Instabilities and Multiscale Interactions Underlying the Loop Current Eddy Shedding in the Gulf of Mexico

2020 ◽  
Vol 50 (5) ◽  
pp. 1289-1317
Author(s):  
Yang Yang ◽  
Robert H. Weisberg ◽  
Yonggang Liu ◽  
X. San Liang
Keyword(s):  
Energy Transfer ◽  
Gulf Of Mexico ◽  
High Frequency ◽  
Baroclinic Instability ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Loop Current ◽  
Background Flow ◽  
Pressure Work ◽  
Eddy Shedding

AbstractA recently developed tool, the multiscale window transform, along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities in the Gulf of Mexico Loop Current (LC) eddy shedding. A three-scale energetics framework is employed, in which the LC system is reconstructed onto a background flow window, a mesoscale eddy window, and a high-frequency eddy window. The canonical energy transfer between the background flow and the mesoscale windows plays an important role in LC eddy shedding. Barotropic instability contributes to the generation/intensification of the mesoscale eddies over the eastern continental slope of the Campeche Bank. Baroclinic instability favors the growth of the mesoscale eddies that propagate downstream to the northeastern portion of the well-extended LC, eventually causing the shedding by cutting through the neck of the LC. These upper-layer mesoscale eddies lose their kinetic energy back to the background LC through inverse cascade processes in the neck region. The deep eddies obtain energy primarily from the upper layer through vertical pressure work and secondarily from baroclinic instability in the deep layer. In contrast, the canonical energy transfer between the mesoscale and the high-frequency frontal eddy windows accounts for only a small fraction in the mesoscale eddy energy balance, and this generally acts as a damping mechanism for the mesoscale eddies. A budget analysis reveals that the mesoscale eddy energy gained through the instabilities is balanced by horizontal advection, pressure work, and dissipation.

scholarly journals Loop Current Growth and Eddy Shedding Using Models and Observations: Analyses of the July 2011 Eddy-Shedding Event*

2013 ◽  
Vol 43 (5) ◽  
pp. 1015-1027 ◽  
Author(s):  
F.-H. Xu ◽  
Y.-L. Chang ◽  
L.-Y. Oey ◽  
P. Hamilton
Keyword(s):  
Baroclinic Instability ◽  
Trade Wind ◽  
Loop Current ◽  
Reduced Gravity ◽  
Westward Expansion ◽  
Wave Dynamics ◽  
Orthogonal Function ◽  
Current Growth ◽  
The Caribbean ◽  
Eddy Shedding

Abstract Recent studies suggest that as the trade wind in the Caribbean Sea weakens from summer to fall, conditions become more favorable for the Loop Current in the Gulf of Mexico to shed an anticyclonic ring. This idea originated with observations showing a preference for more eddies from summer through fall, and it was confirmed using multidecadal model experiments. Here, the hypothesis is further tested by studying the dynamics of a specific eddy-shedding event in summer 2011 using a model experiment initialized with observation-assimilated reanalysis and forced by reanalysis wind from NCEP. Eddy shedding in July 2011 is shown to follow the weakening of the trade wind and Yucatan transport in late June. The shedding time is significantly earlier than can be explained based on reduced-gravity Rossby wave dynamics. Altimetry and model data are analyzed to show that empirical orthogonal function modes 1 + 2 dominate the reduced-gravity process, while higher modes contain the coupling of the Loop Current with deep layer underneath. The Loop’s westward expansion at incipient shedding induces a deep cyclonic gyre in the eastern Gulf, embedded within which are small cyclones caused by the baroclinic instability of the strongly sheared current north of the Campeche Bank. The associated deep upwelling and upper-layer divergence from these cyclonic circulations accelerate eddy shedding.

Predictability of the Loop Current Variation and Eddy Shedding Process in the Gulf of Mexico Using an Artificial Neural Network Approach

2015 ◽  
Vol 32 (5) ◽  
pp. 1098-1111 ◽  
Author(s):  
Xiangming Zeng ◽  
Yizhen Li ◽  
Ruoying He
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Gulf Of Mexico ◽  
Function Analysis ◽  
Optimal Number ◽  
Loop Current ◽  
Neural Network Approach ◽  
Current Variation ◽  
Artificial Neural ◽  
Eddy Shedding

AbstractA novel approach based on an artificial neural network was used to forecast sea surface height (SSH) in the Gulf of Mexico (GoM) in order to predict Loop Current variation and its eddy shedding process. The empirical orthogonal function analysis method was applied to decompose long-term satellite-observed SSH into spatial patterns (EOFs) and time-dependent principal components (PCs). The nonlinear autoregressive network was then developed to predict major PCs of the GoM SSH in the future. The prediction of SSH in the GoM was constructed by multiplying the EOFs and predicted PCs. Model sensitivity experiments were conducted to determine the optimal number of PCs. Validations against independent satellite observations indicate that the neural network–based model can reliably predict Loop Current variations and its eddy shedding process for a 4-week period. In some cases, an accurate forecast for 5–6 weeks is possible.

