scholarly journals Observations of Layering under a Warm-Core Ring in the Gulf of Mexico

2019 ◽  
Vol 49 (12) ◽  
pp. 3145-3162 ◽  
Author(s):  
Thomas Meunier ◽  
Enric Pallàs Sanz ◽  
Miguel Tenreiro ◽  
José Ochoa ◽  
Angel Ruiz Angulo ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Initial Conditions ◽  
Thin Layers ◽  
Vertical Shear ◽  
Observation Data ◽  
Loop Current ◽  
Warm Core ◽  
Vertical Scale ◽  
Differential Advection ◽  
Vertical Scales

AbstractTwo glider transects in the Gulf of Mexico reveal fine-vertical-scale thermohaline structures within a Loop Current eddy (LCE). Partially compensating temperature and salinity anomalies are shown to organize as thin layers below the eddy and near its edges. The anomalies have vertical scales ranging from 2 to 60 m and extend laterally over distances up to 120 km. These structures are evident in synthetic acoustic reflectivity derived from the glider data and are reminiscent of the intense layering observed in seismic imagery around meddies, Agulhas rings, and warm-core Kuroshio rings. The observed layers are aligned with the geostrophic streamfunction rather than isopycnals and develop preferentially in zones of intense vertical shear. These observations suggest that tracer stirring by the eddy’s vertically sheared azimuthal flow might be an important process for their generation. In an attempt to rationalize this process, high-resolution quasigeostrophic simulations were performed using an idealized anticyclonic ring for the initial conditions. As the vortex destabilizes, layering rapidly develops in the model, resulting in structures similar to those found in the observation data. Passive tracer experiments also suggest that the layers form through differential advection of the tracer field by the vertically sheared flow associated with the LCE.

scholarly journals The Surface Circulation of the Caribbean Sea and the Gulf of Mexico as Inferred from Satellite Altimetry

2009 ◽  
Vol 39 (3) ◽  
pp. 640-657 ◽  
Author(s):  
Aida Alvera-Azcárate ◽  
Alexander Barth ◽  
Robert H. Weisberg
Keyword(s):  
Gulf Of Mexico ◽  
Time Scales ◽  
Satellite Altimetry ◽  
Southern Oscillation ◽  
Caribbean Sea ◽  
Vertical Shear ◽  
Loop Current ◽  
Surface Circulation ◽  
The Caribbean ◽  
Anticyclonic Eddies

Abstract The surface circulation of the Caribbean Sea and Gulf of Mexico is studied using 13 years of satellite altimetry data. Variability in the Caribbean Sea is evident over several time scales. At the annual scale, sea surface height (SSH) varies mainly by a seasonal steric effect. Interannually, a longer cycle affects the SSH slope across the current and hence the intensity of the Caribbean Current. This cycle is found to be related to changes in the wind intensity, the wind stress curl, and El Niño–Southern Oscillation. At shorter time scales, eddies and meanders are observed in the Caribbean Current, and their propagation speed is explained by baroclinic instabilities under the combined effect of vertical shear and the β effect. Then the Loop Current (LC) is considered, focusing on the anticyclonic eddies shed by it and the intrusion of the LC into the Gulf of Mexico through time. Twelve of the 21 anticyclonic eddies observed to detach from the LC are shed from July to September, suggesting a seasonality in the timing of these events. Also, a relation is found between the intrusion of the LC into the Gulf of Mexico and the size of the eddies shed from it: larger intrusions trigger smaller eddies. A series of extreme LC intrusions into the Gulf of Mexico, when the LC is observed as far as 92°W, are described. The analyses herein suggest that the frequency of such events has increased in recent years, with only one event occurring in 1993 versus three from 2002 to 2006. Transport through the Straits of Florida appears to decrease during these extreme intrusions.

