman ◽

Thomas N. Lee ◽

Evans Waddell

Keyword(s):

Gulf Of Mexico ◽

North Atlantic Ocean ◽

Florida Current ◽

Loop Current ◽

Straits Of Florida ◽

Key West ◽

The North ◽

Side Channels ◽

Yucatan Channel ◽

Accurate Indicator

Abstract Transports were calculated for four sections of the Florida Current from Key West to Jupiter, Florida, using a moored current-meter array and voltages from cross-channel telephone cables at the western and northern ends of the Straits of Florida. In addition, moored arrays were used to estimate transport through the Northwest Providence, Santaren, and Old Bahama Channels that connect the Florida Current to the southwestern part of the North Atlantic Ocean. Transport measurements were obtained for an 11-month period from December 1990 to November 1991. Mean transports of ∼25 Sv (1 Sv ≡ 106 m3 s−1) for the flow across the western ends of the straits, which agree quite well with recent estimates of 23.8 ± 1 Sv entering the Gulf of Mexico through the Yucatan Channel, were obtained from both the Key West to Havana cable and the moored array. This estimate is about 5 Sv less than the generally accepted transport through the northern end of the straits at 27°N. This difference was partially accounted for by inflows through the side channels with more transport from the Old Bahama than the Northwest Providence Channel. The variability in the southern part of the straits was larger than at 27°N and included large diversions of the Florida Current south of the Cay Sal Bank and into the Santaren Channel that were caused by large meanders of the flow. The variability of transport in the side channels contributed to the variability of the Florida Current and reduces the correlations of the transports at the ends of the straits. Therefore, the well-measured transport at 27°N is not an accurate indicator of the transport of the Loop Current out of the Gulf of Mexico.

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Deep Cyclonic Circulation in the Gulf of Mexico

Journal of Physical Oceanography ◽

10.1175/jpo2790.1 ◽

2005 ◽

Vol 35 (10) ◽

pp. 1801-1812 ◽

Cited By ~ 40

Author(s):

Christopher J. DeHaan ◽

Wilton Sturges

Keyword(s):

Gulf Of Mexico ◽

Accurate Result ◽

Sea Water ◽

Cyclonic Circulation ◽

Loop Current ◽

Mean Flow ◽

Eastern Gulf Of Mexico ◽

Geostrophic Shear ◽

Layer Flow ◽

Yucatan Channel

Abstract The anticyclonic Loop Current dominates the upper-layer flow in the eastern Gulf of Mexico, with a weaker mean anticyclonic pattern in the western gulf. There are reasons, however, to suspect that the deep mean flow should actually be cyclonic. Topographic wave rectification and vortex stretching contribute to this cyclonic tendency, as will the supply of cold incoming deep water at the edges of the basin. The authors find that the deep mean flow is cyclonic both in the eastern and western gulf, with speeds on the order of 1–2 cm s−1 at 2000 m. Historical current-meter mooring data, as well as profiling autonomous Lagrangian circulation explorer (PALACE) floats (at 900 m), suggest that vertical geostrophic shear relative to 1000 m gives a surprisingly accurate result in the interior of the basin. The temperature around the edges of the basin at 2000 m is coldest near the Yucatan Channel, where Caribbean Sea water is colder by ∼0.1°C. The temperature increases steadily with distance in the counterclockwise direction from the Yucatan, consistent with a deep mean cyclonic boundary flow.

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Mean Flow in the Gulf of Mexico

Journal of Physical Oceanography ◽

10.1175/2007jpo3802.1 ◽

2008 ◽

Vol 38 (7) ◽

pp. 1501-1514 ◽

Cited By ~ 16

Author(s):

Wilton Sturges ◽

Kern E. Kenyon

Keyword(s):

Gulf Of Mexico ◽

Data Sources ◽

Loop Current ◽

Independent Data ◽

Ekman Pumping ◽

Mean Flow ◽

The West ◽

Net Flux ◽

Yucatan Channel ◽

Current Potential

Abstract Several independent data sources suggest that there is a net upper-layer mass flux O(3 Sv) (Sv ≡ 106 m3 s−1) to the west in the central Gulf of Mexico, even though the western gulf is a closed basin. A plausible explanation is that this net flux is pumped downward by the convergent wind-driven Ekman pumping, as is typical of all midlatitude anticlyclonic gyres. The downward flux can follow isopycnals to depths O(500–600 m) and deeper by eddy mixing; a mechanism for forcing deep water to the south through the Yucatan Channel is provided by the intrusion and ring-shedding cycle of the Loop Current. Potential vorticity maps show that a deep flow from the western gulf back to the Yucatan Channel is likely.

