Numerical assessments of ocean energy extraction from western boundary currents using a quasi-geostrophic ocean circulation model

Abstract A global ocean circulation model is formulated in terms of the “residual mean” and used to study eddy–mean flow interaction. Adjoint techniques are used to compute the three-dimensional eddy stress field that minimizes the departure of the coarse-resolution model from climatological observations of temperature. The resulting 3D maps of eddy stress and residual-mean circulation yield a wealth of information about the role of eddies in large-scale ocean circulation. In eddy-rich regions such as the Southern Ocean, the Kuroshio, and the Gulf Stream, eddy stresses have an amplitude comparable to the wind stress, of order 0.2 N m−2, and carry momentum from the surface down to the bottom, where they are balanced by mountain form drag. From the optimized eddy stress, 3D maps of horizontal eddy diffusivity κ are inferred. The diffusivities have a well-defined large-scale structure whose prominent features are 1) large values of κ (up to 4000 m2 s−1) in the western boundary currents and on the equatorial flank of the Antarctic Circumpolar Current and 2) a surface intensification of κ, suggestive of a dependence on the stratification N 2. It is shown that implementation of an eddy parameterization scheme in which the eddy diffusivity has an N 2 dependence significantly improves the climatology of the ocean model state relative to that obtained using a spatially uniform diffusivity.

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A novel masking technique to investigate atmosphere-ocean interaction over Western Boundary Currents

10.5194/egusphere-egu2020-9721 ◽

2020 ◽

Author(s):

Fumi Hayashi

Keyword(s):

Gulf Stream ◽

General Circulation ◽

Circulation Model ◽

Western Boundary ◽

Atmospheric Response ◽

Low Resolution ◽

Western Boundary Currents ◽

Boundary Currents ◽

Oceanic Fronts ◽

The Difference

<p>Western Boundary Currents (WBC), such as the Gulf Stream, leave a strong imprint on the ocean-atmosphere boundary in the form of strong gradients and high variability of Sea Surface Temperature (SST). Recent studies have shown that midlatitude oceanic fronts have an influence throughout the depth of the troposphere by means of synoptic systems such as weather fronts. An understanding of how the midlatitude ocean influences the synoptic system is crucial for better climate projection, however, this has been challenging. For example, in model simulations the sensitivity of the atmosphere to SST anomalies are dependent on its resolution, with low resolution models unable to capture the air-sea interactions occurring over warm sectors of midlatitude cyclones, possibly leading to underestimations of the oceanic influence on the atmosphere. A novel modelling technique is developed in which an interactive &#8220;mask&#8221; is used to systematically isolate and study the air-sea interaction over different synoptic regimes (warm and cold sector). Here, simulations using an idealised aqua-planet atmospheric general circulation model (AGCM) are used to study the atmospheric response to a tightening of SST gradient (comparable to that of the Gulf Stream) over the cold sector (&#8220;cold path&#8221;) and the warm sector (&#8220;warm path&#8221;) separately. Same experiments will also be performed on models with higher resolution to investigate the difference in atmospheric response between the high and low resolution models and what physical processes are responsible for such change in response.</p>

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Response of the Inertial Recirculation to Intensified Stratification in a Two-Layer Quasigeostrophic Ocean Circulation Model

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0111.1 ◽

2013 ◽

Vol 43 (7) ◽

pp. 1254-1269 ◽

Cited By ~ 13

Author(s):

Shantong Sun ◽

Lixin Wu ◽

Bo Qiu

Keyword(s):

Surface Layer ◽

Ocean Circulation ◽

Circulation Model ◽

Surface Flow ◽

Western Boundary ◽

Barotropic Instability ◽

Boundary Current ◽

Ocean Circulation Model ◽

Model Studies ◽

Budget Analysis

Abstract Previous observation and model studies show that the upper-ocean stratification is enhanced under global warming (Capotondi et al.; Cravatte et al.; Deser et al., etc.). The response of the recirculation, which is associated with the western boundary current (WBC) jet extension and significantly increases its transport, to the intensified stratification, is studied in a two-layer quasigeostrophic ocean circulation model. It is found that the barotropic transport of the circulation first increases with stratification but then decreases as a result of saturation of the surface-layer circulation intensity when the stratification exceeds a threshold. PV budget analysis indicates that the saturation is caused by the increased intergyre transport of relative potential vorticity resulting from the intensified variability of the jet location. Both the barotropic instability and bifurcation mechanisms contribute to the intensified variability of the jet location. Because of barotropic instability, eddies are generated in the confluence region of the WBCs and advected eastward, causing the variability of the jet location. With increased stratification, the surface-layer circulation is strengthened and the barotropic instability is intensified. As a result, the surface flow becomes more variable with excessive eddies and intense variability of the jet. With the increasing stratification, three regimes, each marked by its own variation of the jet location, emerge owing to the successive system bifurcations. In the last two regimes, variability of the jet location is further enhanced by frequent switches among the different dynamic states on multidecadal time scales.

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Incorporation of Surface Wave Effects into a Coastal Ocean Circulation Model

10.21236/ada629884 ◽

1999 ◽

Author(s):

Lian Xie ◽

Leonard J. Pietrafesa

Keyword(s):

Surface Wave ◽

Ocean Circulation ◽

Circulation Model ◽

Coastal Ocean ◽

Ocean Circulation Model ◽

Coastal Ocean Circulation ◽

Wave Effects ◽

Coastal Ocean Circulation Model

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Radiating Instability of a Meridional Boundary Current

Journal of Physical Oceanography ◽

10.1175/2008jpo3853.1 ◽

2008 ◽

Vol 38 (10) ◽

pp. 2294-2307 ◽

Cited By ~ 26

Author(s):

Hristina G. Hristova ◽

Joseph Pedlosky ◽

Michael A. Spall

Keyword(s):

Western Boundary ◽

Far Field ◽

Boundary Current ◽

Important Conclusion ◽

Western Boundary Currents ◽

Horizontal Structure ◽

Boundary Currents ◽

Zonal Jets ◽

Eastern Boundary ◽

Eastern Boundary Current

Abstract A linear stability analysis of a meridional boundary current on the beta plane is presented. The boundary current is idealized as a constant-speed meridional jet adjacent to a semi-infinite motionless far field. The far-field region can be situated either on the eastern or the western side of the jet, representing a western or an eastern boundary current, respectively. It is found that when unstable, the meridional boundary current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field. This is the so-called radiating instability and is found in both barotropic and two-layer baroclinic configurations. A second but important conclusion concerns the differences in the stability properties of eastern and western boundary currents. An eastern boundary current supports a greater number of radiating modes over a wider range of meridional wavenumbers. It generates waves with amplitude envelopes that decay slowly with distance from the current. The radiating waves tend to have an asymmetrical horizontal structure—they are much longer in the zonal direction than in the meridional, a consequence of which is that unstable eastern boundary currents, unlike western boundary currents, have the potential to act as a source of zonal jets for the interior of the ocean.

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