scholarly journals Adjoint sensitivity studies of loop current and eddy shedding in the Gulf of Mexico

2013 ◽  
Vol 118 (7) ◽  
pp. 3315-3335 ◽  
Author(s):  
Ganesh Gopalakrishnan ◽  
Bruce D. Cornuelle ◽  
Ibrahim Hoteit
Keyword(s):  
Gulf Of Mexico ◽  
Loop Current ◽  
Adjoint Sensitivity ◽  
Sensitivity Studies ◽  
Eddy Shedding

Spatial and Temporal Characteristics of the Submesoscale Energetics in the Gulf of Mexico

2020 ◽  
Author(s):  
Yang Yang ◽  
James C. McWilliams ◽  
X. San Liang ◽  
Hong Zhang ◽  
Robert H. Weisberg ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Baroclinic Instability ◽  
Background Flow ◽  
Ocean Energy ◽  
Deep Basin ◽  
Energy Cascades ◽  
Eastern Gulf Of Mexico ◽  
Energy Cycle ◽  
Mesoscale Processes

AbstractThe submesoscale energetics of the eastern Gulf of Mexico (GoM) are. diagnosed using outputs from a 1/48° MITgcm simulation. Employed is a recently-developed, localized multiscale energetics formalism with three temporal scale ranges (or scale windows), namely, a background flow window, a mesoscale window, and a submesoscale window. It is found that the energy cascades are highly inhomogeneous in space. Over the eastern continental slope of the Campeche Bank, the submesoscale eddies are generated via barotropic instability, with forward cascades of kinetic energy (KE) following a weak seasonal variation. In the deep basin of the eastern GoM, the submesoscale KE exhibits a seasonal cycle, peaking in winter, maintained via baroclinic instability, with forward available potential energy (APE) cascades in the mixed layer, followed by a strong buoyancy conversion. A spatially-coherent pool of inverse KE cascade is found to extract energy from the submesoscale KE reservoir in this region to replenish the background flow. The northern GoM features the strongest submesoscale signals with a similar seasonality as seen in the deep basin. The dominant source for the submesoscale KE during winter is from buoyancy conversion and also from the forward KE cascades from mesoscale processes. To maintain the balance, the excess submesoscale KE must be dissipated by smaller-scale processes via a forward cascade, implying a direct route to fine-scale dissipation. Our results highlight that the role of submesoscale turbulence in the ocean energy cycle is region- and time-dependent.

High Frequency Satellite Surveillance of Gulf of Mexico Loop Current Frontal Eddy cyclones

OCEANS 2009 ◽  
2009 ◽  
Author(s):  
Nan Walker ◽  
Robert Leben ◽  
Steven Anderson ◽  
Alaric Haag ◽  
Chet Pilley
Keyword(s):  
Gulf Of Mexico ◽  
High Frequency ◽  
Loop Current

scholarly journals Loop Current Frontal Eddies: Formation along the Campeche Bank and Impact of Coastally Trapped Waves

2016 ◽  
Vol 46 (11) ◽  
pp. 3339-3363 ◽  
Author(s):  
Julien Jouanno ◽  
José Ochoa ◽  
Enric Pallàs-Sanz ◽  
Julio Sheinbaum ◽  
Fernando Andrade-Canto ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
High Frequency ◽  
Process Model ◽  
Large Scale ◽  
Low Frequency ◽  
Loop Current ◽  
Trapped Waves ◽  
Cyclonic Vorticity ◽  
Wind Variability ◽  
Coastally Trapped Waves

AbstractVelocity data from a mooring array deployed northeast of the Campeche Bank (CB) show the presence of subinertial, high-frequency (below 15 days) velocity fluctuations within the core of the northward flowing Loop Current. These fluctuations are associated with the presence of surface-intensified Loop Current frontal eddies (LCFEs), with cyclonic vorticity and diameter < 100 km. These eddies are well reproduced by a high-resolution numerical simulation of the Gulf of Mexico, and the model analysis suggests that they originate along and north of the CB, their main energy source being the mixed baroclinic–barotropic instability of the northward flow along the shelf break. There is no indication that these high-frequency LCFEs contribute to the LC eddy detachment in contrast to the low-frequency LCFEs (periods > 30 days) that have been linked to Caribbean eddies and the LC separation process. Model results show that wind variability associated with winter cold surges are responsible for the emergence of high-frequency LCFEs in a narrow band of periods (6–10 day) in the region of the CB. The dynamical link between the formation of these LCFEs and the wind variability is not direct: (i) the large-scale wind perturbations generate sea level anomalies on the CB as well as first baroclinic mode, coastally trapped waves in the western Gulf of Mexico; (ii) these waves propagate cyclonically along the coast; and (iii) the interaction of these anomalies with the Loop Current triggers cyclonic vorticity perturbations that grow in intensity as they propagate downstream and develop into cyclonic eddies when they flow north of the Yucatan shelf.

