The mechanics of eddy transport from one hemisphere to the other

Nathan Paldor*, Andrey Sigalov, Doron Nof

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The trajectory of a dense eddy propagating along the bottom of a meridional channel of parabolic crosssection from the southern to the northern hemisphere is described by a Hamiltonian system with two degrees of freedom. Two simplified types of motion exist in which the meridional acceleration vanishes: in midlatitudes the motion is geostrophic, poleward (equatoward) directed along the western (eastern) flank of the channel, while on the equator the motion consists of zonal oscillations along the potential-well generated by the bottom parabolic cross-section of the channel. The eddy's propagation along the equator is much faster than that in midlatitudes, which enhances its dissipation via mixing with the overlying ocean water. For motions that occur slightly off the equator the eastward segment is stable while the westward segment is unstable, so an expulsion from the equatorial regime takes place during the latter. A dense eddy that arrives near the equator along the west flank of the channel, has to cross the channel to its east flank where it can either oscillate back (westward) to the other side, or move poleward from the equator along the channel's east flank. The eddy's dissipation during the equatorial part of its trajectory is very large, and the probability of the dissipated eddy leaving the equator to either hemisphere is identical. The non-integrability of the system is manifested in the sensitive combination of the equatorial and the midlatitude regimes that renders the dynamics of the transport of dense eddies across the equator chaotic. This description explains both the sharp decrease in the amount of Antarctic bottom water mass in the immediate vicinity of the equator in the western Atlantic Ocean and the 'splitter' effect of the equator. This effect, encountered in earlier fluid dynamical numerical simulations, causes a current, and a cloud of particles, to chaotically split into two parts flowing in different hemispheres.

Original languageEnglish
Pages (from-to)2011-2025
Number of pages15
JournalQuarterly Journal of the Royal Meteorological Society
Volume129
Issue number591 PART B
DOIs
StatePublished - Apr 2003

Keywords

  • AABW transport
  • Cross-equatorial flow
  • Non-integrable Hamiltonian dynamics

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