Adiabatic Eastern Boundary Currents

2013 ◽  
Vol 43 (6) ◽  
pp. 1127-1149 ◽  
Author(s):  
Paola Cessi ◽  
Christopher L. Wolfe
Keyword(s):  
Potential Vorticity ◽  
Relative Vorticity ◽  
Oceanic Circulation ◽  
Boundary Current ◽  
Coriolis Parameter ◽  
Mean Velocity ◽  
Eastern Boundary ◽  
Eastern Boundary Current ◽  
Eddy Fluxes ◽  
The Mean

Abstract The dynamics of the eastern boundary current of a high-resolution, idealized model of oceanic circulation are analyzed and interpreted in terms of residual mean theory. In this framework, it is clear that the eastern boundary current is adiabatic and inviscid. Nevertheless, the time-averaged potential vorticity is not conserved along averaged streamlines because of the divergence of Eliassen–Palm fluxes, associated with buoyancy and momentum eddy fluxes. In particular, eddy fluxes of buoyancy completely cancel the mean downwelling or upwelling, so that there is no net diapycnal residual transport. The eddy momentum flux acts like a drag on the mean velocity, opposing the acceleration from the eddy buoyancy flux: in the potential vorticity budget this results in a balance between the divergences of eddy relative vorticity and buoyancy fluxes, which leads to a baroclinic eastern boundary current whose horizontal scale is the Rossby deformation radius and whose vertical extent depends on the eddy buoyancy transport, the Coriolis parameter, and the mean surface buoyancy distribution.

scholarly journals Diagnosing the Influence of Mesoscale Eddy Fluxes on the Deep Western Boundary Current in the 1/10° STORM/NCEP Simulation

2019 ◽  
Vol 49 (3) ◽  
pp. 751-764 ◽  
Author(s):  
Veit Lüschow ◽  
Jin-Song von Storch ◽  
Jochem Marotzke
Keyword(s):  
Potential Energy ◽  
Mesoscale Eddy ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
Mean Flow ◽  
Coriolis Parameter ◽  
Deep Western Boundary Current ◽  
Eddy Fluxes ◽  
The Mean

AbstractUsing a 0.1° ocean model, this paper establishes a consistent picture of the interaction of mesoscale eddy density fluxes with the geostrophic deep western boundary current (DWBC) in the Atlantic between 26°N and 20°S. Above the DWBC core (the level of maximum southward flow, ~2000-m depth), the eddies flatten isopycnals and hence decrease the potential energy of the mean flow, which agrees with their interpretation and parameterization in the Gent–McWilliams framework. Below the core, even though the eddy fluxes have a weaker magnitude, they systematically steepen isopycnals and thus feed potential energy to the mean flow, which contradicts common expectations. These two vertically separated eddy regimes are found through an analysis of the eddy density flux divergence in stream-following coordinates. In addition, pathways of potential energy in terms of the Lorenz energy cycle reveal this regime shift. The twofold eddy effect on density is balanced by an overturning in the plane normal to the DWBC. Its direction is clockwise (with upwelling close to the shore and downwelling further offshore) north of the equator. In agreement with the sign change in the Coriolis parameter, the overturning changes direction to anticlockwise south of the equator. Within the domain covered in this study, except in a narrow band around the equator, this scenario is robust along the DWBC.

Mapping Jets and Eddies in an Eastern Boundary Current

1997 ◽  
Author(s):  
Adriana Huyer ◽  
P. M. Kosro ◽  
Jack A. Barth ◽  
Robert L. Smith
Keyword(s):  
Boundary Current ◽  
Eastern Boundary ◽  
Eastern Boundary Current

scholarly journals Radiating Instability of a Meridional Boundary Current

2008 ◽  
Vol 38 (10) ◽  
pp. 2294-2307 ◽  
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.

scholarly journals Surface signature of Mediterranean water eddies in the Northeastern Atlantic: effect of the upper ocean stratification

Ocean Science ◽  
2012 ◽  
Vol 8 (6) ◽  
pp. 931-943 ◽  
Author(s):  
I. Bashmachnikov ◽  
X. Carton
Keyword(s):  
Potential Vorticity ◽  
Initial Period ◽  
Relative Vorticity ◽  
Sea Surface ◽  
Upper Ocean ◽  
Buoyancy Frequency ◽  
Coriolis Parameter ◽  
Ocean Stratification ◽  
Surface Signature ◽  
Mediterranean Water

Abstract. Meddies, intra-thermocline eddies of Mediterranean water, can often be detected at the sea surface as positive sea-level anomalies. Here we study the surface signature of several meddies tracked with RAFOS floats and AVISO altimetry. While pushing its way through the water column, a meddy raises isopycnals above. As a consequence of potential vorticity conservation, negative relative vorticity is generated in the upper layer. During the initial period of meddy acceleration after meddy formation or after a stagnation stage, a cyclonic signal is also generated at the sea-surface, but mostly the anticyclonic surface signal follows the meddy. Based on geostrophy and potential vorticity balance, we present theoretical estimates of the intensity of the surface signature. It appears to be proportional to the meddy core radius and to the Coriolis parameter, and inversely proportional to the core depth and buoyancy frequency. This indicates that surface signature of a meddy may be strongly reduced by the upper ocean stratification. Using climatic distribution of the stratification intensity, we claim that the southernmost limit for detection in altimetry of small meddies (with radii on the order of 10–15 km) should lie in the subtropics (35–45° N), while large meddies (with radii of 25–30 km) could be detected as far south as the northern tropics (25–35° N). Those results agree with observations.