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An Analysis of Loop Current Frontal Eddies in a ⅙° Atlantic Ocean Model Simulation

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0227.1 ◽

2013 ◽

Vol 43 (9) ◽

pp. 1924-1939 ◽

Cited By ~ 10

Author(s):

Haosheng Huang ◽

Nan D. Walker ◽

Ya Hsueh ◽

Yi Chao ◽

Robert R. Leben

Keyword(s):

Numerical Model ◽

Atlantic Ocean ◽

General Circulation ◽

Model Simulation ◽

Ocean Model ◽

Anticyclonic Eddy ◽

Loop Current ◽

Particle Tracking Method ◽

The Caribbean ◽

Yucatan Channel

Abstract The Loop Current frontal eddies (LCFEs) refer to cyclonic cold eddies moving downstream along the outside edge of the Loop Current in the eastern Gulf of Mexico. They have been observed by in situ measurements and satellite imagery, mostly downstream of the Campeche Bank continental shelf. Their evolution, simulated by a primitive equation ⅙° and 37-level Atlantic Ocean general circulation numerical model, is described in detail in this study. Some of the simulated LCFEs arise, with the passage through the Yucatan Channel of a Caribbean anticyclonic eddy, as weak cyclones with diameters less than 100 km near the Yucatan Channel. They then grow to fully developed eddies with diameters on the order of 150–200 km while moving along the Loop Current edge. Modeled LCFEs have a very coherent vertical structure with isotherm doming seen from 50- to ~1000-m depth. The Caribbean anticyclone and LCFE are two predominant features in this numerical model simulation, which account for 22% and 10%, respectively, of the short-term (period less than 100 days) temperature variance at 104.5 m in the complex empirical orthogonal function (CEOF) analysis. The source water inside the LCFEs that are generated by Caribbean anticyclonic eddy impingement can be traced back, using a backward-in-time Lagrangian particle-tracking method, to the western edge of the Caribbean Current in the northwest Caribbean Sea and to coastal waters near the northern Yucatan Peninsula. The model results indicating a pairing of anticyclonic and cyclonic eddies within and north of the Yucatan Channel are supported by satellite altimetry measurements during February 2002 when several altimeters were operational.

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Energetics and Kinematics of Inertial Oscillations in the Central Northern GOM

10.4043/31020-ms ◽

2021 ◽

Author(s):

Leonid Ivanov ◽

Rafael Ramos ◽

Drew Gustafson

Keyword(s):

