Journal Article

Tidal Conversion Into Vertical Normal Modes by Continental Margins

Kelly, Samuel M., Geoffroy, Gaspard, Nycander, Jonas

2025

Overview

We construct a computationally inexpensive semi‐analytical method to compute the tidal conversion into vertical modes by continental slopes and shelves, and apply it at the global scale. It relies on a vertically two‐dimensional reduced‐physics numerical model and uses the observed bottom topography, ocean stratification, and tidal currents as inputs. The method is applicable no matter how steep the slope is and it resolves the onshore and offshore baroclinic tidal energy fluxes. The output is validated with the conversion diagnosed from a global general circulation model simulation. Plain Language Summary Internal tides are waves generated by tidal currents flowing over rough bottom topography, and propagating in the ocean interior. The energy released by these waves, when they break, directly impacts the background ocean. Among others, it influences the oceanic heat and carbon distribution. Knowing where internal tides break is therefore key to better understanding our climate system. The problem of internal‐tide generation is highly nonlinear, and it is not yet solved for arbitrary topography. However, there exist a few alternatives to the exact mathematical description of the generated waves. Semi‐analytical methods based on linear wave theory represent one such alternative, and have been applied to most of the open ocean. However, linear theory fails completely at the step‐like topography of continental slopes. In this study, we compute the internal‐tide generation occurring at continental slopes, at the global scale, using a reduced‐physics model fed with observations. This conceptually simple model largely reproduces the conversion diagnosed from a full‐blown numerical model simulation. Our results confirm the substantial contribution from continental slopes to the global internal‐tide generation. Moreover, they unveil the modal partitioning of the energy flux in these regions. This is critical to predicting where the waves energy is dissipated. Key Points We construct a semi‐analytical method to compute the tidal conversion into modes 1–5 along continental margins globally The method resolves the onshore and offshore energy fluxes The results compare remarkably well with the conversion diagnosed from a realistic simulation

• Publisher: John Wiley & Sons, Inc,American Geophysical Union,Wiley
• Subject: Alternative energy sources / Analytical methods / Baroclinic flow / Bottom topography / Climate system / Continental margins / Continental slope / Dimensional analysis / Energy flux / Energy transfer / General circulation models / Internal tides / internal waves / Linear waves / Mathematical models / Numerical models / Numerical simulations / Ocean currents / Ocean, Atmosphere / oceanic waves / Oceans / Offshore / Physics / Sciences of the Universe / Simulation / Slopes / Stratification / Tidal currents / Tidal dynamics / Tidal energy / Tide prediction / Tides / topographic effects / Topography / Wave propagation / Waves