scholarly journals Mesoscale eddy formation and evolution in the ice-covered ocean

1991 ◽  
Vol 15 ◽  
pp. 139-147 ◽  
Author(s):  
Motoyoshi Ikeda
Keyword(s):  
Deep Convection ◽  
Bottom Topography ◽  
Active Material ◽  
Mesoscale Eddy ◽  
Open Water ◽  
Ekman Pumping ◽  
Strong Current ◽  
Eddy Formation ◽  
Current Instability ◽  
Generation Mechanisms

Generation mechanisms of mesoscale eddies in the ice-covered ocean are studied by using numerical ice–ocean models and discussed with reference to previous papers. The three possible mechanisms of eddy generation, with sea ice as a passive tracer, are current instability, current-eddy interaction and current–bottom topography interaction. The current instability, categorized into barotropic and baroclinic instabilities, may be responsible for eddies near the ice edge associated with a strong current. An eddy can interact with a current, producing additional eddies, where stability of the current is again an important factor for eddy formation. Eddies over bottom topography on the continental shelf are explained by current–topography interaction; i.e. anticyclones are produced over banks. The particular mechanism that includes ice as an active material is an ice–ocean interaction; i.e. a wind stress is larger over the ice than on open water and induces Ekman pumping and suction, which produce dipole eddy motions in the non-uniformly ice-covered ocean. The eddies are suggested to be important for cross-shelf exchanges of ice and heat as well as determining locations of deep convection.

scholarly journals Mesoscale eddy formation and evolution in the ice-covered ocean

1991 ◽  
Vol 15 ◽  
pp. 139-147
Author(s):  
Motoyoshi Ikeda
Keyword(s):  
Deep Convection ◽  
Bottom Topography ◽  
Active Material ◽  
Mesoscale Eddy ◽  
Open Water ◽  
Ekman Pumping ◽  
Strong Current ◽  
Eddy Formation ◽  
Current Instability ◽  
Generation Mechanisms

Generation mechanisms of mesoscale eddies in the ice-covered ocean are studied by using numerical ice–ocean models and discussed with reference to previous papers. The three possible mechanisms of eddy generation, with sea ice as a passive tracer, are current instability, current-eddy interaction and current–bottom topography interaction. The current instability, categorized into barotropic and baroclinic instabilities, may be responsible for eddies near the ice edge associated with a strong current. An eddy can interact with a current, producing additional eddies, where stability of the current is again an important factor for eddy formation. Eddies over bottom topography on the continental shelf are explained by current–topography interaction; i.e. anticyclones are produced over banks. The particular mechanism that includes ice as an active material is an ice–ocean interaction; i.e. a wind stress is larger over the ice than on open water and induces Ekman pumping and suction, which produce dipole eddy motions in the non-uniformly ice-covered ocean. The eddies are suggested to be important for cross-shelf exchanges of ice and heat as well as determining locations of deep convection.

scholarly journals The Behavior of Jet Currents over a Continental Slope Topography with a Possible Application to the Northern Current

2005 ◽  
Vol 35 (5) ◽  
pp. 790-810 ◽  
Author(s):  
M. M. Flexas ◽  
G. J. F. van Heijst ◽  
R. R. Trieling
Keyword(s):  
High Speed ◽  
Bottom Topography ◽  
Laboratory Model ◽  
Topographic Effects ◽  
Topographic Slope ◽  
Eddy Formation ◽  
Slow Flows ◽  
Bottom Depth ◽  
Source Sink ◽  
Northern Current

