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.

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

2012 ◽  
Vol 9 (4) ◽  
pp. 2457-2491 ◽  
Author(s):  
I. Bashmachnikov ◽  
X. Carton
Keyword(s):  
Initial Period ◽  
Sea Surface ◽  
Upper Ocean ◽  
Buoyancy Frequency ◽  
Coriolis Parameter ◽  
Ocean Stratification ◽  
North East ◽  
The North ◽  
Surface Signature ◽  
Mediterranean Water

Abstract. Meddies, intra-thermocline eddies of Mediterranean water, are often visible 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. Then, theoretical estimates of the surface signature of a meddy are derived, based on geostrophy and potential vorticity balance. The intensity of the surface signature is 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. Estimates suggest that the southernmost limit for detection in altimetry of small meddies (with radii on the order of 15 km) should lie in the northern subtropics, while large meddies (with radii of 25–30 km) could be detected as far south as the northern tropics. During the initial period of meddy acceleration after meddy formation or a stagnation stage, a cyclonic signal also is generated at the sea-surface, but mostly the anticyclonic surface signal follows the meddy.

scholarly journals Potential Vorticity Dynamics of Tropical Instability Vortices

2014 ◽  
Vol 44 (3) ◽  
pp. 995-1011 ◽  
Author(s):  
Ryan M. Holmes ◽  
Leif N. Thomas ◽  
LuAnne Thompson ◽  
David Darr
Keyword(s):  
Potential Vorticity ◽  
Relative Vorticity ◽  
Equatorial Region ◽  
Equatorial Pacific ◽  
Vertical Shear ◽  
Coriolis Parameter ◽  
Equatorial Undercurrent ◽  
North Equatorial Counter Current ◽  
Lateral Mixing ◽  
Counter Current

Abstract Tropical instability vortices (TIVs) in the equatorial Pacific exhibit energetic horizontal and vertical circulation characterized by regions of high Rossby number and low Richardson number. Their strong anticyclonic vorticity and vertical shear can influence the broader-scale circulation by driving lateral mixing and vertical exchange between the ocean surface and interior. The authors use a set of nested high-resolution simulations of the equatorial Pacific, with a finest grid size of 3 km, to examine the vortex dynamics associated with TIV core water formation. TIV cores are characterized by low values of the Ertel potential vorticity (PV) as the relative vorticity is anticyclonic with magnitude comparable to the local Coriolis parameter. A study of the variation of PV and other scalars along Lagrangian fluid parcel tracks entering the TIVs shows that the low-PV water in their cores is a mix of Equatorial Undercurrent (EUC) water and North Equatorial Counter Current (NECC) water. The EUC water is characterized by strong horizontal vorticity, and thus, the baroclinic component of the PV is nonnegligible and acts as a source for the anticyclonic vorticity of TIVs. This horizontal vorticity is tilted by an ageostrophic secondary circulation associated with strain-induced frontogenesis that tends to form along the path of the EUC water that enters the vortex. Frontogenesis disrupts the cyclogeostrophic balance of the frontal flow and drives differential vertical motions across the front. These results emphasize the role of submesoscale physics in the equatorial region, which are active when both the Rossby and Richardson numbers are O(1).

scholarly journals Deglacial development of (sub) sea surface temperature and salinity in the subarctic northwest Pacific: Implications for upper-ocean stratification

2013 ◽  
Vol 28 (1) ◽  
pp. 91-104 ◽  
Author(s):  
Jan-Rainer Riethdorf ◽  
Lars Max ◽  
Dirk Nürnberg ◽  
Lester Lembke-Jene ◽  
Ralf Tiedemann
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Upper Ocean ◽  
Northwest Pacific ◽  
Ocean Stratification

The instability and breakdown of tall columnar vortices in a quasi-geostrophic fluid

1996 ◽  
Vol 328 ◽  
pp. 129-160 ◽  
Author(s):  
David G. Dritschel ◽  
Manuel De La Torre JuáRez
Keyword(s):  
Potential Vorticity ◽  
Baroclinic Instability ◽  
Three Dimensional ◽  
Lower Surface ◽  
Buoyancy Frequency ◽  
Coriolis Parameter ◽  
Nonlinear Development ◽  
Aspect Ratios ◽  
Geostrophic Turbulence ◽  
Boussinesq Fluid

We examine the linear stability of elliptical columns of uniform potential vorticity subject to two-dimensional (horizontal) straining within a rapidly rotating, stratified (quasi-geostrophic) fluid. We find that horizontal straining can promote the exponential growth of three-dimensional disturbances when the vortex height-to-width aspect ratio exceeds, qualitatively, three times the ratio of the Coriolis parameter to the buoyancy frequency. This instability is not related to the usual baroclinic instability which operates on shallow vortex columns whose potential vorticity changes sign with height. The nonlinear development of these instabilities is investigated numerically using a high-resolution contour surgery algorithm. Simulations are conducted for both a Boussinesq (ocean-like) fluid and a compressible (atmospheric-like) fluid having exponentially decreasing density with height. The simulations reveal a generic nonlinear development that results in a semi-ellipsoidal baroclinic vortex dome at the lower surface and, in the case of a Boussinesq fluid, another such dome at the upper surface.The related problem of two interacting vortex columns is also examined. A generic three-dimensional instability and nonlinear development occurs no matter how great the distance between the vortex columns, provided that they are sufficiently tall.Our results may bear upon the observed structure of many atmospheric and oceanic vortices, whose height-to-width aspect ratios are consistent with our findings. Remarkably, even strongly ageostrophic vortices, such as tropical cyclones, fit the pattern. Our results furthermore re-open questions about the long-time nature of freely decaying quasi-geostrophic turbulence, for which recent simulations indicate a progressive two-dimensionalization by vortex alignment, while earlier simulations have indicated long-lived baroclinic vortices, not unlike what we find here.

