Internal Tides Reverse Tidal Currents Around Southern Taiwan

We present a highly unusual case in southern Taiwan where internal tides (ITs) completely reverse the barotropic currents. A 3D baroclinic model is first validated and confirms the unexpected tidal current in that area. A series of sensitivity simulations are then used to progressively reveal the exact cause. Contrary to popular belief, a large canyon in that area is not responsible for the flow reversal. Results from using a relaxation technique in the model together with an energy flux analysis indicate that the energy of the large ITs emanated from the Luzon Strait is converted to the barotropic energy near the steep slope, which generates a local circulation and reverses the tidal flow there. Observed tidal current in southern Taiwan, especially near Kaohsiung area are opposite to the prediction from most tidal models that suggest the flood currents are directed northwestward in southern Taiwan. The observation, however, always shows the opposite flow direction, with southeastward tidal flow during flood and northwestward flow during ebb. In this study, we develop a 3D model and conduct sensitivity tests to reveal the exact cause of this unusual flow feature: the internal tides propagated from Luzon strait. Unexpected tidal current near southern Taiwan is identified Using different scenario model setups, internal tide is identified as the main reason to reverse the tidal current 3D Baroclinic model setup is necessary to capture the unexpected flow feature