Generation mechanisms and energetics of internal waves around an island

Shallow ridges, seamounts and islands have been known as generation site of strong baroclinic internal tides in coastal oceans. However, details of generation and propagation processes of such internal waves/tides have not been investigated well. In this study, generation processes of internal tides around islands were investigated by using numerical simulation performed by Stanford Unstructured Nonhydrostatic Terrain-Following Navier-Stokes Similator (SUNTANS). This study focuses on Izu-Oshima Island located off Sagami Bay, Japan. The barotropic tides generated strong baroclinic internal waves around the study site. The diurnal tidal frequency (~ K1) is lower than the inertial frequency (f) in the mid latitude, which results in strongly enhanced Kelvin trapped internal tides around the island. The isothermal displacement due to diurnal internal tides reached 50 m in the model. The internal wave energy generated by diurnal tides was resonated around the island and was much higher than that of semi-diurnal (~ M2) internal tides. Shallow ridges near the island enhanced non-linearity of internal waves, which induces high frequency internal waves. Such high frequency waves cannot be trapped around the island, because their frequency is higher than the inertial frequency. These high frequency waves were released from the island and propagated to the offshore, like nonlinear solitary waves. In addition, numerical results showed good consistencies with observed results taken near the island.