scholarly journals Near-Surface and Deep Circulation Coupling in the Western Gulf of Mexico

2018 ◽  
Vol 48 (1) ◽  
pp. 145-161 ◽  
Author(s):  
M. Tenreiro ◽  
Julio Candela ◽  
Enric Pallàs Sanz ◽  
Julio Sheinbaum ◽  
José Ochoa
Keyword(s):  
Gulf Of Mexico ◽  
Surface Currents ◽  
Loop Current ◽  
Cyclonic Gyre ◽  
Cyclonic Vorticity ◽  
Near Surface ◽  
Deep Circulation ◽  
Rear Part ◽  
The Mean ◽  
Mean Circulation

AbstractThe coupling between the upper (z < 1000-m depth) and deep (z > 1500 m) circulation in the western Gulf of Mexico (WGoM) driven by the arrival of Loop Current eddies (LCEs) is analyzed from moorings measuring horizontal velocity in the full water column during a 5-yr period (October 2008–October 2013). Nine LCEs crossing the mooring array are documented. A composite of these events shows that strong northward currents at depth having speeds of 0.1–0.2 m s−1 precede (~10–20 days) the strong northward near-surface currents (~0.5 m s−1) characteristic of the western rim of the LCEs. These deep northward flow intensifications are followed by southward deep flows coupled with the surface-intensified southward current of the eastern (rear) part of the LCEs crossing the array. These results are consistent with the existence of a deep anticyclone leading and a cyclone trailing the upper-layer LCEs. Objectively interpolated regional maps of velocities and vertical vorticity obtained from up to 30 moorings indicate the mean circulation at 100-m depth in the northern WGoM is mostly anticyclonic and enhanced by the arrival of the westward-propagating LCEs, while the southern part is dominated by the presence of a semipermanent cyclonic structure (Bay of Campeche cyclonic gyre). At 1500-m depth, the mean circulation follows the slope in a cyclonic sense and shows a cyclonic vorticity maximum on the abyssal plane consistent with the LCE deep flow composites. This suggests the LCEs strongly modulate not only the upper-layer circulation but also impact the deep flow.

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

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.

scholarly journals Assessment of Numerical Simulations of Deep Circulation and Variability in the Gulf of Mexico Using Recent Observations

2020 ◽  
Vol 50 (4) ◽  
pp. 1045-1064 ◽  
Author(s):  
Steven L. Morey ◽  
Ganesh Gopalakrishnan ◽  
Enric Pallás Sanz ◽  
Joao Marcos Azevedo Correia De Souza ◽  
Kathleen Donohue ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Numerical Simulations ◽  
General Circulation ◽  
Large Scale ◽  
General Circulation Models ◽  
Striking Difference ◽  
Loop Current ◽  
Deep Circulation ◽  
Velocity Statistics ◽  
Current Region

AbstractThree simulations of the circulation in the Gulf of Mexico (the “Gulf”) using different numerical general circulation models are compared with results of recent large-scale observational campaigns conducted throughout the deep (>1500 m) Gulf. Analyses of these observations have provided new understanding of large-scale mean circulation features and variability throughout the deep Gulf. Important features include cyclonic flow along the continental slope, deep cyclonic circulation in the western Gulf, a counterrotating pair of cells under the Loop Current region, and a cyclonic cell to the south of this pair. These dominant circulation features are represented in each of the ocean model simulations, although with some obvious differences. A striking difference between all the models and the observations is that the simulated deep eddy kinetic energy under the Loop Current region is generally less than one-half of that computed from observations. A multidecadal integration of one of these numerical simulations is used to evaluate the uncertainty of estimates of velocity statistics in the deep Gulf computed from limited-length (4 years) observational or model records. This analysis shows that the main deep circulation features identified from the observational studies appear to be robust and are not substantially impacted by variability on time scales longer than the observational records. Differences in strengths and structures of the circulation features are identified, however, and quantified through standard error analysis of the statistical estimates using the model solutions.

scholarly journals Loop Current rings and the deep circulation in the Gulf of Mexico

2000 ◽  
Vol 105 (C7) ◽  
pp. 16951-16959 ◽  
Author(s):  
Susan Elizabeth Welsh ◽  
Masamichi Inoue
Keyword(s):  
Gulf Of Mexico ◽  
Loop Current ◽  
Deep Circulation

scholarly journals Observations and a Model of the Mean Circulation over the Middle Atlantic Bight Continental Shelf

2008 ◽  
Vol 38 (6) ◽  
pp. 1203-1221 ◽  
Author(s):  
Steven J. Lentz
Keyword(s):  
Pressure Gradient ◽  
Continental Shelf ◽  
Shallow Water ◽  
Water Depth ◽  
Circulation Pattern ◽  
Near Surface ◽  
Middle Atlantic ◽  
The Mean ◽  
Offshore Flow ◽  
Mean Circulation

