DEEP, CROSS-EQUATORIAL EDDIES

The question of how deep ocean eddies can cross the equator is address ed with the aid of analytical and numerical models. We focus on the po ssibility that deep ocean (lens-like) eddies can cross the equator via deep cross equatorial channels on the ocean floor. We first examine t he behavior of solid balls (i.e., free particles) in a meridional para bolic channel on a beta plane. Such balls are subject to similar topog raphical forcing and inertial forces that a lens is subject to, except that pressure forces and friction are absent. We examine both single isolated balls and a ''cloud'' of(noninteractive) balls. In general, t he balls' trajectories have a chaotic character; a fraction of the clo ud crosses the equator and ends up in the northern hemisphere, and a f raction is left behind. More realistic numerical experiments (with a f ully nonlinear reduced-gravity isopycnic model of the Black and Boudra type) show similar behavior. In all cases the equator acts as an ''ed dy smasher'' in the sense that it breaks the lens into at least two pa rts, one crosses the equator and ends up in the northern hemisphere, a nd the other is left behind. Here, however, the system is not chaotic. Despite the obvious differences between clouds of balls and eddies, t here is a remarkable similarity between the percentage of balls that p enetrate into the opposite hemisphere and the percentage of eddies' ma ss that ends up in the other hemisphere. This suggests that the geomet ry of the channel and the presence of the equator determine how the fl uid will be partitioned among the two hemispheres.