High-Frequency Variability: Basin-Scale Oscillations and Internal Waves/Tides

High-frequency variability captured by recent observations in the East Sea (Japan Sea) is summarized; it includes basin-scale oscillations, internal tides, near-inertial oscillations, and nonlinear internal waves. Observational and theoretical/numerical studies have been conducted on non-isostatic sea level response to atmospheric pressure forcing within the East Sea at periods of a few days to tens of days. Semidiurnal water temperature oscillations and their surface signatures are often markedly enhanced along and off the east coast of Korea due to propagation and refraction of internal tides generated at the Korea Strait shelf break; this has implications for the properties of water masses (e.g. intermediate water) and circulation (particularly off the Russian coast) in the East Sea, particularly from late summer to early winter. Research on heterogeneous and stochastic near-inertial oscillations in the open basin and coastal areas off Korea and Japan has shown a clear seasonal cycle in surface inertial motions, and interactions of near-inertial waves with mesoscale circulation, bathymetry, coastal trapped waves, and coastal/bottom boundaries. Observations of nonlinear internal waves and their packets at near-inertial and semidiurnal intervals, have suggested generation by both semidiurnal internal tides and wind-induced near-inertial waves. Investigation of high-frequency variability in the East Sea is far from closed, and the several results introduced in this chapter raise many questions rather than provided answers. A general presumption of stationary characteristics of such high-frequency variability under changing climate conditions needs to be tested; this requires long-term time series observations with high temporal sampling rates at relevant spatial resolutions.