scholarly journals Is the Coefficient of Eddy Potential Vorticity Diffusion Positive? Part I: Barotropic Zonal Channel

2018 ◽  
Vol 48 (7) ◽  
pp. 1589-1607 ◽  
Author(s):  
V. O. Ivchenko ◽  
V. B. Zalesny ◽  
B. Sinha
Keyword(s):  
Potential Vorticity ◽  
Independent Solution ◽  
Zonal Flow ◽  
Momentum Balance ◽  
Eddy Fluxes ◽  
The Mean ◽  
Zonal Momentum Balance ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Zonal Momentum

AbstractThe question of whether the coefficient of diffusivity of potential vorticity by mesoscale eddies is positive is studied for a zonally reentrant barotropic channel using the quasigeostrophic approach. The topography is limited to the first mode in the meridional direction but is unlimited in the zonal direction. We derive an analytic solution for the stationary (time independent) solution. New terms associated with parameterized eddy fluxes of potential vorticity appear both in the equations for the mean zonal momentum balance and in the kinetic energy balance. These terms are linked with the topographic form stress exerted by parameterized eddies. It is demonstrated that in regimes with zonal flow (analogous to the Antarctic Circumpolar Current), the coefficient of eddy potential vorticity diffusivity must be positive.

scholarly journals Zonal Momentum Balance, Potential Vorticity Dynamics, and Mass Fluxes on Near-Surface Isentropes

2005 ◽  
Vol 62 (6) ◽  
pp. 1884-1900 ◽  
Author(s):  
Tapio Schneider
Keyword(s):  
Potential Vorticity ◽  
Momentum Balance ◽  
Near Surface ◽  
Global Circulation ◽  
Balance Condition ◽  
Mass Fluxes ◽  
Vorticity Dynamics ◽  
The Mean ◽  
Zonal Momentum Balance ◽  
Zonal Momentum

Abstract While it has been recognized for some time that isentropic coordinates provide a convenient framework for theories of the global circulation of the atmosphere, the role of boundary effects in the zonal momentum balance and in potential vorticity dynamics on isentropes that intersect the surface has remained unclear. Here, a balance equation is derived that describes the temporal and zonal mean balance of zonal momentum and of potential vorticity on isentropes, including the near-surface isentropes that sometimes intersect the surface. Integrated vertically, the mean zonal momentum or potential vorticity balance leads to a balance condition that relates the mean meridional mass flux along isentropes to eddy fluxes of potential vorticity and surface potential temperature. The isentropic-coordinate balance condition formally resembles balance conditions well known in quasigeostrophic theory, but on near-surface isentropes it generally differs from the quasigeostrophic balance conditions. Not taking the intersection of isentropes with the surface into account, quasigeostrophic theory does not adequately represent the potential vorticity dynamics and mass fluxes on near-surface isentropes—a shortcoming that calls into question the relevance of quasigeostrophic theories for the macroturbulence and global circulation of the atmosphere.

scholarly journals Acceleration of the Antarctic Circumpolar Current by Wind Stress along the Coast of Antarctica

2013 ◽  
Vol 43 (12) ◽  
pp. 2772-2784 ◽  
Author(s):  
Jan D. Zika ◽  
Julien Le Sommer ◽  
Carolina O. Dufour ◽  
Alberto Naveira-Garabato ◽  
Adam Blaker
Keyword(s):  
Antarctic Circumpolar Current ◽  
Momentum Balance ◽  
Quasi Equilibrium ◽  
Two Factors ◽  
Free Mode ◽  
Zonal Momentum Balance ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Balance Mechanism ◽  
Zonal Momentum

Abstract The influence of wind forcing on variability of the Antarctic Circumpolar Current (ACC) is investigated using a series of eddy-permitting ocean–sea ice models. At interannual and decadal time scales the ACC transport is sensitive to both the mean strength of westerly winds along the ACC circumpolar path, consistent with zonal momentum balance theories, and sensitive to the wind stresses along the coast of Antarctica, consistent with the “free mode” theory of Hughes et al. A linear combination of the two factors explains differences in ACC transport across 11 regional quasi-equilibrium experiments. Repeated single-year global experiments show that the ACC can be robustly accelerated by both processes. Across an ensemble of simulations with realistic forcing over the second half of the twentieth century, interannual ACC transport variability owing to the free-mode mechanism exceeds that due to the zonal momentum balance mechanism by a factor of between 3.5 and 5 to one. While the ACC transport may not accelerate significantly owing to projected increases in along-ACC winds in future decades, significant changes in transport could still occur because of changes in the stress along the coast of Antarctica.

scholarly journals Reshaping the Antarctic Circumpolar Current via Antarctic Bottom Water Export