Gulf Of Mexico ◽

Water Column ◽

Low Frequency ◽

Mode Shapes ◽

Loop Current ◽

Inertial Waves ◽

Energy Propagation ◽

Inertial Oscillations ◽

Wide Range ◽

Inertial Currents

Abstract Understanding the physics of generation, propagation, and dissipation of inertial currents is important from a variety of aspects. For the Gulf of Mexico, one such aspect is that these oscillations represent an uncertainty in the measurements and forecasting of the longer-period currents, such as those due to the Loop Current (LC) and meso-scale eddies. The Industry has a practice of applying an ‘uplift’ to estimates of current velocity to account for the effect of tidal and inertial currents in cases when observations or model estimates do not resolve the high-frequency current variability. The value of the ‘uplift’ is assumed to be proportional to the intensity of the low-frequency flow. Our analysis aims at testing whether this assumption is valid by providing a detailed description of the space-time variability, including seasonal changes, of inertial oscillations in the central northern Gulf of Mexico. From the analysis of long-term current profile observations and drifter data we found that, on average, near-inertial oscillations have higher amplitudes outside of the areas of strong low-frequency currents associated with a Loop Current Eddy (LCE). Within the upper 200m of the water column, periods characterized by the downward energy propagation dominate. In the layer below 200m, near-inertial waves propagate upward and downward, and the wave trains cannot be traced to a single source of energy. This suggests near-inertial waves within the main part of the water column are of ‘global’ rather than of ‘local’ origin. For most near-inertial wave generation events through wind forcing, the downward energy propagation could not be traced for any extended period of time and no deeper than approximately 200-m depth. The rate of downward energy propagation in the upper pycnocline is on the order of 10-12 m/day. For the near-inertial currents, the first two Empirical Orthogonal Functions (EOF) contribute only 40% into the total current variability for the period of LCE presence and 52% for the period of benign current conditions. The mode shapes vary within a wide range that, most likely, reflects a random distribution of mode shapes that depend on the lateral geometry of the forcing, mixed layer depth, and stratification.

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On the Mean Flow in the Western Gulf of Mexico and a Reappraisal of Errors in Ship-Drift Data

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0260.1 ◽

2020 ◽

Vol 50 (7) ◽

pp. 1983-1988

Author(s):

Wilton Sturges

Keyword(s):

Gulf Of Mexico ◽

Surface Flow ◽

Return Flow ◽

Loop Current ◽

Mean Flow ◽

The West ◽

Near Surface ◽

Southern Half ◽

The Mean ◽

Layer Flow

AbstractShip-drift data in the Gulf of Mexico have led to a perplexing result, that the near-surface flow in the west has a north–south mean, of the east–west flow, ~5–10 cm s−1 into a closed basin. Ship-drift data have been used in the past hundred years under the assumption that they are reasonably accurate; the present study examines that assumption carefully, finding that the standard deviation of individual observations is typically ~20 cm s−1. In a monthly mean composed of order 400 observations or more, as examined here, the standard error of the mean will be reduced accordingly. In the southern part of the western Gulf of Mexico, the observed upper-layer flow is clearly to the west and is consistent with our expectations. In the northern part, however, the apparent flow as reported by ship drift in deep water is not significantly different from zero. Thus, the puzzling result remains: three different datasets in the southern half of the basin clearly show flow to the west, with speeds of 10 cm s−1 or more, yet there is no clear evidence of a near-surface return flow back to the east. The convergent wind stress forces downwelling of the upper layer; its return flow could be at some intermediate depth. The transport to the west from Loop Current rings is possibly returned in a deep boundary flow driven by the rectification of deep topographic Rossby waves.

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Is the Loop Current a Chaotic Oscillator?

Journal of Physical Oceanography ◽

10.1175/jpo3066.1 ◽

2007 ◽

Vol 37 (6) ◽

pp. 1455-1469 ◽

Cited By ~ 28

Author(s):

Alexis Lugo-Fernández

Keyword(s):

Dynamical Systems ◽

Gulf Of Mexico ◽

North Atlantic ◽

Chaotic Oscillator ◽

Loop Current ◽

The North ◽

Short Memory ◽

The North Atlantic ◽

Yucatan Channel ◽

The North Atlantic Oscillation

Abstract Dynamical systems theory is employed to study the irregular Loop Current in the Gulf of Mexico using a short database of shedding periods and north–south positions of the current. Two independent tests based on these data suggest that the Loop Current is not chaotic but behaves as a nonlinear driven and dampened oscillator with a very short memory. It is suggested that this current varies around a limit-cycle elliptical attractor. It was found that the amplitude and period of the oscillation vary at time scales of 3–5 yr, a time scale that agrees with those of the North Atlantic Oscillation (NAO) and/or ENSO; however, it is proposed that NAO provides the link between these systems. The proposed mechanism is the ITCZ changes caused by NAO, which affects the wind strength and the transport across the Yucatan Channel. A forecasting scheme that allows for prediction of the next eddy-shedding period from knowledge of the last shedding event, a condition caused by the short memory of the system, is provided.

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