TIDES
Tides are analyzed in the Korea-Tsushima Strait using measurements from the 11 ADCPs and 11 pressure gauges. These instruments were bottom moored at depths ranging from 59 to 142 m. Tide amplitudes range over 3 m along the southern line but only range about 0.7 m along the northern line. Maximum total current velocities exceed 100 cm/s in the surface layers and typically exceed 50 cm/s at mid-depths along both lines. These data are analyzed for eight tidal constituents, which are found to account for about 88% of the sea surface height variability along the southern line and 70% along the northern line. M2, S2, K1, and O1 are the dominant constituents. Their amplitudes are generally 10-20% lower than amplitudes from tide charts. M2 tidal velocities range from 17 to 25 cm/s along the line northeastof Tsushima Island, and are largest at the mooring on the western side of the Strait, nearest to Korea. Southeast of Tsushima Island, either M2 or K1 dominates the tidal contribution to the current, with tidal velocities ranging between 13 to 23 cm/s. Tidal velocities are fairly depth independent at mid-depths but exhibit varying degrees of depth dependence in the near-surface and near-bottom layers. While tidal currents are responsible for about 25% of the eddy kinetic energy in the near surface layer, they account for more than 50% of the eddy kinetic energy at mid-depths and about 70% near the bottom.
Tidal ellipse parameters are calculated at each depth level. Current amplitudes corresponding to the ellipse major axes and ellipse local inclination angles for the four main constituents (M2, S2, K1, and O1) as a function of depth are shown. For an entirely barotropic tide the constituent amplitude and inclination angle would appear as vertical lines. The M2 current velocity is dominant along the northern section while either M2 or K1 is largest along the southern section. K1 tidal velocities peak between 25-40 m along the southern section and are dominant in the surface layer towards the eastern end. M2 velocities along the northern section are larger than along the southern section. The S2 current velocity is the smallest of the four components along the southern line while either S2 or O1 velocities are smallest along the northern section. Differing degrees of bottom and surface boundary effects are evident in each of the constituents. At mid depths, varying degrees of depth dependence are evident. Inclination angles shown have been offset for plotting purposes. The angle ranges are relevant while the absolute magnitudes are not. Vertical inclination angle gradients are largest near the surface and near the bottom. These large gradients imply decreasing velocities and turning of the tidal ellipses. At mid-depths, the ellipse turning is minimal, generally less than 10 degrees. Turning is most pronounced near the bottom. Veering with depth of the diurnal tide is opposite that of the semi-diurnal tide.
Tide Amplitudes as a Function of Depth Southern Line
Tide Amplitudes as a Function of Depth Northern Line
The contribution of tidal currents to the total velocity field generally increases with depth, with some exceptions in the bottom boundary layers. Tides contribute more to the total velocity field along the northern section than along the southern section. Tides contribute the least towards the total current at S3 and S4 which usually coincide with the core of the Tsushima Current. Tides contribute the most towards the total current at the ends of the southern section (S1 and S6). Along the northern section, tidal currents are most dominant at N3 and N4, located in the regime of highly variable flow with a weak mean flow. Tidal effects are noticeably smaller in the near bottom layer at N2, where significant southward influx of bottom cold water has been observed.
Ratio - Tide MKE/Total MKE
Ratio - Tide EKE/Total EKE
Tide chart tidal amplitudes (cm) and Greenwich phases (squares) from Odamaki (1989, Journal of the Oceanographic Society of Japan, 45, 65-82) are compared with computed amplitudes and phases (asterisks) from pressure gauge moorings deployed along lines northeast (N2--N6) and southwest (S1-S6) of Tsushima Island.
Tide Amplitudes and Phases compared with
Charted Values