Turbulence Measurements in a Gulf of Mexico Warm-Core Ring

2007 ◽  
Author(s):  
Thomas M. Mitchell ◽  
Rolf G. Lueck ◽  
Michael J. Vogel ◽  
Robert E. Raye ◽  
George Z. Forristall
Keyword(s):  
Gulf Of Mexico ◽  
Gulf Stream ◽  
Noise Level ◽  
Acoustic Doppler Current Profiler ◽  
Florida Current ◽  
Depth Range ◽  
Loop Current ◽  
Environmental Signals ◽  
Warm Core ◽  
Warm Core Ring

Oceanographic measurements were made in a Loop Current Eddy in the Gulf of Mexico to characterize the turbulence associated with these eddies. Measurements were made within the eddy, and across the strong frontal boundary delineating the eddy from the surrounding waters. The survey was conducted August 23–30, 2003, from the R/V Pelican. The towed vehicle, the TOMI, was equipped with a special 300 kHz acoustic Doppler current profiler (Medusa ADCP) that had its four beams directed fore, port, starboard and down. The along-beam velocities resolved structures with wavelengths of 4 to 60 m. The vehicle also carried shear probes for measuring velocity fluctuations in the dissipation range (0.5 to 100 cycles per meter), and other environmental sensors for measuring temperature, salinity, depth and vehicle orientation. Ship equipment included a 75 and 300 kHz hull-mounted ADCP, CTD, and meteorological sensors. Tows were conducted at 25, 50, 100 and 150 m depths around the northern edge of the Loop Eddy in currents of up to 1.7 m s−1. Turbulence was detected with the shear probes, but mostly in the 130–150 m depth range around the local salinity maxima. The level of turbulence is weak and it is distributed intermittently in both space and time. The most energetic events of turbulence have eddy scales of at most 4 meters and velocity scales of only 1 cm s−1. The typical and average values are more than 10 times smaller. The concurrent measurements of velocity with the Medusa ADCP did not reveal any signals significantly larger than the noise level of this instrumentation, namely 2 cm s−1. Overlap averaging of the forward directed beam reduced the noise level to 0.5 cm s−1 but still failed to reveal real environmental signals. This “null-result” is consistent with the simultaneous measurements taken with the shear probe. These low levels of turbulence are also consistent with reports of measurements in the Gulf Stream, the Florida Current, and a Gulf Stream Warm-Core Ring. Funding was provided by the DeepStar oil industry research consortium. Complete details of the program are provided in Reference [6].

scholarly journals The Dynamical Structure of a Warm Core Ring as Inferred from Glider Observations and Along-Track Altimetry

2021 ◽  
Vol 13 (13) ◽  
pp. 2456
Author(s):  
Thomas Meunier ◽  
Enric Pallás Sanz ◽  
Charly de Marez ◽  
Juan Pérez ◽  
Miguel Tenreiro ◽  
...  
Keyword(s):  
Rotation Axis ◽  
Relative Vorticity ◽  
Dynamical Structure ◽  
Loop Current ◽  
Energy Partition ◽  
Warm Core ◽  
Warm Core Ring ◽  
Current Ring ◽  
Along Track ◽  
Pv Gradient

This study investigates the vertical structure of the dynamical properties of a warm-core ring in the Gulf of Mexico (Loop Current ring) using glider observations. We introduce a new method to correct the glider’s along-track coordinate, which is, in general, biased by the unsteady relative movements of the glider and the eddy, yielding large errors on horizontal derivatives. Here, we take advantage of the synopticity of satellite along-track altimetry to apply corrections on the glider’s position by matching in situ steric height with satellite-measured sea surface height. This relocation method allows recovering the eddy’s azimuthal symmetry, precisely estimating the rotation axis position, and computing reliable horizontal derivatives. It is shown to be particularly appropriate to compute the eddy’s cyclo-geostrophic velocity, relative vorticity, and shear strain, which are otherwise out of reach when using the glider’s raw traveled distance as a horizontal coordinate. The Ertel potential vorticity (PV) structure of the warm core ring is studied in details, and we show that the PV anomaly is entirely controlled by vortex stretching. Sign reversal of the PV gradient across the water column suggests that the ring might be baroclinically unstable. The PV gradient is also largely controlled by gradients of the vortex stretching term. We also show that the ring’s total energy partition is strongly skewed, with available potential energy being 3 times larger than kinetic energy. The possible impact of this energy partition on the Loop Current rings longevity is also discussed.

scholarly journals Simulations of Switchback, Fragmentation and Sunspot Pair in δ-Sunspots during Magnetic Flux Emergence