Abstract The Northern Current is a slope current in the northwest Mediterranean that shows high mesoscale variability, generally associated with meander and eddy formation. A barotropic laboratory model of this current is used here to study the role of the bottom topography on the current variability. For this purpose, a source–sink setup in a cylindrical tank placed on a rotating table is used to generate an axisymmetric barotropic current. To study inviscid topographic effects, experiments are performed over a topographic slope and also over a constant-depth setup, the latter being used as a reference for the former. With the aim of obtaining a fully comprehensive view of the vorticity balance at play, the flow may be forced in either azimuthal direction, leading to a “westward” prograde current (similar to the Northern Current) or an “eastward” retrograde current. For slow flows, eastward and westward currents showed similar patterns, dominated by Kelvin–Helmholtz-type instabilities. For high-speed flows, eastward and westward currents showed very different behavior. In eastward currents, the variability is observed to concentrate toward the center of the jet and shows strong meandering formation. Westward currents, instead, showed major variability toward the edges of the jet, together with a strong variability over the uppermost slope, which has been associated here with a topographic Rossby wave trapped over the shelf break. The differences between eastward and westward jets are explained through the balance between shear-induced and topographically induced vorticity at play in each case. Moreover, a model of jets over a beta plane is successfully applied here, allowing its extension to any ambient potential vorticity gradient caused either by latitudinal or bottom depth changes.

scholarly journals A Theory of the Wind-Driven Beaufort Gyre Variability

2016 ◽  
Vol 46 (11) ◽  
pp. 3263-3278 ◽  
Author(s):  
Georgy E. Manucharyan ◽  
Michael A. Spall ◽  
Andrew F. Thompson
Keyword(s):  
Time Scales ◽  
Large Scale ◽  
Climate Models ◽  
Numerical Models ◽  
Mesoscale Eddy ◽  
Eddy Diffusivity ◽  
The Arctic ◽  
Equilibration Time ◽  
Ekman Pumping ◽  
Beaufort Gyre

AbstractThe halocline of the Beaufort Gyre varies significantly on interannual to decadal time scales, affecting the freshwater content (FWC) of the Arctic Ocean. This study explores the role of eddies in the Ekman-driven gyre variability. Following the transformed Eulerian-mean paradigm, the authors develop a theory that links the FWC variability to the stability of the large-scale gyre, defined as the inverse of its equilibration time. The theory, verified with eddy-resolving numerical simulations, demonstrates that the gyre stability is explicitly controlled by the mesoscale eddy diffusivity. An accurate representation of the halocline dynamics requires the eddy diffusivity of 300 ± 200 m2 s−1, which is lower than what is used in most low-resolution climate models. In particular, on interannual and longer time scales the eddy fluxes and the Ekman pumping provide equally important contributions to the FWC variability. However, only large-scale Ekman pumping patterns can significantly alter the FWC, with spatially localized perturbations being an order of magnitude less efficient. Lastly, the authors introduce a novel FWC tendency diagnostic—the Gyre Index—that can be conveniently calculated using observations located only along the gyre boundaries. Its strong predictive capabilities, assessed in the eddy-resolving model forced by stochastic winds, suggest that the Gyre Index would be of use in interpreting FWC evolution in observations as well as in numerical models.

scholarly journals Seasonal and Interannual Variations of Irminger Ring Formation and Boundary–Interior Heat Exchange in FLAME

2016 ◽  
Vol 46 (6) ◽  
pp. 1717-1734 ◽  
Author(s):  
M. F. de Jong ◽  
A. S. Bower ◽  
H. H. Furey
Keyword(s):  
Heat Flux ◽  
Heat Exchange ◽  
Time Variability ◽  
Strongly Correlated ◽  
Boundary Current ◽  
Warm Core ◽  
Convective Region ◽  
Eddy Formation ◽  
Current Instability ◽  
Irminger Current

AbstractThe contribution of warm-core anticyclones shed by the Irminger Current off West Greenland, known as Irminger rings, to the restratification of the upper layers of the Labrador Sea is investigated in the 1/12° Family of Linked Atlantic Models Experiment (FLAME) model. The model output, covering the 1990–2004 period, shows strong similarities to observations of the Irminger Current as well as ring observations at a mooring located offshore of the eddy formation region in 2007–09. An analysis of fluxes in the model shows that while the majority of heat exchange with the interior indeed occurs at the site of the Irminger Current instability, the contribution of the coherent Irminger rings is modest (18%). Heat is provided to the convective region mainly through noncoherent anomalies and enhanced local mixing by the rings facilitating further exchange between the boundary and interior. The time variability of the eddy kinetic energy and the boundary to interior heat flux in the model are strongly correlated to the density gradient between the dense convective region and the more buoyant boundary current. In FLAME, the density variations of the boundary current are larger than those of the convective region, thereby largely controlling changes in lateral fluxes. Synchronous long-term trends in temperature in the boundary and the interior over the 15-yr simulation suggest that the heat flux relative to the temperature of the interior is largely steady on these time scales.

