Hashed boxes : no tidal forcing Empty boxes: tidal forcing Blue: ORCA025, green: ORCA12, red: ORCA36 3 bands: o the large scales : from 1000 to 250 km ORCA12 and ORCA36 are close and ORCA025 is weaker in most of the boxes. o the mesoscales: from 250 km to the local first baroclinic Rossby radius of deformation The 3 configurations well differ: ORCA025 is not able to represent all the mesoscale ORCA12 can not represent the finest mesoscale processes. ORCA36 is able to represent all the mesoscale processes. o the sub-mesoscales: from the first baroclinic Rossby radius of deformation to 1 km ORCA025 and ORCA12 can not simulate sub-mesoscale phenomena. Only ORCA36 can simulate the largest sub-mesoscale processes and is able to produce SKE. Configuration: Horizontal grid : tripolar ORCA grid ( 12960 * 10850 points ) Vertical grid: 75 Z-levels, 1 meter at surface Domain Include Antarctic Ice Shelves (explicit resolution) Bathymetry: GEBCO 2019 (GEBCO, 2019) and Bedmachine Antarctica 2 Antarctic ice caps: Bedmachine Antarctica 2 Code: NEMO 4.2 release (including sea-ice SI3 model) Numerical settings: Non-linear free surface (Quasi-eulerian Coordinates formulation) Forcing: ECMWF bulk formulae + Atmospheric pressure gradient. Tracers transport: FCT advection scheme 4th order on horizontal and vertical + Explicite diffusion with iso-neutral operator Dynamic: Advection: flux form - 3rd order UBS + No explicit viscosity Vertical physic: Vertical mixing: k-epsilon vertical mixing (GLS) + adaptive-implicit vertical advection (Shchepetkin 2015) Impact of resolution on waves resolution: A minimum of 2 grid cell per Rossby radius to resolve a wave on a discrete grid (Hallberg, 2013) Global ¼°: eddy-permitting Global 1/12°: eddy-rich Global 1/36°: eddy resolving + able to represent a part of the sub-mesoscale activity: sub-mesoscale permitting. Tides representation in eddy permitting, eddy rich and sub- mesocale permitting global configurations based on NEMO OGCM. Clément Bricaud, Jérôme Chanut, Romain Bourdallé-Badie (Mercator Ocean International), Perrine Abjean (CLS) Contact: cbricaud@mercator-ocean.fr 1. Method: Model configurations and parametrizations 2. Hindcast set up 3. Kinetic Energy representation: spatial decomposition 6. Impact of choices for harmonical analysis on K1 module 11. Conclusion / Next step / Perspectives Abstract In the framework of the Copernicus Marine Environment Monitoring Service, Mercator Ocean International operates a global high-resolution forecasting system at the resolution of 1/12°. Resolving scales below 100 kilometers, and in particular sub mesoscale processes (1-50 km), appears to be essential to better represent the circulation in the open ocean (Chassignet, 2017), and, to improve the large-scale representations thanks to a more explicit energy transfers between finer and larger scales (Fox-Kemper Baylor, 2019). In particular, mixing plays a significant role in shaping the mean state of the ocean. Global internal tides are one of the sources of this mixing. Increasing resolution appears necessary to improve the barotropic tides solution and the baroclinic tides generation. Benefiting from the context of the European H2020 IMMERSE project, a new 1/36° global configuration (2 to 3 km resolution), based on the NEMO 4.2 OGCM, has been developed. Thanks to the resolution increase, this model can resolve the Rossby radius in almost all open oceans areas at global scale quite everywhere and to span a large part of the internal wave spectrum. A hierarchy of multi-year simulations at 1/4°, 1/12° and 1/36° resolution with/without explicit tide representation has been performed: for each resolution, after a 3-years spin up without tidal forcing, 2 twin 3-years runs have been realized: one without tidal forcing and one forced by the 5 tidal components K1, O1, S2, M2, N2. These models are driven at the surface by the 8km/1hour ECMWF IFS system. Atmospheric pressure forcing has been activated. We propose an evaluation