For the development of the earth-system model ICON, carried out at the Max-Planck Institute for Meteorology in cooperation with the German meteorological service (DWD), the ocean compartment plays a major role. It is now used to push the frontiers of simulating the climate based on first principles by resolving its major energetic motions, including those at small scales such as eddies and waves in the ocean. This new development, however, still requires substantial efforts. One such a process is internal tides that are generated as (barotropic) tides flow over topographic features such as underwater ridges and sea mounts. To ensure a realistic representation of internal tides, one needs to make sure that the model used is capable to realistically simulate the tides. A set of experiments has been carried to assess the ability of ICON-O to simulate open ocean tides.

Tides are tested in the global ocean model ICON-O in various horizontal resolutions: R2B6 (40km), R2B8 (10km), and BCT (BaseCampTelescope: a telescoping -inhomogeneous- grid ranging from 80km to 8km with a focus region in the South Atlantic).

All runs are performed with a relatively high vertical resolution (128 vertical levels) and additionally the vertical coordinate z* is used and different heights of top levels are applied.

To improve the simulated tides two new parameterizations are introduced in ICON-O. Self-Attraction and Loading (SAL) and a parameterization for Tidal-Bottom-Drag (TBD) are introduced individually and together in all 3 horizontal resolutions.

100 years of spin-up simulations with OMIP forcing and without tides have been performed for all set-ups. After the climate has spun-up reasonably, 3 more years of simulation now with tides have been performed. For the tides to spin-up, only the last year is evaluated. The raw model output (hourly sea surface elevation) and the spin-up runs are also available (see references).

One year (the last) of the ICON-O simulation with tides is analyzed by the least-square-fitting method of Foreman et al. (2009). From this harmonic analysis the harmonic constants of the eight major diurnal and semi-diurnal tidal constituents (M2, S2, N2, K2, K1, O1, P1, and Q1) are derived. Phases and amplitudes on the original ICON-O grid (XX_harmonics.nc) and a regridded regular 0.1-degree grid (XX_harmonics_r3600x1800.nc) are archived.