SWOT Sea Surface Height Disentangled in an Internal Tide Hotspot

The Surface Water and Ocean Topography (SWOT) mission has revealed high-frequency sea surface height anomaly (SSHA) variability associated with internal gravity waves (IGWs), yet direct comparison with in situ observations remains limited. We analyze a mooring array beneath SWOT Cal/Val swaths south of New Caledonia in the southwestern tropical Pacific, characterized by energetic internal tides (ITs). SWOT measurements agree closely with mooring-derived SSHA, showing three times more variance than conventional altimetry. This excess variance is driven by semidiurnal ITs with amplitudes of 10 cm, confirmed by moorings and captured by SWOT with centimeter-level accuracy, enabling improved IT characterization. SWOT-derived ITs imply that empirical IT atlases, routinely used to correct SWOT, inaccurately represent ITs. This introduces large biases in surface current velocities, exceeding 15 cm/s (80%) in regions of IT activity, emphasizing the need for improved methods to separate wave-like and balanced motions.