Comparison of a global high-resolution ocean data assimilation system with SWOT observations
2025
Fouchet, Ergane | Benkiran, Mounir | Le Traon, Pierre-yves | Remy, Elisabeth
Surface Water and Ocean Topography (SWOT) high-resolution sea surface height (SSH) data extend the capabilities of nadir altimetry, enabling the detection of small ocean features, up to submesoscales. Assimilating these new measurements has great potential to enhance the accuracy of high-resolution global models but requires a detailed understanding of the data physical content to adapt the assimilation system accordingly. The Cal/Val 1-day repeat phase of the SWOT mission offers a unique opportunity to evaluate model performance in the high-frequency and high-wavenumber domain. SWOT SSH data are compared with outputs from Mercator Ocean International 1/12° global analysis and forecasting system. This comparison aims to characterize differences between the dynamics captured by SWOT and those represented in the model. Maps of SSH variability and spectral analyses are presented. Frequency spectra reveal good agreement between SWOT and the model at large scales but significant differences at higher frequencies. These differences are attributed to submesoscale signals in SWOT observations that were not captured by nadir altimeters or that are too small for the model grid resolution. The analyses also reveal coherent and non-coherent internal tide residuals in SWOT data. These residuals are quantified to improve the characterization of the representation error for future assimilation experiments. Insights from this study will inform and pave the way for effectively integrating SWOT data into operational systems.
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