An Investigation of Turbulence Generation Mechanisms above Deep Convection

2003 ◽  
Vol 60 (10) ◽  
pp. 1297-1321 ◽  
Author(s):  
Todd P. Lane ◽  
Robert D. Sharman ◽  
Terry L. Clark ◽  
Hsiao-Ming Hsu
Keyword(s):  
Deep Convection ◽  
Generation Mechanisms ◽  
Turbulence Generation

scholarly journals The Geomorphological Dynamic of the Rupat Strait on the East Coast of Central Sumatera Island, Indonesia

2021 ◽  
Vol 56 (1) ◽  
Author(s):  
Rifardi ◽  
Hafiza Tartila Isty ◽  
Reza Ambar Wati
Keyword(s):  
East Coast ◽  
Current System ◽  
Bottom Topography ◽  
Coarse Grained ◽  
Eastern Coast ◽  
Shallow Marine ◽  
High Wave ◽  
Strong Current ◽  
High Wave Energy ◽  
Malacca Strait

The Rupat Strait on the eastern coast of Sumatera Island is currently undergoing a geomorphological process due to the current system, which flows from the Malacca Strait, and the change of use of the hinterland. The main purpose of this study is to identify the geomorphological dynamic by analyzing the changes to the width and depth of the strait. We propose a remote sensing method using satellite imagery to evaluate the changes to the width and depth. The depth was also measured using echo sounding at 60 stations. The studies of oceanographic observation and sedimentation were carried out along the coastal area of Dumai City and Rupat Island at five stations on each coast. The results showed that although the width of the strait had increased from 6.91 km in 1997 to 7.63 km in 2017, the strait length had not changed over this period. Therefore, the area of the strait increased to 82.544 km² in 20 years from 463.687 km² in 1997 to 544.231 km² in 2017. Over 28 years, the depth of the strait has increased by 1.5–2.7 meters. The changes are due to abrasion and sedimentation, which caused accretion on the coasts of Dumai City and Rupat Island, which go around the Rupat Strait. The abrasion is occupied by a strong current velocity, high-wave energy, steep bottom topography, and coarse-grained sediments, and it was reversed at the accretion areas. The results of this study can be used to guide stakeholders on the utilization and management of shallow marine waters.

scholarly journals Effect of mesoscale eddy on thermocline depth over the global ocean: deepen and uplift

2020 ◽  
Author(s):  
Xiaoyan Chen ◽  
Ge Chen
Keyword(s):  
Satellite Altimetry ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Vertical Displacement ◽  
Ring Structure ◽  
Global Ocean ◽  
Thermocline Depth ◽  
Strong Current ◽  
Current Systems ◽  
Northern And Southern Hemispheres

Abstract. Existing studies on the vertical displacement of thermoclines driven by mesoscale eddies are insufficient and rare. Using 17-year Argo dataset in combination with satellite altimetry, the deepening and uplifting of the depth of thermocline (DTC) by anticyclonic (AE) or cyclonic eddies (CE), respectively, were estimated globally. DTC shifts exhibited multiple geographic and seasonal trends, with the largest magnitude shifts occurring in March and September in the Northern and Southern Hemispheres, respectively. The more pronounced DTC shifts were concentrated in the midlatitudes, and the largest DTC displacements appeared along the western boundaries of strong current systems, with peak shifts of more than 40 m. In general, eddy-induced DTC shifts were linearly correlated with eddy radius and amplitude, suggesting that high intensity eddies induced larger DTC displacements. Finally, a normalized analysis revealed a monopole (ring) structure of DTC ringing the eddy center inside the AE (CE). The forces of AE and CE on the DTC were different, seen in the stronger deepening at the center of the AE (~ 30 m) than the uplifting at the center of the CE (~ 20 m). One possible mechanism for this asymmetry could stem from differential current shears in the thermoclines in AE and CE.

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