Observation of near-inertial internal waves in the abyssal Japan Sea

Observation with a moored Acoustic Doppler Current Profiler (ADCP) set to a very short measurement interval revealed vertical propagation of near-inertial internal waves (NIW) in the abyssal Yamato Basin in the Japan Sea. Flow and temperature measurements showed a sinusoidal variation having near-inertial period associated with NIW. From the polarization of flow vectors, vertical and horizontal wave numbers of the NIW were estimated to be 1.741 × 10^-3 m^-1 and 2.563 × 10^-4 m^-1 respectively. Phase propagation of the NIW was downward at speed of 5.34 × 10^-2 ms^-1 indicating an upward group velocity. Back-tracing of the energy ray path of NIW passing through the observation point shows that the observed NIW were the bottom-reflected waves. The bottom reflected waves were the downward-propagating NIW generated in the upper layer. An event of clockwise rotation of wind vectors was suggested as a cause of the observed NIW.