STEADY STATES AND VARIABILITY IN OCEANIC ZONAL
FLOWS
DIRK OLBERS and CHRISTOPH VOLKER
Alfred- Wegener-Institute for Polar and Marine Research
Bremerhaven, Germany
Contents
1 Introduction
2 Topographic resonance in the CdV model
3 A large scale baroclinic CdV model
3.1 QG planetary scale dynamics . . . .
3.2 The low-order model . . . . . . . . .
407
412
418
418
421
3.3 Steady states, stability and baroclinic resonance.
425
3.4 Time dependence . . . . . . . . . . . . . . . . . .
430
4 Comparison with high-resolution numerical models of zonal channel flow
432
4.1 Flow patterns .
433
4.2 Model tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
5 Conclusions
439
1 Introduction
The Antarctic Circumpolar Current (ACC) is the only oceanic flow system
of large scale bearing similarity to the atmospheric zonal circulation. There
is not only the obvious geometrical similarity - the zonal unboundedness of
a current reaching all around the earth - , there are also deeper dynamical
correspondences. Though the forcing is different, the dynamical balance
of the zonal atmospheric flow and the ACC resides substantially on the
excitation of and interaction with synoptic-scale eddies and the intricate
correlation of the large-scale pressure field with respect to the underlying
topography in shaping what is known as mountain drag in the atmospheric
system and bottom form drag (or stress) in the oceanic case.
In fact, the only sound explanation of the momentum budget of the
ACC, which has recently been confirmed by numerical experiments with
eddy resolving models, is merely a confirmation of a hypothesis which was
NATO AS! Series. Vol. ! 44
Decadal Climate Variability
Dynamics and Predictability
Edited by David L. T. Anderson and ltirgen Willebrand
© Springer-Verlag Berlin Heidelberg 1996