Seasonal/spatial variations of the near-inertial oscillations in the deep water of the Japan Sea

A general description of the near-inertial oscillations in the deep water of the Japan Sea has been found by analyzing observed current data accumulated over a period of ten years. The near-inertial oscillations were dominant in the deep water, and those in the southern Japan Sea, the Tsushima current region, were more energetic than those in the northern area. Their temporal variations have an annual cycle with wintertime intensifications corresponding to the windy season over the Japan Sea. In the Yamato Basin, however, the power of the near-inertial oscillations was small during spring and large during summer, in addition to the above seasonal variations. The results of a slab model showed that the wind stress could account for part of the long periodic variations such as the annual cycle of the near-inertial oscillations in the deep water, but this is not expected to be their only source. Since the surface currents in the southern Japan Sea, especially in the Yamato Basin, vary significantly both temporally and spatially, the surface layer itself also could be responsible for the generation of the near-inertial oscillations in the deep water.