Internal tides off the Amazon shelf in the western tropical Atlantic: Analysis of SWOT Cal/Val Mission Data

Abstract. The Surface Water and Ocean Topography (SWOT) altimetry mission launched at the end of 2022 is an opportunity to access ocean variability at scales down to 15–30 km and to better understand high-frequency dynamic processes such as the internal tide (IT).  This study characterizes the internal tides off the Amazonian shelf in the tropical Atlantic; it is based on 2 km horizontally gridded observations along the swaths of SWOT track 20 during the calibration/validation phase (Cal/Val, 1-day orbit) from late March to early July 2023. Internal tide models for M2, S2 and N2 were first derived by harmonic analysis of the sea level anomaly (SLA), then improved by performing a principal component analysis (PCA) prior to harmonic analysis. The results compare very well with the high-resolution empirical tide (HRET) internal tide model, the reference product for internal tide corrections in altimetry observations. The coherent mode 1 and mode 2 can be distinguished in the internal tide model derived from SWOT, while the higher modes with their strong SLA signature seem mostly in the incoherent part. The PCA also gives an overview of the daily variability of the internal tide.