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Internal tides off the Amazon shelf change with the seasons

Image of the Month - September 2022

Internal Tides are made from the interactions of surface or barotropic tides with ocean topography (shelf break, seamounts, etc). Those Internal Tides propagate at ocean layers interfaces and have sea surface height signature (SSH) of the order of centimeters. The Amazon shelf break is a key region for Internal Tide generation in the tropical Atlantic. Moreover, the seasonal variation of the ocean circulation and stratification in this region (along with the freshwater inputs from the Amazon and Para rivers) may impact Internal Tide generation, propagation, and dissipation.

This study based on a high-resolution ocean numerical model highlights the variability of Internal Tides off the Amazon shelf during two contrasted periods: March to July (MAMJJ, low eddies kinetic energy and shallow pycnocline) and August to December (ASOND, high eddies kinetic energy and deep pycnocline). The tidal components have been separated using harmonic analysis, while internal and barotropic tides are separated through vertical modes. On the Sea Surface Height amplitude (root means square) figure above, Internal Tides propagate more to the north during March to July (Figure a) than during August to December (Figure b). On the other hand, the SSH is more incoherent with more intense small-scale features (higher modes) during August to December (Figures c and d). These Internal Tide propagation differences emphasize that the knowledge of ocean circulation and stratification seasonal variabilities might be needed to optimally predict coherent Internal Tides.

Swot ocean data will need to be corrected from those Internal Tides to use the sea surface height information. Improvements are also expected from the Swot measurements to Internal Tide knowledge and modeling, as Topex/Poseidon measurements helped to improve the surface tides' models in its own time.

See also:

References:

  • M. Tchilibou, A. Koch-Larrouy, S. Barbot, F. Lyard, Y. Morel, J. Jouanno, and R. Morrow;, 2022: Internal tides off the Amazon shelf during two contrasted seasons: Interactions with background circulation and SSH imprints.  Ocean Science,  https://doi.org/10.5194/os-2021-114 (under revision)
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