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 Reconstructability of Three-Dimensional Upper-Ocean Circulation from SWOT Sea Surface Height Measurements

2016 ◽  
Vol 46 (3) ◽  
pp. 947-963 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen ◽  
Patrice Klein ◽  
Clement Ubelmann ◽  
Lee-Lueng Fu ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Measurement Errors ◽  
Kuroshio Extension ◽  
Three Dimensional ◽  
Sea Surface Height ◽  
Relative Vorticity ◽  
Sea Surface ◽  
Upper Ocean ◽  
Model Output ◽  
Satellite Mission

AbstractUtilizing the framework of effective surface quasigeostrophic (eSQG) theory, this study explores the potential of reconstructing the 3D upper-ocean circulation structures, including the balanced vertical velocity w field, from high-resolution sea surface height (SSH) data of the planned Surface Water and Ocean Topography (SWOT) satellite mission. Specifically, the authors utilize the 1/30°, submesoscale-resolving, OFES model output and subject it to the SWOT simulator that generates the along-swath SSH data with expected measurement errors. Focusing on the Kuroshio Extension region in the North Pacific where regional Rossby numbers range from 0.22 to 0.32, this study finds that the eSQG dynamics constitute an effective framework for reconstructing the 3D upper-ocean circulation field. Using the modeled SSH data as input, the eSQG-reconstructed relative vorticity ζ and w fields are found to reach a correlation of 0.7–0.9 and 0.6–0.7, respectively, in the 1000-m upper ocean when compared to the original model output. Degradation due to the SWOT sampling and measurement errors in the input SSH data for the ζ and w reconstructions is found to be moderate, 5%–25% for the 3D ζ field and 15%–35% for the 3D w field. There exists a tendency for this degradation ratio to decrease in regions where the regional eddy variability (or Rossby number) increases.

scholarly journals Summertime increases in upper-ocean stratification and mixed-layer depth

Nature ◽  
2021 ◽  
Vol 591 (7851) ◽  
pp. 592-598
Author(s):  
Jean-Baptiste Sallée ◽  
Violaine Pellichero ◽  
Camille Akhoudas ◽  
Etienne Pauthenet ◽  
Lucie Vignes ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Upper Ocean ◽  
Layer Depth ◽  
Ocean Stratification

scholarly journals A Note on the Numerical Representation of Surface Dynamics in Quasigeostrophic Turbulence: Application to the Nonlinear Eady Model

2009 ◽  
Vol 66 (4) ◽  
pp. 1063-1068 ◽  
Author(s):  
Ross Tulloch ◽  
K. Shafer Smith
Keyword(s):  
Numerical Models ◽  
Buoyancy Frequency ◽  
Complete Suppression ◽  
Numerical Representation ◽  
Vertical Resolution ◽  
Surface Dynamics ◽  
Coriolis Parameter ◽  
Theoretical Predictions ◽  
Vertical Grid ◽  
Similar Restriction

Abstract The quasigeostrophic equations consist of the advection of linearized potential vorticity coupled with advection of temperature at the bounding upper and lower surfaces. Numerical models of quasigeostrophic flow often employ greater (scaled) resolution in the horizontal than in the vertical (the two-layer model is an extreme example). In the interior, this has the effect of suppressing interactions between layers at horizontal scales that are small compared to Nδz/f (where δz is the vertical resolution, N the buoyancy frequency, and f the Coriolis parameter). The nature of the turbulent cascade in the interior is, however, not fundamentally altered because the downscale cascade of potential enstrophy in quasigeostrophic turbulence and the downscale cascade of enstrophy in two-dimensional turbulence (occurring layerwise) both yield energy spectra with slopes of −3. It is shown here that a similar restriction on the vertical resolution applies to the representation of horizontal motions at the surfaces, but the penalty for underresolving in the vertical is complete suppression of the surface temperature cascade at small scales and a corresponding artificial steepening of the surface energy spectrum. This effect is demonstrated in the nonlinear Eady model, using a finite-difference representation in comparison with a model that explicitly advects temperature at the upper and lower surfaces. Theoretical predictions for the spectrum of turbulence in the nonlinear Eady model are reviewed and compared to the simulated flows, showing that the latter model yields an accurate representation of the cascade dynamics. To accurately represent dynamics at horizontal wavenumber K in the vertically finite-differenced model, it is found that the vertical grid spacing must satisfy δz ≲ 0.3f/(NK); at wavenumbers K > 0.3f/(Nδz), the spectrum of temperature variance rolls off rapidly.

scholarly journals Multi-symplectic formulation of near-local Hamiltonian balanced models

2011 ◽  
Vol 467 (2136) ◽  
pp. 3424-3442 ◽  
Author(s):  
Sylvain Delahaies ◽  
Peter E. Hydon
Keyword(s):  
Potential Vorticity ◽  
Contact Structure ◽  
Fluid Motion ◽  
Local Model ◽  
Contact Transformation ◽  
Geometric Features ◽  
Coriolis Parameter ◽  
New Class

We transform near-local Hamiltonian balanced models (HBMs) describing nearly geostrophic fluid motion (with constant Coriolis parameter) into multi-symplectic (MS) systems. This allows us to determine conservation of Lagrangian momentum, energy and potential vorticity for Salmon's L 1 dynamics; a similar approach works for other near-local balanced models (such as the -model). The MS approach also enables us to determine a class of systems that have a contact structure similar to that of the semigeostrophic model. The contact structure yields a contact transformation that makes the problem of front formation tractable. The new class includes the first local model with a variable Coriolis parameter that preserves all of the most useful geometric features of the semigeostrophic model.

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