Persistent presence of small vertical scale velocity features during three-dimensional equilibration of equatorial inertial instability

Small vertical scale velocity features (SVSs) are ubiquitous in the upper equatorial ocean but their lifecycle and role in the large scale dynamics are only beginning to be understood. In this article, we study the development of SVSs generated through inertial instability of a prototypical equatorial zonal flow with a uniform meridional shear, U(y) = Λy. While previous studies employ a zonally symmetric setting, in which the flow is constrained to remain invariant in the streamwise direction throughout its evolution, here we use a fully three-dimensional framework. We choose a setting, in which the fastest growing linear modes are zonally symmetric and the initial perturbation is almost zonally symmetric, so that the flow remains nearly two-dimensional until the symmetric instability is fully neutralized. The secondary instabilities of the modified zonal mean flow favor zonally nonsymmetric modes, which leads to three-dimensionalization of the flow. It has been previously conjectured in the literature th...