Abstract Analyses of current time series longer than 200 days from 33 sites over the Middle Atlantic Bight continental shelf reveal a consistent mean circulation pattern. The mean depth-averaged flow is equatorward, alongshelf, and increases with increasing water depth from 3 cm s−1 at the 15-m isobath to 10 cm s−1 at the 100-m isobath. The mean cross-shelf circulation exhibits a consistent cross-shelf and vertical structure. The near-surface flow is typically offshore (positive, range −3 to 6 cm s−1). The interior flow is onshore and remarkably constant (−0.2 to −1.4 cm s−1). The near-bottom flow increases linearly with increasing water depth from −1 cm s−1 (onshore) in shallow water to 4 cm s−1 (offshore) at the 250-m isobath over the slope, with the direction reversal near the 50-m isobath. A steady, two-dimensional model (no along-isobath variations in the flow) reproduces the main features of the observed circulation pattern. The depth-averaged alongshelf flow is primarily driven by an alongshelf pressure gradient (sea surface slope of 3.7 × 10−8 increasing to the north) and an opposing mean wind stress that also drives the near-surface offshore flow. The alongshelf pressure gradient accounts for both the increase in the alongshelf flow with water depth and the geostrophic balance onshore flow in the interior. The increase in the near-bottom offshore flow with water depth is due to the change in the relative magnitude of the contributions from the geostrophic onshore flow that dominates in shallow water and the offshore flow driven by the bottom stress that dominates in deeper water.

scholarly journals A gridded surface current product for the Gulf of Mexico from consolidated drifter measurements

2021 ◽  
Vol 13 (2) ◽  
pp. 645-669
Author(s):  
Jonathan M. Lilly ◽  
Paula Pérez-Brunius
Keyword(s):  
Gulf Of Mexico ◽  
Temporal Distribution ◽  
Surface Current ◽  
Large Set ◽  
Surface Currents ◽  
Important Region ◽  
Surface Drifter ◽  
Current Product ◽  
The Mean ◽  
Separate Product

Abstract. A large set of historical surface drifter data from the Gulf of Mexico – 3770 trajectories spanning 28 years and more than a dozen data sources – are collected, uniformly processed and quality controlled, and assimilated into a spatially and temporally gridded dataset called GulfFlow. This dataset is available in two versions, with 1/4∘ or 1/12∘ spatial resolution respectively, both of which have overlapping monthly temporal bins with semimonthly spacing and which extend from the years 1992 through 2020. Together these form a significant resource for studying the circulation and variability in this important region. The uniformly processed historical drifter data from all publicly available sources, interpolated to hourly resolution, are also distributed in a separate product called GulfDriftersOpen. Forming a mean surface current map by directly bin-averaging the hourly drifter data is found to lead to severe artifacts, a consequence of the extremely inhomogeneous temporal distribution of the drifters. Averaging instead the already monthly-averaged data in GulfFlow avoids these problems, resulting in the highest-resolution map of the mean Gulf of Mexico surface currents yet produced. The consolidated drifter dataset is freely available at https://doi.org/10.5281/zenodo.3985916 (Lilly and Pérez-Brunius, 2021a), while the gridded products are available for noncommercial use only (for reasons discussed herein) at https://doi.org/10.5281/zenodo.3978793 (Lilly and Pérez-Brunius, 2021b).

scholarly journals Subsurface Jets in the Northwestern Gulf of Mexico

2009 ◽  
Vol 39 (11) ◽  
pp. 2875-2891 ◽  
Author(s):  
Peter Hamilton ◽  
Antoine Badan
Keyword(s):  
Velocity Profile ◽  
Gulf Of Mexico ◽  
Internal Waves ◽  
Vertical Axis ◽  
Surface Currents ◽  
Profile Data ◽  
Near Surface ◽  
Anomalous Density ◽  
Slope Topography ◽  
Upper Slope

Abstract Subsurface jets, defined as having velocity maxima &gt;40 cm s−1 at depths between 100 and 350 m, and being surrounded by much weaker near-surface currents, have been observed over the northwestern Gulf of Mexico continental slope. The observations were from an array of 14 moorings equipped with upward-looking 75-kHz ADCPs deployed at 450–500 m. A total of 10 jet events were observed in 18 ADCP years of velocity profile data, where these events were clearly not the result of downward-propagating inertial internal waves. The jets had durations from about 1 to 8 days and were usually associated with interactions between similarly sized cyclones and anticyclones over the slope or with the interaction of an eddy with upper-slope topography. The jets are associated with potential vorticity anomalies and their inferred length scales indicate that the dynamics depart from simple geostrophic balances. Observed anomalous density gradients present during the jets seem to involve the tilting of the vertical axis of the center of rotation of one or more of the interacting eddies.

