Scattering of near-inertial internal waves along the Japanese coast of the Japan Sea

摘要

The scattering of near-inertial internal waves (NIIWs) induced at the tips of landmasses was investigated by mooring observations using current meters and thermometers in the surface layer along peninsulas and an island located along the Japanese coast of the Japan Sea during the fall of 2006. Signals of NIIWs were found in alongshore currents and in temperatures recorded near the seasonal thermocline. The signals appeared after wind stress had reached a maximum, and they lasted for more than 2 days. Relatively high current energy regions due to NIIWs were localized around the northern parts of the peninsulas and island. The phase lag of the temperature fluctuations increased in the southern regions along the eastern coasts of the peninsulas and island. The generation and propagation of NIIWs were investigated by numerical experiments that used a multilayer level model with realistic topography. Model results showed that NIIWs induced by the wind struck the tips of landmasses and scattered and that NIIWs were trapped by the coast and propagated with characteristics of coastal-trapped waves (CTWs) and then rapidly attenuated. The CTWs had a distorted current structure at landmass tips because of periodic beam-like current structures from the seafloor. These signals show that CTWs radiate energy away from the shore as internal waves originating from topographical scattering, which is considered to cause the rapid attenuation of the CTWs.