New Directional Wave Satellite Observations: Towards Improved Wave Forecasts and Climate Description in Southern Ocean.

In spite of continuous improvements of ocean wave models in the last decades, large errors still remain in particular under strongly forced conditions, often encountered in the Southern Ocean, where strong westerly winds generate some of the fiercest waves on Earth in almost unlimited fetch conditions. The newly launched China‐France Oceanography SATellite (CFOSAT) provides directional spectra of ocean waves for both wind seas and swells. Compared to Synthetic Aperture Radar (SAR), it can resolve shorter wavelengths in all directions, which dominate in non‐fully developed wind waves. Here, the assimilation of these CFOSAT wavenumber components is proved to bring more accurate predictions of wave growth compared to the assimilation of significant wave height alone. A notable reduction of model bias is found in the Southern Ocean, especially in the Pacific Ocean sector. Results further exhibit a downward shift of the wave age, consistent with theoretical wave growth curves. Plain Language Summary: This work focuses on the importance of using directional wave observations to improve model wave prediction in the Southern Ocean. The results indicate a significant impact on the transition from a wind‐dependent sea to a well‐developed sea. A direct consequence of this work will concern a better understanding of the wave climate in the Southern Ocean and therefore, an improvement of coupled ocean/waves/atmosphere systems. Key Points: The assimilation of directional wavenumber components in the wave model MFWAM induces a significant reduction of Significant Wave Height (SWH) bias in the Southern OceanData assimilation reveals the improvement of the energy transfer of wind waves during the wave growth phase under unlimited fetch conditions in the Pacific sector of the Southern OceanThe wave age and dominant wavenumber can significantly be corrected by assimilating directional observations of Surface Wave Investigation Measurements, compared with assimilation of SWH‐nadir only [ABSTRACT FROM AUTHOR]