Tide‐surge Interaction Intensified by the Taiwan Strait

The Taiwan Strait is a long and wide shelf‐channel where the hydrodynamics is extremely complex, being characterized by strong tides, and where storm surges frequently occur during the typhoon season. Obvious oscillations due to tide‐surge interaction were observed by tide gauges along the northern Fujian coast, the west bank of the Taiwan Strait, during Typhoon Dan (1999). Numerical experiments indicate that nonlinear bottom friction (described by the quadratic formula) is a major factor to predict these oscillations while the nonlinear advective terms and the shallow water effect have little contribution. It is found that the tide‐surge interaction in the northern portion of the Taiwan Strait is intensified by the strait. Simulations based on simplified topographies with and without the island of Taiwan show that, in the presence of the island, the channel effect strengthens tidal currents and tends to align the major axes of tidal ellipses along the channel direction. Storm‐induced currents are also strengthened by the channel. The pattern of strong tidal currents and storm‐induced currents along the channel direction enhances tide‐surge interaction via the nonlinear bottom friction, resulting in the obvious oscillations along the northern Fujian coast.