MODELING EQUATOR-CROSSING CURRENTS ON THE OCEAN BOTTOM

ABSTRACT. Observations unambiguously show that deep ocean currents carry a significant amount of fluid across the equator. Away from the equator in either hemisphere, these currents are relatively quiescent so that planetary vorticity dominates relative vorticity within the fluid. Thus, the po-tential vorticity of cross-equatorial flow changes sign en route. The breakdown of geostrophic balance at the equator because of the vanishing horizontal component of the Coriolis force and the fact that potential vorticity is not conserved in these flows constitute formidable challenges to modeling these cross-equatorial currents. Recent research points to friction as being crucial to the crossing process since it provides the mechanism by which potential vorticity can be altered. As well, since these flows are bottom-dwelling currents, the geometry of the bottom topography is an important factor in determining the portion of the current which successfully crosses the equator. We examine the dynamical balances within equator-crossing flows by studying a simplified model of the flow in the equato-rial region. This model retains the effects of friction and bot-tom topography. We compare the predictions of this model with the predictions of more sophisticated numerical models and with observations. It is shown that, despite the simplicity of the model, it captures certain aspects of the flow quite well