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This study clarifies the necessity of an extraordinary large coefficient of vertical viscosity for dynamical ocean modeling in a shallow and narrow strait with complex bathymetry. Sensitivity experiments and objective analyses imply that background momentum viscosity is on the order of 100 cm2 s−1, while tracer diffusivity estimates are on the order of 0.1 cm2 s−1. The physical interpretation of these estimates is also discussed in the last part of this paper. To obtain reliable solutions, this study introduces cyclic application of the dynamical response to each parameter to minimize the number of long-term sensitivity experiments. The recycling Green's function method yields weaker bottom friction and enhanced latent heat flux simultaneously with the increased viscosity in high-resolution modeling of the Tsushima/Korea Strait. [ABSTRACT FROM AUTHOR]

A long-term increasing trend in the transport of the Japan Sea Throughflow is observed from sea-level differences across the Tsushima Strait. Tidal gauge observations show sea level at Hakata, Japan, increasing at a higher rate than that at Busan, Korea. Numerical modeling results suggest that this increasing trend is forced by a northward shift in the Kuroshio axis. As the Kuroshio axis moves northward, sea level along the southern coast of Japan increases. The signal then propagates anticyclonically along the coast as topographic Rossby waves and Kelvin waves, raising sea level and, thus, increasing transport through the Tsushima Strait. [ABSTRACT FROM AUTHOR]

The volume transports measured at the Korea/Tsushima, Tsugaru, and Soya/La Perouse Straits remain quantitatively inconsistent. However, data assimilation models at least provide a self-consistent budget despite subtle differences among the models. This study examined the seasonal variation of the volume transport using the multiple linear regression and ridge regression of multi-model ensemble (MME) methods to estimate more accurately transport at these straits by using four different data assimilation models. The MME outperformed all of the single models by reducing uncertainties, especially the multicollinearity problem with the ridge regression. However, the regression constants turned out to be inconsistent with each other if the MME was applied separately for each strait. The MME for a connected system was thus performed to find common constants for these straits. The estimation of this MME was found to be similar to the MME result of sea level difference (SLD). The estimated mean transport (2.43 Sv) was smaller than the measurement data at the Korea/Tsushima Strait, but the calibrated transport of the Tsugaru Strait (1.63 Sv) was larger than the observed data. The MME results of transport and SLD also suggested that the standard deviation (STD) of the Korea/Tsushima Strait is larger than the STD of the observation, whereas the estimated results were almost identical to that observed for the Tsugaru and Soya/La Perouse Straits. The similarity between MME results enhances the reliability of the present MME estimation. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

River in the East China Sea (ECS), using a regional ECS model. Comparison between the results for 1996 and 1998 clearly shows that the summer monsoon winds play a significant role in spreading the freshwater discharge offshore and determining the dispersal of freshwater in the ECS. Analysis of 10-year simulation demonstrates that a northeastward freshwater transport to Jeju Island across the northwestern shelf of the ECS dominates during the summer period due to the surface Ekman flow by the southeasterly along-shore wind. Meanwhile, there is virtually no relationship between the amount of the summer discharge and the freshwater pathway toward Jeju Island. Our analysis also suggests that when the summer wind is relatively weak, another freshwater pathway toward the central ECS appears with the ambient along-shelf current between the Taiwan Strait and the Korea Strait. [ABSTRACT FROM AUTHOR]

Temporal variations in temperature and salinity observed in 2004 were investigated on a short time scale in the Tsushima Strait. The data were obtained by long-term in situ measurements at Mitsushima and Futaoi Island using an instrument equipped with a piston-type wiper to avoid biofouling. In addition, the temperature and salinity values of the surface layer obtained by a commercial ferryboat between Hakata and Busan were used to investigate their spatiotemporal variations. Temperature and salinity variations with a time scale of several days had a negative correlation in the summer. This evidence suggests that a warm and less saline water mass, which is considered to be mainly the Changjiang Diluted Water (CDW), flowed intermittently through the Tsushima Strait in summer. In late July 2004, a large low-salinity water mass was detected in the Tsushima Strait. At that time, the freshwater transport through the Tsushima Strait transiently reached about 12 × 104 m3s−1, which is estimated from observed acoustic Doppler current profiler (ADCP) data along a ferryboat line and inferred salinity profiles. This estimated value is more than double the maximum of the climatological monthly mean of the Changjiang discharge. Furthermore, salinity and surface current data obtained by high frequency ocean radar (HF radar) indicate that water properties at Mitsushima may occasionally represent part of the water flowing through the western channel via a countercurrent, although Mitsushima is geographically located in the eastern channel. [ABSTRACT FROM AUTHOR]

ADCP current data and sea level data from tide gauges and satellite altimetry were used in order to analyze long-term variation of the Tsushima Warm Current (TWC) volume transport passing through the Korea/Tsushima Strait. The annual mean transport of the TWC estimated from ADCP current measurement for about 17 years (1997–2013) is 2.64 ± 0.41 Sv (Sv = 106 m3s−1) in the Korea/Tsushima Strait, 1.53 ± 0.36 Sv (about 58% of the total transport) in the western channel, and 1.11 ± 0.14 Sv (about 42%) in the eastern channel. The TWC shows the minimum transport (1.74 Sv) in January and the maximum transport (3.10 Sv) in October, with seasonal variation of up to 1.36 Sv (51.5% of the annual mean transport). The seasonal variation of the total TWC transport in the Korea/Tsushima Strait is mainly similar to that in the western channel. The annual mean transport of the TWC and its seasonal variation in the Korea/Tsushima Strait, the western and eastern channels are all similar in three datasets (ADCP, tide gauge, satellite altimetry). The annual mean volume transport of the TWC estimated from long-term tide gauge data was 2.57 ± 0.37 Sv (total volume transport) for 44 years (1975–2018) in the Korea/Tsushima Strait, 1.51 ± 0.32 Sv in the western channel and 1.06 ± 0.14 Sv in the eastern channel. Long-term variation of the TWC transport shows a decreasing trend for 1975 to 1988, and an increasing trend from 1989 to 2018. For the latter period (1989 to 2018), monthly transport tends to increase in all months throughout the years, showing a greater increase, especially in spring and summer months. The increase of the transport in the eastern channel was about 2.8 times larger than that in the western channel. It is suggested that the increasing trend of the TWC transport since 1989 is related to the Pacific Decadal Oscillation (PDO), which has been changed to negative direction since mid-1980s. During the period when the negative PDO index is strong, the negative wind stress curl weakens in the mid-latitudes of the North Pacific, and the Kuroshio in the East China Sea also weakens. As a result, the flow is strengthened toward the Korea/Tsushima Strait, increasing the TWC transport. • Long-term variation of the TWC transport in the Korea/Tsushima Strait was studied. • The annual mean of the TWC transport was 2.57 ± 0.37 Sv for 44 years (1975–2018). • The TWC transport shows a decreasing trend for 1975–1988 and an increasing trend thereafter. • Its increase since 1989 is closely related to the PDO and weakening of the Kuroshio. [ABSTRACT FROM AUTHOR]