**5. Conclusions**

Two major conclusions emerge from these tests. First, the significant improvement on the wave model set-up that was used in the IBI operations in December 2019 (IBI-CO), activating current forcing (IBI-CU), data assimilation (IBI-DA), or both (IBI-OP), with the major upgrade in the performances, including data assimilation, with the scatter error indicator decreasing by more than 1% (Table 5). Second, the importance of having realistic high-quality forcings fields. In particular, the use of unrealistic currents inputs may spoil the wave model performance (Figure 8).

The research performed, combining information from different wave model solutions and several observational data sources, benefited the IBI-MFC operational wave forecast service, supporting the decision-making process, related to their latest major operational upgrade (occurred in the Copernicus Marine Operational Release March 2020). The extensive assessment performed with the IBI-DA and IBI-CU run, presented here, was useful to demonstrate, for each proposed IBI model set-up novelty, the significance of the associated improvements (in terms of IBI wave forecasting local added value). After verifying the impacts that these two proposed novelties have on the IBI wave solution (and always using, as a referential solution, the IBI wave model configuration in operations), a new IBI wave configuration (combining both the data assimilation and the current–wave coupling) were prepared to be transitioned into operations.

The significant improvement achieved by this IBI-OP configuration, with respect to the control one (IBI-CO, the IBI set-up currently in operations), in terms of wave solution over the IBI area, throughout the year 2018, supports the IBI-MFC decision to use this set-up for operational purposes, to be implemented in the IBI Wave, operational from March 2020. Furthermore, similar performance metrics were achieved by the systems in operations (see information from a 2-year validation in the Quality Information Document of the Copernicus Marine IBI wave product, Toledano et al. 2021 [31]). Finally, note that this research was useful not only to evolve the IBI-MFC operational wave forecast service, but also has been helpful to open new working lines prioritized in the Copernicus Marine service roadmap:

• Currently, the IBI-MFC is in the process of enhancing the coupling, in both directions, between waves and ocean dynamics. In the December 2020 release, the upgraded IBI wave system included improved computations of coupling parameters, such as the surface stress, and wave-breaking-induced turbulence in the ocean mixed layer. These parameters are used to drive a coupling run with the IBI MFC ocean forecast

run, based on a NEMO model application. The sensitivity coupling tests of using the Stokes–Coriolis forcing, the sea-state-dependent stress momentum fluxes and including wave-breaking energy flux in the vertical mixing, are all validated and the impact on improving the forecast is addressed by [8,53,54].

• With respect to data assimilation, directional wave spectra data assimilation based on the optimal interpolation method, applied to mean wave parameters (total energy and wave number components) of each wave train composing the wave spectrum [55], will be implemented, in order to increase the impact of assimilation [7]. Likewise, assimilation of wave data from swath altimetry is expected to be tested in the future.

**Author Contributions:** Conceptualization, M.G.S., L.A., C.T. and M.G.; methodology, C.T. and M.G.; software, C.T., M.G., A.D. and P.L.; validation, C.T., M.G., P.L. and A.D.; formal analysis, C.T., M.G., L.A. and M.G.S.; investigation, C.T. and M.G.; data curation, C.T., M.G., P.L. and A.D.; writing—original draft preparation, C.T., M.G., M.G.S. and L.A.; supervision, L.A. and M.G.S.; project administration, M.G.S. and L.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded in the framework of the E.U. Copernicus Marine Service for the IBI region (CMEMS Contract No. 100-IBI-OPER-CMEMS and Copernicus-2 Marine service contract 21002L6-COP-MFC IBI-5600).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The Copernicus Regional IBI-MFC Wave solution can be downloaded at Copernicus Marine Environmental Monitoring Service (CMEMS) (http://marine.copernicus.eu/, accessed on 18 January 2022).

**Acknowledgments:** This study has been conducted using E.U. Copernicus Marine Service Information. Specifically, from their in-situ TAC Product (INISITU\_IBI\_NRT\_OBSERVATIONS\_013\_033) and CMEMS L3 wave altimetric product (WAVE\_GLO\_WAV\_l3\_SWH\_NTRT\_OBSERVATIONS\_014\_001). Likewise, satellite observations from the HY2A mission, provided by the CNES, have been used.

**Conflicts of Interest:** The authors declare no conflict of interest.
