Observations of internal wave enhancements in an area of strong mesoscale variability in the southwestern East Sea (Japan Sea)

Oceanic inertio-gravity waves or internal waves are ubiquitous in the stratified, rotating ocean, and play a key role in providing a significant portion of energy to induce turbulent mixing, and redistributing energy and materials in the ocean. A subsurface moored time-series observation in the southwestern East Sea (Japan Sea) revealed that five episodic enhancements of internal waves were led by surface wind forcing and interaction processes among mesoscale circulation, near-inertial internal waves (NIWs), and semidiurnal internal tides (SDITs). In the upper 360 m, there were significant temporal variations of stratification-normalized horizontal kinetic energies (HKEs) of NIWs, SDITs, and continuum frequency waves (CFWs) between July and December 2003. The HKEs of NIWs were enhanced due to surface generation and interior propagation interacting with mesoscale strain and vorticity fields via wave capture process. High SDIT HKEs were observed between 53 to 360 m when the SDITs generated at northern slope of Korea Strait propagate northward and refract onto the mooring site due to mesoscale waveguide. The HKEs of CFWs significantly increased when and where the interactions between NIWs and mesoscale circulation and between NIWs and SDITs were onset. The important roles of mesoscale strain and vorticity on the internal wave field and wave-wave interaction processes are discussed to better account for the enhancements of NIWs, SDITs, and CFWs. This study supports significant impact of the mesoscale background fields and wave-wave interaction processes on the enhancements of internal waves.