Internal tide - eddy interactions and their energetics in a high-resolution complex GCM

Montag 19.05.2025, 11:00 → 12:00 Europe/Berlin

5-1.214 - Linke Seite – Großer, unterteilbarer Konferenzraum (GEOMAR - Standort Ostufer / GEOMAR - East Shore)

Speaker: Zoi Kourkouraidou, MPI, Hamburg

Hybrid  -  online via https://geomar.webex.com/geomar-en/j.php?MTID=mf415834ed76a742bacf01eada863885d

Meeting number: 2787 635 2083
Password: XYwu583sQtA

Abstract
The interactions of the internal tide (IT) with mesoscale eddies have not yet been sufficiently understood, although expected to play a significant role in energy dissipation due to scattering of the low mode IT. Observations are still too sparse in time and space and the existing numerical approaches, even though quite insightful, are still not able to answer where and when scattering, refraction and other relevant physical processes following such an interaction are important in a realistically simulated ocean. We use the ocean-only general circulation model ICON at very high horizontal resolution including the astronomical tidal forcing to study the effects of mesoscale eddies on the low-mode internal tide and their energetics in a realistic setup. We focus on the southeast Atlantic, where strong IT beams generated at the Walvis ridge are crossed by the Agulhas mesoscale eddies. Using a configuration with 5km horizontal resolution we propose a new modal decomposition method based on empirical orthogonal functions (EOFs) to extract the IT modes based entirely on non-linear primitive equation model without involving linear wave theory. Using this method we find that the mode 1 of the M2 IT is refracted, leading to a southward shift of its beam. The high modes of the internal tide are trapped inside and transported by the Agulhas rings, thus do not necessarily stem from scattering of the low-mode internal tides. Next, using an ICON configuration with a km-scale horizontal resolution, we study the energetics of these interactions by analysing the energy fluxes in areas with stronger compared to weaker eddy activity and find a small reduction of the M2 IT in presence of a strong eddying background. Our studies make an important step toward quantifying the wave-eddy interaction in a GCM with the results being as close as possible to the real-world interactions.