[A-CG40] Dynamics of Oceanic and Atmospheric Waves, Vortices, and Circulations

[ACG40-05] Generation of superinertial internal tides propagating along the coast: the role of topographic modes in the formation of topographically modified internal Kelvin waves

*Yuki Tanaka¹ (1.Faculty of Marine Science and Technology, Fukui Prefectural University)

Keywords:Surface–Internal Decomposition, Energy Conversion Rate, Bottom Topography, Diapycnal Mixing

Internal tides are an important energy source for diapycnal mixing in the ocean interior. It is known that the subinertial internal tides have a baroclinic vertical structure in deep areas but a more barotropic structure in shallower areas, making the conventional barotropic–baroclinic decomposition ineffective to separate internal tides from surface tides. To address this issue, Tanaka (2023) introduced a “topographic mode” which represents internal motions with a barotropic vertical structure, and proposed a new energy diagram enabling us to quantify the generation of subinertial internal tides. In this study, the applicability of this new energy diagram to superinertial internal tides is investigated by performing idealized numerical experiments in which uniform surface tides pass over a continental slope with a bump in the coastline at various inertial frequencies. The calculated results show that both the topographic and baroclinic modes are generated over the bump and propagate downstream along the coast, coupling to form a topographically modified internal Kelvin wave whose cross-sectional structure closely resembles that obtained by solving a two-dimensional eigenvalue problem for a superinertial frequency. The energy conversion rate from the surface to the topographic mode is about half of the energy conversion rate from the surface to the baroclinic mode when the tidal frequency is slightly superinertial, and maintains a non-negligible contribution even when the tidal frequency is substantially superinertial. The findings of this study indicate that the new energy diagram can be applied seamlessly across the critical latitudes and possibly provides a global distribution of the internal tide generation significantly larger than the previous estimates.