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 586
Author(s):  
Che-Jui Chang ◽  
Jean-Fu Kiang
Keyword(s):  
Magnetic Field ◽  
Solar System ◽  
Field Strength ◽  
Magnetic Flux ◽  
Initial Conditions ◽  
Observation Data ◽  
Flux Emergence ◽  
Polarity Inversion ◽  
Simulation Results ◽  
Spot Type

Strong flares and coronal mass ejections (CMEs), launched from δ-sunspots, are the most catastrophic energy-releasing events in the solar system. The formations of δ-sunspots and relevant polarity inversion lines (PILs) are crucial for the understanding of flare eruptions and CMEs. In this work, the kink-stable, spot-spot-type δ-sunspots induced by flux emergence are simulated, under different subphotospheric initial conditions of magnetic field strength, radius, twist, and depth. The time evolution of various plasma variables of the δ-sunspots are simulated and compared with the observation data, including magnetic bipolar structures, relevant PILs, and temperature. The simulation results show that magnetic polarities display switchbacks at a certain stage and then split into numerous fragments. The simulated fragmentation phenomenon in some δ-sunspots may provide leads for future observations in the field.

scholarly journals Recent Advances in Our Understanding of Tropical Cyclone Intensity Change Processes from Airborne Observations

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 650
Author(s):  
Robert F. Rogers
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Vertical Shear ◽  
Intensity Change ◽  
Change Processes ◽  
Cyclone Intensity ◽  
Secondary Eyewall Formation ◽  
Warm Core ◽  
Major Hurricane ◽  
Upper Level

Recent (past ~15 years) advances in our understanding of tropical cyclone (TC) intensity change processes using aircraft data are summarized here. The focus covers a variety of spatiotemporal scales, regions of the TC inner core, and stages of the TC lifecycle, from preformation to major hurricane status. Topics covered include (1) characterizing TC structure and its relationship to intensity change; (2) TC intensification in vertical shear; (3) planetary boundary layer (PBL) processes and air–sea interaction; (4) upper-level warm core structure and evolution; (5) genesis and development of weak TCs; and (6) secondary eyewall formation/eyewall replacement cycles (SEF/ERC). Gaps in our airborne observational capabilities are discussed, as are new observing technologies to address these gaps and future directions for airborne TC intensity change research.

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.

scholarly journals A Lagrangian approach to the Loop Current eddy separation

2013 ◽  
Vol 20 (1) ◽  
pp. 85-96 ◽  
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.

scholarly journals Influence of frontal cyclone evolution on the 2009 (Ekman) and 2010 (Franklin) Loop Current eddy detachment events

Ocean Science ◽  
2014 ◽  
Vol 10 (6) ◽  
pp. 947-965 ◽  
Author(s):  
Y. S. Androulidakis ◽  
V. H. Kourafalou ◽  
M. Le Hénaff
Keyword(s):  
Numerical Simulation ◽  
Gulf Of Mexico ◽  
Satellite Data ◽  
Potential Vorticity ◽  
In Situ Measurements ◽  
Loop Current ◽  
Positive Potential ◽  
Eastern Gulf Of Mexico ◽  
And Migration

Abstract. The anticyclonic Loop Current Eddy (LCE) shedding events are strongly associated with the evolution of Loop Current Frontal Eddies (LCFEs) over the eastern Gulf of Mexico (GoM). A numerical simulation, in tandem with in situ measurements and satellite data, was used to investigate the Loop Current (LC) evolution and the surrounding LCFE formation, structure, growth and migration during the Eddy Ekman and Eddy Franklin shedding events in the summers of 2009 and 2010, respectively. During both events, northern GoM LCFEs appeared vertically coherent to at least 1500 m in temperature observations. They propagated towards the base of the LC, where, together with the migration of Campeche Bank (southwest GoM shelf) eddies from south of the LC, contributed to its "necking-down". Growth of Campeche Bank LCFEs involved in Eddy Franklin was partially attributed to Campeche Bank waters following upwelling events. Slope processes associated with such upwelling included offshore exports of high positive potential vorticity that may trigger cyclone formation and growth. The advection and growth of LCFEs, originating from the northern and southern GoM, and their interaction with the LC over the LCE detachment area favor shedding conditions and may contribute to the final separation of the LCE.

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