639 / 2024-09-18 19:07:05

Energetics and variability of semidiurnal Internal Tides on the East China Sea shelf: local generation and onshore propagation

internal tides,energy budget,seasonal variation,east china sea,Regional Ocean Modeling System (ROMS)

Internal tides (ITs) represent one of the major energy sources available for small-scale mixing in the ocean. The East China Sea (ECS) and adjacent seas has long been recognized to be one of the most significant generation regions of semidiurnal ITs in the world's ocean. Here, the seasonal variability and energetics of semidiurnal ITs at the ECS are studied using a high-resolution numerical model. The on-shelf variability and energetics is of particular interest which is far from fully understood. The ECS shelf break, particularly northeast of the Taiwan Island, are recognized to be the strong IT local generation and dissipation sites. The ITs show significant seasonal variations both at the ECS shelf and the shelf break due to the variation in stratification. The strongest ITs occur during June to September. The onshore IT energy fluxes can play an important role in shaping the on-shelf IT variability. Overall, the divergence of baroclinic energy flux accounts for 12% and 8% of the energy budget for depths of 100 – 200 m and 50 – 100 m, respectively. The onshore-propagating IT plays a more important role for the local IT dynamics between 100 – 200 m due to the strong onshore-propagating IT across the shelf break. Two intense onshore-propagating IT hotspots are identified, northeast of the Taiwan Island and northern ECS shelf break, which are induced by the strong IT generation and subcritical slopes, respectively. Furthermore, the local on-shelf IT generation is important, especially in summer and autumn, which induces the complex IT energy distribution. Strong IT generation near the Changjiang Estuary and at isolated seamounts is highlighted.