Three‐dimensional numerical simulation of M₂ internal tides in the East China Sea

TLDR

The East China Sea and adjacent seas are among the world’s most important generation regions for the M 2 internal tide. The study investigates the distribution and energetics of the M 2 internal tide around the continental shelf edge in the East China Sea using a three‑dimensional numerical model. The model simulates how steep topographic slopes at the thermocline depth, where the M 2 barotropic tide is nearly normally incident, generate internal tides that then interfere to form a complex wave pattern. The simulations show that M 2 internal tides are efficiently generated over prominent ridges and shelf slopes, with a 35 GW conversion rate (≈10 % of incident surface energy) and a pattern that matches TOPEX/Poseidon observations, though about half of the generated energy is locally dissipated.

Abstract

The East China Sea and adjacent seas are one of the most significant generation regions of the M 2 internal tide in the world's oceans. In the present study, we investigate the distribution and energetics of the M 2 internal tide around the continental shelf edge in the East China Sea using a three‐dimensional numerical model. The numerical experiment shows that M 2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the Bashi/Luzon and Tokara Straits, the ridges along the Ryukyu Island chain, and the continental shelf slope in the East China Sea, the former particularly so. All of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the M 2 barotropic tide is almost normally incident. The M 2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern. It is found that the calculated pattern of the M 2 internal tide agrees well with TOPEX/Poseidon altimeter observations. The conversion rate from M 2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 GW. Roughly 10% of the energy in the M 2 surface tide incident on the prominent topographic features is converted to the M 2 internal tide, although about half of the M 2 internal tidal energy is subject to local dissipation in close proximity to the generation sites.