Transport variability in the Korea/Tsushima strait: Characteristics and relationship to synoptic atmospheric forcing

The characteristics of high-frequency transport variation through the Korea/Tsushima Strait and its response to atmospheric synoptic forcing are investigated by using acoustic velocity measurements and a barotropic model. The first principal mode for the current data in the high-frequency band (3-50 days) is mostly coherent to transport variation through the strait. As the dominant mode, the cross-sectional pattern of the transport variability is clarified: strong axes exist in the centers of the western and eastern channels of the strait. Seasonal change in the high-frequency variability is also elucidated: it is strong from November to January, peaks in April and September, and is weak from May to August. Both data analysis and numerical experiments clarify that the transport variation is mainly attributable to wind and pressure forcing, especially in a synoptic time band (3-9 days). The amplitude of the high-frequency variability is even stronger than that of seasonal transport variation. The lagged cross-covariance reveals a spatial pattern that causes the transport variation to be a synoptic weather system passing eastward along the mid-latitudes with a period of around 5 days. The transport response to this synoptic change is investigated through numerical experiments with idealized atmospheric forcing. The experiments reveal that about 40-50% of the total transport fluctuations in the synoptic time band are explained by the idealized forcing, with a contribution from wind stress higher than that from pressure. Sensitivity experiments on the forcing area show that the pressure-driven transport fluctuation is mainly determined by forcing over the East/Japan Sea. Additional experiments indicate that the strait transport fluctuation responds coherently to the local and remote winds of the synoptic atmospheric forcing.