2017 ◽  
Vol 47 (10) ◽  
pp. 2577-2601 ◽  
Author(s):  
Andrew L. Stewart ◽  
Andrew McC. Hogg
Keyword(s):  
Antarctic Circumpolar Current ◽  
Bottom Water ◽  
Channel Model ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
Momentum Balance ◽  
Antarctic Bottom Water ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Zonal Momentum

AbstractZonal momentum input into the Antarctic Circumpolar Current (ACC) by westerly winds is ultimately removed via topographic form stress induced by large bathymetric features that obstruct the path of the current. These bathymetric features also support the export of Antarctic Bottom Water (AABW) across the ACC via deep, geostrophically balanced, northward flows. These deep geostrophic currents modify the topographic form stress, implying that changes in AABW export will alter the ocean bottom pressure and require a rearrangement of the ACC in order to preserve its zonal momentum balance. A conceptual model of the ACC momentum balance is used to derive a relationship between the volume export of AABW and the shape of the sea surface across the ACC’s standing meanders. This prediction is tested using an idealized eddy-resolving ACC/Antarctic shelf channel model that includes both the upper and lower cells of the Southern Ocean meridional overturning circulation, using two different topographic configurations to obstruct the flow of the ACC. Eliminating AABW production leads to a shallowing of the sea surface elevation within the standing meander. To quantify this response, the authors introduce the “surface-induced topographic form stress,” the topographic form stress that would result from the shape of the sea surface if the ocean were barotropic. Eliminating AABW production also reduces the magnitude of the eddy kinetic energy generated downstream of the meander and the surface speed of the ACC within the meander. These findings raise the possibility that ongoing changes in AABW export may be detectable via satellite altimetry.

scholarly journals Eddy Phase Speeds in a Two-Layer Model of Quasigeostrophic Baroclinic Turbulence with Applications to Ocean Observations

2016 ◽  
Vol 46 (6) ◽  
pp. 1963-1985 ◽  
Author(s):  
Lei Wang ◽  
Malte Jansen ◽  
Ryan Abernathey
Keyword(s):  
Practical Importance ◽  
Phase Speed ◽  
Wave Theory ◽  
Inverse Cascade ◽  
Barotropic Mode ◽  
Eddy Fluxes ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Ocean Observations ◽  
Shed Light

AbstractThe phase speed spectrum of ocean mesoscale eddies is fundamental to understanding turbulent baroclinic flows. Since eddy phase propagation has been shown to modulate eddy fluxes, an understanding of eddy phase speeds is also of practical importance for the development of improved eddy parameterizations for coarse resolution ocean models. However, it is not totally clear whether and how linear Rossby wave theory can be used to explain the phase speed spectra in various weakly turbulent flow regimes. Using linear analysis, theoretical constraints are identified that control the eddy phase speed in a two-layer quasigeostrophic (QG) model. These constraints are then verified in a series of nonlinear two-layer QG simulations, spanning a range of parameters with potential relevance to the ocean. In the two-layer QG model, the strength of the inverse cascade exerts an important control on the eddy phase speed. If the inverse cascade is weak, the phase speed spectrum is reasonably well approximated by the phase speed of the linearly most unstable mode. A significant inverse cascade instead leads to barotropization, which in turn leads to mean phase speeds closer to those of barotropic-mode Rossby waves. The two-layer QG results are qualitatively consistent with the observed eddy phase speed spectra in the Antarctic Circumpolar Current and may also shed light on the interpretation of phase speed spectra observed in other regions.

scholarly journals A finite-difference convective model for Jupiter's equatorial jet

2006 ◽  
Vol 2 (S239) ◽  
pp. 230-232 ◽  
Author(s):  
Kwing L. Chan
Keyword(s):  
Reynolds Number ◽  
Numerical Model ◽  
Finite Difference ◽  
Spherical Shell ◽  
Reynolds Stress ◽  
Momentum Equation ◽  
Momentum Balance ◽  
Zonal Momentum Balance ◽  
Zonal Momentum ◽  
Convective Model

AbstractWe present results of a numerical model for studying the dynamics of Jupiter's equatorial jet. The computed domain is a piece of spherical shell around the equator. The bulk of the region is convective, with a thin radiative layer at the top. The shell is spinning fast, with a Coriolis number = ΩL/V on the order of 50. A prominent super-rotating equatorial jet is generated, and secondary alternating jets appear in the higher latitudes. The roles of terms in the zonal momentum equation are analyzed. Since both the Reynolds number and the Taylor number are large, the viscous terms are small. The zonal momentum balance is primarily between the Coriolis and the Reynolds stress terms.

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.

