Variability of the volume transport through the Korea/Tsushima Strait as inferred from the shipborne acoustic Doppler current profiler observations in 1997–2007

Abstract

The 10-year series of observations of currents directed along the Korea/Tsushima Strait, which were measured with an acoustic Doppler current profiler aboard a ferry boat that cruised several times a week between the Hakata (Japan) and Pusan (South Korea) ports, is analyzed. Robust estimation methods are used to separate the tidal signal from the inhomogeneous series of the current data in the problem of the harmonic analysis. The MU2, NO1, PHI1, and J1 constituents have been estimated in addition to the MSF, MF, Q1, O1, P1, K1, N2, M2, S2, and K2 tidal harmonics detected previously. The annual variations in the amplitude of the M2 fundamental harmonic have also been taken into account. The current series cleared from the tidal signal has been processed in order to analyze the spatio-temporal variability of the volume transport through the Korea Strait. The normal annual velocity of the water inflow into the Japan Sea through the Korea Strait was 2.77 × 10 6 m 3 s -1 . The ratio of the flow rates in the eastern and western zones of the strait separated by the Tsushima Islands was 2/3. Considerable seasonal variations in the dis- charge are observed in the western strait zone: the flow rate annual maximum in October is 1.75 times as high as the minimum in February. An insignificant (not more than 0.1 × 10 6 m 3 s -1 on average) southward flow can cross the eastern channel. Mesoscale vortices are generated in the lee of the Tsushima Islands when the northeastern current flows around them. The energy spectrum of the total nonseasonal flow rate through the Korea Strait has been con- structed in the frequency range of 8-500 days. The spectrum has three significant maximums near periods of 10, 19, and 64 days. It has been indicated that this spectrum flattens at low frequencies (<0.1 day -1 ) in the vicinity of the for- mation of mesoscale vortices behind the Tsushima Islands.