Use of new baroclinic tide models to improve the correction of internal tides in SWOT and nadir altimeter data

   Interferometric missions such as SWOT, together with conventional nadir altimetry missions, provide unprecedented observations of sea surface height variability relevant to climate studies. However, the accurate exploitation of these measurements requires the correction of high-frequency signals associated with wind- and gravity-driven processes, among which internal tides and internal solitary waves represent a significant source of variability.  Internal tides, also referred to as baroclinic tides, are internal gravity waves that oscillate at tidal frequencies in the ocean interior and produce sea surface height signatures of a few centimeters. For the first vertical mode, internal tides typically exhibit horizontal wavelengths ranging from about 50 to 250 km, while higher modes are characterized by smaller spatial scales. As internal tides propagate, they may lose phase coherence and undergo nonlinear steepening, resulting in organized packets of internal solitary waves with typical horizontal scales of 1–15 km, which are clearly resolved and observed by the high spatial resolution of SWOT.

   Previous studies have demonstrated that global internal tide (IT) atlases are effective at correcting the stationary component of internal tide signals in altimetric observations (Carrère et al., 2021). In this study, we evaluate the performance of three recent global IT atlases—HRET22 (Zaron, 2024), ZHAO30yr (Zhao, 2025), and MIOST-IT24 (Tchilibou et al., 2025)—for the removal of stationary internal tide variability in SWOT and conventional nadir altimetry measurements.

   Our results show that these atlases reduce up to approximately 20% of sea level anomaly (SLA) variance at horizontal scales between 50 and 200 km. At the global scale, MIOST-IT24 generally outperforms HRET22, while ZHAO30yr exhibits the best performance in specific regions, notably the eastern Pacific, the Atlantic Ocean, and the northern Madagascar region.

    However, these global internal tide models have little to no impact at spatial scales below 50 km, which are primarily associated with higher vertical modes and internal solitary waves. This limitation highlights the need for the oceanographic community to develop new correction strategies and methodologies capable of addressing small-scale and nonlinear internal wave signals, including solitons, in high-resolution altimetric observations.