The Mean Meridional Circulation of the Atmosphere Using the Mass above Isentropes as the Vertical Coordinate

2013 ◽  
Vol 70 (7) ◽  
pp. 2197-2213 ◽  
Author(s):  
Gang Chen
Keyword(s):  
Small Amplitude ◽  
Meridional Circulation ◽  
Surface Flow ◽  
Department Of Energy ◽  
Flux Divergence ◽  
Near Surface ◽  
Vertical Coordinate ◽  
Mean Meridional Circulation ◽  
The Mean ◽  
Mean Circulation

Abstract The mean meridional circulation of the atmosphere is presented using the mass (more specifically, the pressure corresponding to the mass) above the isentrope of interest as the vertical coordinate. In this vertical coordinate, the mass-weighted mean circulation is exactly balanced by entropy sources and sinks with no eddy flux contribution as in the isentropic coordinate, and the coordinate can be readily generalized to the mass above moist isentropes or other quasi-conservative tracers by construction. The corresponding Eliassen–Palm (EP) flux divergence for the zonal-mean angular momentum is formulated in a hybrid isobaric–isentropic form, extending the conventional transformed Eulerian-mean (TEM) formulation to finite-amplitude nongeostrophic eddies on the sphere. In the small-amplitude limit, the hybrid isobaric–isentropic formulation reduces to the TEM formulation. Applying to the NCEP–U.S. Department of Energy (DOE) Reanalysis 2, the new formulation resolves the deficiency of the conventional TEM formulation for the near-surface flow, where the isentropic surface intersects the ground, and the mean circulation agrees well with the TEM above the near-surface layer. In the small-amplitude limit, this improvement near the surface can be partially attributed to the isentropic static stability over the isobaric counterpart, as the mass density in the near-surface isentropic layers gradually approaches zero. Also, the mean mass streamfunction can be approximately obtained from the EP flux divergence except for the deep tropics or the near-surface flow, highlighting the dominant control of potential vorticity mixing for the subtropics-to-pole mean circulations. It is then expected to provide a valuable diagnostic framework not only for global circulation theory, but also for atmospheric transport in the troposphere.

scholarly journals Dominant Circulation Patterns of the Deep Gulf of Mexico

2018 ◽  
Vol 48 (3) ◽  
pp. 511-529 ◽  
Author(s):  
Paula Pérez-Brunius ◽  
Heather Furey ◽  
Amy Bower ◽  
Peter Hamilton ◽  
Julio Candela ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Large Scale ◽  
Bottom Layer ◽  
Loop Current ◽  
Cyclonic Gyre ◽  
Boundary Current ◽  
Mean Flow ◽  
Western Basin ◽  
Boundary Flow ◽  
Circulation Patterns

AbstractThe large-scale circulation of the bottom layer of the Gulf of Mexico is analyzed, with special attention to the historically least studied western basin. The analysis is based on 4 years of data collected by 158 subsurface floats parked at 1500 and 2500 m and is complemented with data collected by current meter moorings in the western basin during the same period. Three main circulation patterns stand out: a cyclonic boundary current, a cyclonic gyre in the abyssal plain, and the very high eddy kinetic energy observed in the eastern Gulf. The boundary current and the cyclonic gyre appear as distinct features, which interact in the western tip of the Yucatan shelf. The persistence and continuity of the boundary current is addressed. Although high variability is observed, the boundary flow serves as a pathway for water to travel around the western basin in approximately 2 years. An interesting discovery is the separation of the boundary current over the northwestern slope of the Yucatan shelf. The separation and retroflection of the along-slope current appears to be a persistent feature and is associated with anticyclonic eddies whose genesis mechanism remains to be understood. As the boundary flow separates, it feeds into the westward flow of the deep cyclonic gyre. The location of this gyre—named the Sigsbee Abyssal Gyre—coincides with closed geostrophic contours, so eddy–topography interaction via bottom form stresses may drive this mean flow. The contribution to the cyclonic vorticity of the gyre by modons traveling under Loop Current eddies is discussed.

scholarly journals Comments on Southern Ocean Near-Surface Circulation and its Variability

1980 ◽  
Vol 1 ◽  
pp. 57-60 ◽  
Author(s):  
Arnold L. Gordon
Keyword(s):  
Surface Layer ◽  
Literature Review ◽  
Southern Ocean ◽  
Near Surface ◽  
Surface Circulation ◽  
Variable Surface ◽  
The Mean ◽  
Mean Circulation

This literature review discusses the mean and variable surface-layer circulation of the Southern Ocean. The variable components are equal to or even more energetic than the mean circulation. Therefore circulation charts often do not present the significant currents that exist during specific periods.

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.

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