The Antarctic circumpolar current and Convergence

1964 ◽  
Vol 281 (1384) ◽  
pp. 14-21 ◽  
Keyword(s):  
Antarctic Circumpolar Current ◽  
Zonal Flow ◽  
The Other ◽  
Convergence Zone ◽  
Circumpolar Current ◽  
The Antarctic

This review of work on the circumpolar current and Convergence will indicate that a number of hypotheses have been advanced, each claiming to have some support from the observations and each differing considerably in their premises. Thus on one side departures from purely zonal flow along lines of latitude are all important, on the other such departures are irrelevant. It will be seen that none of the hypotheses suggest the formation of the marked Convergence zone that has been described by Deacon and in that respect they fail, for the dynamics of the flow should contain a description of the Convergence. It is worth while to describe these hypotheses briefly and see in what respects they are successful and where they fail.

scholarly journals Time-Mean Flow as the Prevailing Contribution to the Poleward Heat Flux across the Southern Flank of the Antarctic Circumpolar Current: A Case Study in the Fawn Trough, Kerguelen Plateau

2013 ◽  
Vol 43 (3) ◽  
pp. 583-601 ◽  
Author(s):  
H. Sekma ◽  
Y.-H. Park ◽  
F. Vivier
Keyword(s):  
Heat Flux ◽  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Mean Flow ◽  
Kerguelen Plateau ◽  
The Mean ◽  
The Cross ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Southern Flank

Abstract The major mechanisms of the oceanic poleward heat flux in the Southern Ocean are still in debate. The long-standing belief stipulates that the poleward heat flux across the Antarctic Circumpolar Current (ACC) is mainly due to mesoscale transient eddies and the cross-stream heat flux by time-mean flow is insignificant. This belief has recently been challenged by several numerical modeling studies, which stress the importance of mean flow for the meridional heat flux in the Southern Ocean. Here, this study analyzes moored current meter data obtained recently in the Fawn Trough, Kerguelen Plateau, to estimate the cross-stream heat flux caused by the time-mean flow and transient eddies. It is shown that the poleward eddy heat flux in this southern part of the ACC is negligible, while that from the mean flow is overwhelming by two orders of magnitude. This is due to the unusual anticlockwise turning of currents with decreasing depth, which is associated with significant bottom upwelling engendered by strong bottom currents flowing over the sloping topography of the trough. The circumpolar implications of these local observations are discussed in terms of the depth-integrated linear vorticity budget, which suggests that the six topographic features along the southern flank of the ACC equivalent to the Fawn Trough case would yield sufficient poleward heat flux to balance the oceanic heat loss in the subpolar region. As eddy activity on the southern flank of the ACC is too weak to transport sufficient heat poleward, the nonequivalent barotropic structure of the mean flow in several topographically constricted passages should accomplish the required task.

Zonal Momentum Balance at the Equator

1989 ◽  
Vol 19 (5) ◽  
pp. 561-570 ◽  
Author(s):  
T. M. Dillon ◽  
J. N. Moum ◽  
T. K. Chereskin ◽  
D. R. Caldwell
Keyword(s):  
Momentum Balance ◽  
Zonal Momentum Balance ◽  
Zonal Momentum

scholarly journals Ocean and Atmosphere Storm Tracks: The Role of Eddy Vorticity Forcing

2007 ◽  
Vol 37 (9) ◽  
pp. 2267-2289 ◽  
Author(s):  
Richard G. Williams ◽  
Chris Wilson ◽  
Chris W. Hughes
Keyword(s):  
Storm Track ◽  
Heat Fluxes ◽  
Storm Tracks ◽  
Mean Flow ◽  
Ocean Eddies ◽  
Boundary Currents ◽  
The Mean ◽  
Circumpolar Current ◽  
The Antarctic

Abstract Signatures of eddy variability and vorticity forcing are diagnosed in the atmosphere and ocean from weather center reanalysis and altimetric data broadly covering the same period, 1992–2002. In the atmosphere, there are localized regions of eddy variability referred to as storm tracks. At the entrance of the storm track the eddies grow, providing a downgradient heat flux and accelerating the mean flow eastward. At the exit and downstream of the storm track, the eddies decay and instead provide a westward acceleration. In the ocean, there are similar regions of enhanced eddy variability along the extension of midlatitude boundary currents and the Antarctic Circumpolar Current. Within these regions of high eddy kinetic energy, there are more localized signals of high Eady growth rate and downgradient eddy heat fluxes. As in the atmosphere, there are localized regions in the Southern Ocean where ocean eddies provide statistically significant vorticity forcing, which acts to accelerate the mean flow eastward, provide torques to shift the jet, or decelerate the mean flow. These regions of significant eddy vorticity forcing are often associated with gaps in the topography, suggesting that the ocean jets are being locally steered by topography. The eddy forcing may also act to assist in the separation of boundary currents, although the diagnostics of this study suggest that this contribution is relatively small when compared with the advection of planetary vorticity by the time-mean flow.

Sign in / Sign up

Export Citation Format

Share Document