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The mechanics of eddy transport from one hemisphere to the other
Author(s) -
Paldor Nathan,
Sigalov Andrey,
Nof Doron
Publication year - 2003
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1256/qj.02.157
Subject(s) - equator , geology , middle latitudes , eddy , zonal and meridional , geophysics , geostrophic wind , southern hemisphere , northern hemisphere , climatology , atmospheric sciences , mechanics , physics , geodesy , latitude , turbulence
The trajectory of a dense eddy propagating along the bottom of a meridional channel of parabolic cross‐section 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 (equatorward) 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. Copyright © 2003 Royal Meteorological Society