A wave-induced stirring mechanism in the mid-depth equatorial ocean

摘要

A wave-induced stirring and transport mechanism for the mid-depth equatorial ocean is proposed and examined using both analytic linear equatorial 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 Lagrangian stirring and transport along the equator. In particular, a combination of an annual long Rossby wave and a high-frequency Yanai wave appears to be most effective in producing strong stirring in the interior equatorial region. Further investigations of stirring properties using an inverted, fully nonlinear reduced gravity shallow-water model support the results of the kinematic stirring study. By evaluating the finite-time estimates of Lyapunov exponents, we identified two regions where chaotic stirring is most active. One is the western boundary region where short Rossby waves likely play a dominant role in producing the strong chaotic stirring. The other is the equatorial waveguide where a low-frequency Rossby wave prescribes the pattern of the stirring geometry, and a high-frequency Yanai wave plays a role of stirring the fluid. The proposed stirring mechanism provides a plausible explanation of the observed chlorofluorocarbon distribution found in the mid-depth equatorial Atlantic Ocean.