Observed Energy Exchange between Low-Frequency Flows and Internal Waves in the Gulf of Mexico

2018 ◽  
Vol 48 (4) ◽  
pp. 995-1008 ◽  
Author(s):  
Zhao Jing ◽  
Ping Chang ◽  
S. F. DiMarco ◽  
Lixin Wu
Keyword(s):  
Energy Transfer ◽  
Gulf Of Mexico ◽  
Internal Waves ◽  
High Frequency ◽  
Energy Exchange ◽  
Low Frequency ◽  
Net Energy ◽  
Energy Transfer Rate ◽  
Capture Mechanism

AbstractA long-term mooring array deployed in the northern Gulf of Mexico is used to analyze energy exchange between internal waves and low-frequency flows. In the subthermocline (245–450 m), there is a noticeable net energy transfer from low-frequency flows, defined as having a period longer than six inertial periods, to internal waves. The magnitude of energy transfer rate depends on the Okubo–Weiss parameter of low-frequency flows. A permanent energy exchange occurs only when the Okubo–Weiss parameter is positive. The near-inertial internal waves (NIWs) make major contribution to the energy exchange owing to their energetic wave stress and relatively stronger interaction with low-frequency flows compared to the high-frequency internal waves. There is some evidence that the permanent energy exchange between low-frequency flows and NIWs is attributed to the partial realization of the wave capture mechanism. In the periods favoring the occurrence of the wave capture mechanism, the horizontal propagation direction of NIWs becomes anisotropic and exhibits evident tendency toward that predicted from the wave capture mechanism, leading to pronounced energy transfer from low-frequency flows to NIWs.

The influence of Gulf of Mexico Loop Current intrusion on the transport of the Florida Current

2010 ◽  
Vol 60 (5) ◽  
pp. 1075-1084 ◽  
Author(s):  
Yuehua Lin ◽  
Richard J. Greatbatch ◽  
Jinyu Sheng
Keyword(s):  
Gulf Of Mexico ◽  
Florida Current ◽  
Loop Current

Development of a Stepped Line Tensioning Solution for Mitigating VIM Effects in Loop Eddy Currents for the Genesis Spar

2004 ◽  
Author(s):  
T. Kokkinis ◽  
R. E. Sandstro¨m ◽  
H. T. Jones ◽  
H. M. Thompson ◽  
W. L. Greiner
Keyword(s):  
Gulf Of Mexico ◽  
Eddy Current ◽  
Eddy Currents ◽  
Comprehensive Evaluation ◽  
Design Solution ◽  
Loop Current ◽  
Mooring Lines ◽  
Test Methodology ◽  
Induced Motion ◽  
High Reynolds

A number of spars are being installed in deepwater areas in the Gulf of Mexico (GoM), which are subject to loop / eddy current conditions and must be designed for Vortex-Induced Motion (VIM). This paper shows how recent advances in VIM prediction enabled an efficient and effective mooring design solution for the existing Genesis classic spar, which is installed in Green Canyon Block 205 in the GOM. The solution may also be applicable to new spar designs. During the Gulf of Mexico Millennium Eddy Current event in April 2001, the Genesis spar platform underwent vortex induced motions (VIM) which were greater than anticipated during the design of the mooring & riser systems. Analysis showed that if such large motions were to occur in higher currents in the range of the 100-year event, they could cause significant fatigue damage, and could lead to peak tensions in excess of design allowables. After a comprehensive evaluation of potential solutions, Stepped Line Tensioning (SLT) was determined to be the best approach for restoring the platform’s original mooring capacity on technical, cost and schedule grounds. SLT did not require extensive redesign of the existing mooring system of the spar. Furthermore, SLT provided a means to improve mooring integrity on an interim basis, while completing details for permanent implementation. Under SLT, the pretensions of the mooring lines are adjusted based on forecast currents in order to keep the platform below the VIM lock-in threshold at all times and for all eddy/loop current conditions up to and including the 100-year condition. High Reynolds number model tests conducted with a new test methodology were used to get a reliable prediction of the spar’s VIM response for this evaluation.

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