Numerical study of internal waves generated by a seiche in a bay

Internal waves (IWs) play a critical role in ocean mixing processes and in the redistribution of energy and momentum. These waves are typically generated by initial perturbations, such as wind forcing at the surface, tidal interactions, and seiches interacting with abrupt bathymetric changes. A numerical study has demonstrated that seiches in semi-enclosed water bodies, such as bays, can generate IWs through energy dissipation at the open boundary via baroclinic wave drag, suggesting that bays may serve as potential energy sources for the ocean.

In this study, we use the MITgcm numerical model to simulate a seiche event in an idealized semicircular bay, based on the dimensions of Sebastián Vizcaíno Bay in Baja California, Mexico. We examine three stratification scenarios to evaluate the generation mechanism of IWs and their sensitivity to stratification. The scenarios include a barotropic case, a two-layer stratification, a realistic stratification, and a linear stratification. To analyze the structure and evolution of IWs, we use vertical velocity (www) profiles obtained at various oceanic locations. Additionally, we calculate the energy transfer from the seiche to the ocean by comparing the evolution of kinetic and potential energy in the ocean with that of the seiche, and assess the seiche’s decay rate under the different stratification scenarios.

Preliminary results reveal that the generated IWs have a period matching the fundamental seiche period of 3.6 hours due to geometry of the bay. Coastal trapped waves originating from the bay were also identified. For scenarios with continuous stratification, the linear profile scenario exhibited a uniform distribution of internal waves throughout the depth, attributed to the dispersion relation and the constant Brunt-Väisälä frequency.