Long-range internal tidal radiation and remote dissipation in the South Equatorial Current

Abstract Despite the internal tides are well-known at mid-latitudes due to their strong energy and long-range propagation, near the equator, internal tides are generally too weak to receive sufficient research interest. Utilizing combined numerical simulations and altimeter data, we reveal an M 2 internal tidal beam, originating from the Mussau Ridge with a weak generation of 0.51 GW, radiating much further than expected across the Caroline Basin. The joint effects of the ridge-trench-rise topography, negligible equatorial earth rotational force, South Equatorial Current refraction and a shallow and thin thermocline combined to induce this long-range propagation. Dissipation occurs locally near the source, but also remotely within the Caroline Basin due to the long-range propagation. Upper layer dissipation reaches 10 −9 W/kg, one to two orders of magnitude higher than near the seafloor, and only 21.5% of the total dissipation occurs below 1000 m. The remote dissipation presents the multilayer distribution, first decreasing downward and then increasing near the seafloor. The calculated internal tidal dissipation rates were generally consistent with fine-scale parameterizations, except where f approaches zero, where fine-scale parameterization becomes completely inapplicable. Our study highlights the importance of equatorial internal tide dissipation especially below the thermocline, which should be understood reliably and parameterized differently in ocean and climate models.