07 Mar 2023
 | 07 Mar 2023
Status: this preprint is open for discussion.

Regional modeling of internal tide dynamics around New Caledonia: energetics and sea surface height signature

Arne Bendinger, Sophie Cravatte, Lionel Gourdeau, Laurent Brodeau, Aurélie Albert, Michel Tchilibou, Florent Lyard, and Clément Vic

Abstract. The Southwestern Tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal tide field around the New Caledonia islands through energy budgets that quantify the internal tide generation, propagation, and dissipation. A total of 15.97 GW is converted from the barotropic to the baroclinic tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy dissipates in the near-field close to the generation sites. The remaining energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m−1 toward the open ocean, strongly dominated by mode-1. The energetic mesoscale eddy activity in the region appears to be the main source of tidal incoherence. Locally, mesoscale eddy-driven stratification changes induce variations of the conversion term. In the far-field, incoherence of the energy flux arises through the interaction of the tidal beam with the eddying background flow. The New Caledonia site represents a challenge for SWOT (Surface Water Ocean Topography) observability of meso- and submesoscale dynamics in the presence of internal tides with sea surface height signatures > 6 cm. We show that a correction of the coherent baroclinic tide may improve the observability range by shifting the transition scale between balanced and unbalanced flow in winter from 180 km to 50–80 km. In contrast, in summer observability increases only marginally due to the seasonally amplified signature of the incoherent tide at scales below 100 km.

Arne Bendinger et al.

Status: open (until 02 May 2023)

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Arne Bendinger et al.

Arne Bendinger et al.


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Short summary
New Caledonia represents a hot spot of internal tide generation. Using regional modeling, we show that the bulk of energy is converted in shallow waters and on very steep slopes. Tidal beams emerge from the generation sites despite strong energy dissipation. Tidal incoherence is linked with mesoscale eddies. The region exhibits a challenge for SWOT observability of meso-/submesoscale dynamics. Correcting the SSH for the coherent internal tide may improve observability in winter down to 50 km.