Continental shelf waves forced by nonlinear continental shelf topography

The characteristics of continental shelf waves forced by nonlinear continental shelf topography are studied with a shallow-water model. Results show that there are two topographic Rossby waves and two inertia gravity waves. The northward propagating topographic Rossby wave couples with the inertia gravity wave into an unstable wave in the long wave band. When the continental slope is increased, the topographic Rossby wave still couples with the inertia gravity wave into an unstable wave, but the frequency decreases. In the South China Sea (SCS), the western boundary can develop an unstable wave because of topographic forcing, nonlinear conditions, and increasing amplitude. It is possible that the unstable wave develops into a vortex. In observations, the SCS has a strong western boundary current and abundant mesoscale vortice. There is a strong relationship between the emergence, disappearance, and movement of the circulation’s multi-eddy structure and the seasonal evolvement of the SCS’s circulation. This article shows a possible mechanism for the formation of vortices in the SCS.