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  • Author or Editor: D. J. Olbers x
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D. J. Olbers
and
J. Willebrand

Abstract

The level of no motion plays a central role in the classical dynamic method and the more advanced diagnostic schemes of the β-spiral (e.g., Stommel and Schott) and inverse method (Wunsch) to calculate the absolute velocity in the ocean. Following simple arguments, each velocity component should vanish on separate surfaces in the fluid and the absolute velocity vector vanishes on the intersection of these surfaces, i.e., on curves in the fluid. It has been suggested, however, that besides these simple configurations there may be surfaces in the fluid on which the velocity vector vanishes. Killworth has been a diagnostic scheme on this concept which is different from the β-spiral approach and the inverse method. In this note we examine the possible configuration of the level of no-motion in a fluid using ideal fluid theory. It is shown that stagnation surfaces in the fluid, i.e. surfaces on which the velocity vector vanishes, normally do not exist.

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D. J. Olbers
and
J. Willebrand

Abstract

No abstract available.

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S. D. Danilov
,
V. M. Gryanik
, and
D. J. Olbers

Abstract

The authors investigate the spreading stage of the deep ocean convection for a strip-shaped convective region to study the law of spreading and sensitivity of the eddy exchange efficiency parameter to the shape of the region and the background stratification. To simulate this convection process a two-layer quasigeostrophic model is used and the input of buoyancy due to surface cooling is parameterized through creation of pairs of baroclinic point vortices with opposite signs of potential vorticity (hetons) at a constant rate. It is shown that the eddy exchange efficiency parameter for lateral fluxes of potential density out of the convective region is not universal but essentially depends on the shape of the region and the relative layer thicknesses. The horizontal spreading of the potential density anomaly shows a faster than diffusive, quasi-linear dependence on time at moderate values of the surface buoyancy flux. This behavior is due to the specific dynamics of hetons and heton clusters.

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J-O. Wolff
,
E. Maier-Reimer
, and
D. J. Olbers

Abstract

The paper gives a detailed account of the dynamical balance of a wind-driven zonally unbounded flow over topography. The problem is investigated with a quasi-geostrophic β-plane channel with two layers and eddy resolution. The channel has a width of 1500 km and a zonal periodicity of 4000 km. Apart from the dimensions, the model structure is similar to the one used by McWilliams et al. The experiments with this model address the problem of the relative role of transient and standing eddies as well as bottom friction and topographic form stress in the balance of a current driven by a steady surface windstress. The response of the system is investigated for different values of the friction parameter and various locations of topographic obstacles in the bottom layer of the channel. The principal momentum balance emerging from these experiments supports the concept of Munk and Palmén for the dynamics of the Antarctic Circumpolar Current, which proposes that the momentum input by windstress is transferred to the deep ocean—where it leaves the system activity—where it leaves the system by topographic form stress. Frictional effects in the balance of the circumpolar flow may thus be of minor importance. This concept of the momentum balance is confirmed in simulations over more complex topographies. Here we have taken two differently scaled versions of the highly resolved bottom relief in the Macquarie Ridge area. The flow in these simulations is virtually frictionless in the momentum balance. The flow pattern reflects some features of the Circumpolar Current in this areas.

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