Mixing induced by the Atlantic equatorial wave activity in an eddy-resolving OGCM

The variability of equatorial circulation in the middepth Atlantic Ocean from an eddyresolving ocean general circulation model (OGCM) was analyzed. Four types of equatorially trapped waves were identified which dominate the variability of the circulation: an annual Rossby wave, a semiannual Rossby wave, a group of 40 to 60day short Rossby waves, and a group of 30day Yanai waves. In particular, the 40 to 60day short Rossby waves were found near the western boundary to the north of the equator, which may be related to nonlinear instability processes associated with the north Brazil current (NBC) retroflection. The waveinduced stirring and transport along the equator was investigated by calculating the trajectories of a large ensemble of particles in the middepth equatorial Atlantic Ocean from the eddyresolving, modelsimulated velocity field. The distribution of finitetime Lyapunov exponents derived from the simulated velocity at a depth of 2000 m bears a close resemblence to the observed CFC tongue, suggesting that the waveinduced chaotic stirring and transport may contribute to the formation of the observed CFC tongue in the middepth equatorial Atlantic Ocean along the equator.

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