Large Drifter Experiment in the Western Mediterranean Sea Reveals Dynamical Versus Noise Contributions in SWOT‐KaRIn Sea Level

Abstract The wide‐swath altimeter Surface Water and Ocean Topography (SWOT) provides unprecedented two‐dimensional sea‐level observations, whose ability to capture upper‐ocean dynamics requires assessment. The dynamically balanced signal and noise contributions in SWOT‐KaRIn Level‐3 (L3) sea level products are here originally quantified and contrasted with those from Level‐4 (L4) gridded nadir‐only products, combining sea level data, 137 trajectories from drifters deployed in the Western Mediterranean, ERA5 winds, and the framework of Demol et al. (2025, https://doi.org/10.1029/2024JC021637 ). The filtered L3‐2km product, or interestingly the unfiltered L3‐2km product with a 25 km Gaussian filter, offers the best compromise for fine‐scale studies, though residual noise still accounts for about one‐third of total variance. L4 products contain less balanced signal but are noise‐free and better suited for large‐scale analyses. SWOT KaRIn adds value mainly at scales smaller than ∼100 km and shorter than ∼10 days. This studies provides a benchmark for global sea‐level assessments.