Towards a global coastal ocean model based on unstructured grids

We present a 1-year simulation performed by the MUSE (Multiscale Unstructured model for Simulating the Earth ocean) model. This is a global-ocean extension of the model SHYFEM-MPI (Micaletto et al., 2022), an MPI-based parallelization of the three-dimensional finite-element circulation model SHYFEM (System of HYdrodynamic Finite Element Modules). Some of the latest improvements in the global model include the implementation of the z-star vertical coordinates system, a new tidal module and the addition of river discharge.The experiment is run on an eddy-permitting global mesh with a variable resolution that ranges from 25 km at the equator to 6 km at the poles. The simulation is driven by the ERA5 atmospheric reanalysis and initialised with temperature and salinity climatological values from the World Ocean Atlas 2018. Atmospheric fluxes are computed through the ECMWF bulk formulae. The model results are compared with the structured-grid model NEMO, run on the ORCA025 grid with a comparable experimental setting. Furthermore, temperature and salinity are validated with satellite and in-situ data, while sea surface height is validated in coastal locations by means of tide gauge data. The analysis reveals an overall satisfactory representation of the studied variables, in both coastal and open ocean regions.Further configurations with coastal mesh refinement are currently under development. The scope is to assess storm surges induced by hurricane events, with the aim of quantifying the added value of having a higher resolution at coast in the global domain. This study could represent a step towards a new generation of models capable of integrating the coastal with the global scale.