A WAVE-INDUCED STIRRING MECHANISM IN THE MID-DEPTH EQUATORIAL OCEAN

A wave-induced stirring and transport mechanism for the mid-depth equa torial ocean is proposed and examined using both analytic linear equat orial wave solutions and a fully nonlinear reduced-gravity model. The study of kinematic stirring using the linear solutions suggests that a superimposition of a few simple equatorial waves can lead to strong L agrangian stirring and transport along the equator. In particular, a c ombination of an annual long Rossby wave and a high-frequency Yanai wa ve appears to be most effective in producing strong stirring in the in terior equatorial region. Further investigations of stirring propertie s using an inverted, fully nonlinear reduced gravity shallow-water mod el support the results of the kinematic stirring study. By evaluating the finite-time estimates of Lyapunov exponents, we identified two reg ions where chaotic stirring is most active. One is the western boundar y region where short Rossby waves likely play a dominant role in produ cing the strong chaotic stirring. The other is the equatorial waveguid e where a low-frequency Rossby wave prescribes the pattern of the stir ring geometry, and a high-frequency Yanai wave plays a role of stirrin g the fluid. The proposed stirring mechanism provides a plausible expl anation of the observed chlorofluorocarbon distribution found in the m id-depth equatorial Atlantic Ocean.