Sinking particle fluxes from the euphotic zone over the continental slope of an eastern boundary current region

1996 ◽  
Vol 54 (6) ◽  
pp. 1097-1122 ◽  
Author(s):  
M. A. Pena ◽  
K. L. Denman ◽  
J. R. Forbes ◽  
S. E. Calvert ◽  
R. E. Thomson
Keyword(s):  
Continental Slope ◽  
Euphotic Zone ◽  
Boundary Current ◽  
Eastern Boundary ◽  
Eastern Boundary Current ◽  
Current Region ◽  
Particle Fluxes

Climate change and wind intensification in coastal upwelling ecosystems

Science ◽  
2014 ◽  
Vol 345 (6192) ◽  
pp. 77-80 ◽  
Author(s):  
W. J. Sydeman ◽  
M. García-Reyes ◽  
D. S. Schoeman ◽  
R. R. Rykaczewski ◽  
S. A. Thompson ◽  
...  
Keyword(s):  
Climate Change ◽  
Coastal Upwelling ◽  
Meta Analysis ◽  
Boundary Current ◽  
Eastern Boundary ◽  
Warming Pattern ◽  
Eastern Boundary Current ◽  
Coastal Winds ◽  
Variable Support ◽  
Current Systems

In 1990, Andrew Bakun proposed that increasing greenhouse gas concentrations would force intensification of upwelling-favorable winds in eastern boundary current systems that contribute substantial services to society. Because there is considerable disagreement about whether contemporary wind trends support Bakun’s hypothesis, we performed a meta-analysis of the literature on upwelling-favorable wind intensification. The preponderance of published analyses suggests that winds have intensified in the California, Benguela, and Humboldt upwelling systems and weakened in the Iberian system over time scales ranging up to 60 years; wind change is equivocal in the Canary system. Stronger intensification signals are observed at higher latitudes, consistent with the warming pattern associated with climate change. Overall, reported changes in coastal winds, although subtle and spatially variable, support Bakun’s hypothesis of upwelling intensification in eastern boundary current systems.

scholarly journals Influence of Bottom Topography on Integral Constraints in Zonal Flows with Parameterized Potential Vorticity Fluxes

2013 ◽  
Vol 43 (2) ◽  
pp. 311-323 ◽  
Author(s):  
V. O. Ivchenko ◽  
B. Sinha ◽  
V. B. Zalesny ◽  
R. Marsh ◽  
A. T. Blaker
Keyword(s):  
Potential Vorticity ◽  
Bottom Topography ◽  
Momentum Conservation ◽  
Integral Constraint ◽  
Mean Flow ◽  
Transfer Coefficients ◽  
Flat Bottom ◽  
Zonal Flows ◽  
Eddy Fluxes ◽  
The Mean

Abstract An integral constraint for eddy fluxes of potential vorticity (PV), corresponding to global momentum conservation, is applied to two-layer zonal quasigeostrophic channel flow. This constraint must be satisfied for any type of parameterization of eddy PV fluxes. Bottom topography strongly influences the integral constraint compared to a flat bottom channel. An analytical solution for the mean flow solution has been found by using asymptotic expansion in a small parameter, which is the ratio of the Rossby radius to the meridional extent of the channel. Applying the integral constraint to this solution, one can find restrictions for eddy PV transfer coefficients that relate the eddy fluxes of PV to the mean flow. These restrictions strongly deviate from restrictions for the channel with flat bottom topography.

scholarly journals Detiding Shipboard ADCP Data in Eastern Boundary Current

2011 ◽  
Vol 28 (1) ◽  
pp. 94-103 ◽  
Author(s):  
Heriberto Jesus Vazquez ◽  
Jose Gomez-Valdes ◽  
Modesto Ortiz ◽  
Juan Adolfo Dworak
Keyword(s):  
Least Squares ◽  
Baja California ◽  
Gaussian Function ◽  
Kelvin Wave ◽  
Boundary Current ◽  
Mean Flow ◽  
Wave Dynamics ◽  
Eastern Boundary ◽  
Eastern Boundary Current ◽  
Adcp Data

Abstract Spatiotemporal fitting by the least squares method is commonly applied to distinguish the mean flow from the tidal current from shipboard ADCP data in coastal ocean. To analyze this technique in a pelagic region of an eastern boundary current system, a 6-yr period of shipboard ADCP data off Baja California is examined. A diverse set of basis functions is studied and a global tidal model is used for comparison purposes. The Gaussian function together with a nodal configuration of one node in the middle and close to the coast of the region is the best option. However, to obtain the optimal solution, the geostrophic flow, which is stronger than the tidal flow and highly variable off Baja California, might be removed prior to fitting the data. In general, the semimajor axis of the tidal ellipse (M2) is parallel to the coast and the phase speed is poleward and parallel to the coast, in agreement with Kelvin wave dynamics. Because the tides in eastern boundary currents are explained by Kelvin wave dynamics, the use of both the velocity field without geostrophic variability and the Gaussian function in the spatiotemporal fitting by least squares technique is a promising tool for detiding shipboard ADCP data from these systems.

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