Preprints
https://doi.org/10.5194/os-2021-114
https://doi.org/10.5194/os-2021-114
 
06 Jan 2022
06 Jan 2022
Status: a revised version of this preprint is currently under review for the journal OS.

Internal tides off the Amazon shelf during two contrasted seasons: Interactions with background circulation and SSH imprints

Michel Tchilibou, Ariane Koch-Larrouy, Simon Barbot, Florent Lyard, Yves Morel, Julien Jouanno, and Rosemary Morrow Michel Tchilibou et al.
  • LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France

Abstract. The Amazon shelf break is a key region for internal tides (IT) generation. The region also shows a large seasonal variation of circulation and associated stratification. The objective of this study is to document how these variations will impact IT generation and propagation properties. A high-resolution regional model (1/36° horizontal resolution), explicitly resolving IT is analyzed to investigate their interactions with the background circulation and stratification, over two seasons: first MAMJJ (March to July), with weaker mesoscale currents, shallower and stronger pycnocline, and second ASOND (August to December) with stronger mesoscale currents, deeper and weaker pycnocline. IT are generated on the shelf break between the 100 and 1800 m isobaths, with a maximum on average at about 10 km offshore. South of 2° N, the conversion from barotropic to baroclinic tide is more efficient in MAMJJ than in ASOND. At the eight main IT generations sites, the local dissipation is higher in MAMJJ (30 %) than in ASOND (22 %). The remaining fraction propagates away from the generation sites and mainly dissipates locally every 90–120 km. The remote dissipation increases slightly during ASOND and the coherent M2 fluxes seem blocked between 4°–6° N west of 47° W. Further analysis of 25 hours mean snapshots of the baroclinic flux shows deviation and branching of the IT when interacting with strong mesoscale and stratification. We evaluated sea surface height (SSH) frequency and wavenumber spectra for subtidal (f < 1/28h−1), tidal (1/28h−1 < f < 1/11h−1) and super tidal (f > 1/11h−1) frequencies. Tidal frequencies explain most of the SSH variability for wavelengths between 300 km and 70 km. Below 70 km, the SSH is mainly incoherent and supertidal. The length scale at which the SSH becomes dominated by unbalanced IT was estimated to be around 250 km. Our results highlight the complexity of correctly predicting IT SSH in order to better observe mesoscale and submesoscale from existing and upcoming altmetrics missions, notably the Surface Water Ocean Topography (SWOT) mission.

Michel Tchilibou et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-114', Anonymous Referee #1, 16 Jan 2022
    • AC1: 'Reply on RC1', Tchilibou Michel Lionel, 15 Apr 2022
  • RC2: 'Comment on os-2021-114', Anonymous Referee #2, 31 Jan 2022
    • AC2: 'Reply on RC2', Tchilibou Michel Lionel, 15 Apr 2022

Michel Tchilibou et al.

Michel Tchilibou et al.

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Short summary
Internal tides are waves generated in the ocean interior with a sea surface height signature of a few centimeters, which makes them observable by satellite. This study, based on a numerical ocean model, highlights their variability during two contrasting seasons of stratification and circulation off the Amazon shelf. The variability of the internal tide will make it difficult to predict and to remove from the measurements of the future satellite SWOT.