Swot observations of internal tides analyzed
Internal tides, generated by the interaction of the barotropic tide with sharp bathymetric gradients, propagate along density interfaces within the ocean. They have been observed in optical and SAR imagery, monitored with difficulty and coarse resolution by nadir altimetry along satellite tracks, and simulated using ocean numerical models. The launch of Swot late 2022 now offers the opportunity to observe internal internal in two dimensions and with high precision.
A study by Tchilibou et al. [2025], based on the Swot 1-day CalVal orbit over the Amazon shelf, a key region for internal tide generation in the tropical Atlantic, aims to discriminate the main semi-diurnal tidal components (M2, S2, and N2; see Image of the Month, Sep. 2022 ) of the internal tide using harmonic and empirical orthogonal function (EOF) analyses. The results are promising, providing an unprecedented view of these components, despite relying on only three months of data. A longer Swot time series will be required to discriminate the diurnal and longer-period internal tide components more accurately. This will certainly be possible with data from Swot's 21-day repeat orbit. Incorporating Swot data into altimetry databases will certainly improve the quality of existing internal tide atlases.
Reference:
- Tchilibou, M., Carrere, L., Lyard, F., Ubelmann, C., Dibarboure, G., Zaron, E. D., and Arbic, B. K.: Internal tides off the Amazon shelf in the western tropical Atlantic: analysis of SWOT Cal/Val mission data, Ocean Sci., 21, 325–342, https://doi.org/10.5194/os-21-325-2025, 2025.
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