• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.2
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• pp.351-373
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• 2019

The cold eddies around the Ulleung Basin in the East Sea were identified from satellite altimeter sea level data using the Winding-Angle method from 1993 to 2015. Among the cold eddies, the Dokdo Cold Eddies (DCEs), which were formed at the first meandering trough of the East Korea Warm Current (EKWC) and were pinched off to the southwest from the eastward flow, were classified and their migration patterns were analyzed. The vertical structures of water temperature, salinity, and flow velocity near the DCE center were also examined using numerical simulation and observation data provided by the Hybrid Coordinate Ocean Model and the National Institute of Fisheries Science, respectively. A total of 112 DCEs were generated for 23 years. Of these, 39 DCEs migrated westward and arrived off the east coast of Korea. The average travel distance was 250.9 km, the average lifespan was 93 days, and the average travel speed was 3.5 cm/s. The other 73 DCEs had moved to the east or had hovered around the generated location until they disappeared. At 50-100 m depth under the DCE, water temperature and salinity (T < $5^{\circ}C$, S < 34.1) were lower than those of ambient water and isotherms made a dome shape. Current faster than 10 cm/s circulates counterclockwise from the surface to 300 m depth at 38 km away from the center of DCE. After the EKWC separates from the coast, it flows eastward and starts to meander near Ulleungdo. The first trough of the meander in the east of Ulleungdo is pushed deep into the southwest and forms a cold eddy (DCE), which is shed from the meander in the south of Ulleungdo. While a DCE moves westward, it circumvents the Ulleung Warm Eddy (UWE) clockwise and follows U shape path toward the east coast of Korea. When the DCE arrives near the coast, the EKWC separates from the coast at the south of DCE and circumvents the DCE. As the DCE near the coast weakens and extinguishes about 30 days later after the arrival, the EKWC flows northward along the coast recovering its original path. The DCE steadily transports heat and salt from the north to the south, which helps to form a cold water region in the southwest of the Ulleung Basin and brings positive vorticity to change the separation latitude and path of the EKWC. Some of the DCEs moving to the west were merged into a coastal cold eddy to form a wide cold water region in the west of Ulleung Basin and to create a elongated anticlockwise circulation, which separated the UWE in the north from the EKWC in the south.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.2
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• pp.105-118
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• 2000

Anchored measurements (12.5 hr) of suspended sediment concentration and other hydrodynamic parameters were carried out at two stations located at the entrance to Hampyung Bay in summer (August 1999). Tidal variations in water temperature and salinity were in the range of 26.0-27.9$^{\circ}C$ and 30.9-31.5, respectively, indicating exchange offshore and offshore water mass. Active tidal mixing processes at the entrance appear to destroy the otherwise vertical stratification in temperature and salinity in spite of strong solar heating in summer. On the contrary, suspended sediment concentrations show a marked stratification with increasing concentrations toward bottom layer. Clastic particles in suspended sediments consist mostly of very fine to fine silt (4-16 ${\mu}$m) with a poorly-sorted value of 14.7-25.9 ${\mu}$m. However, at slack time with less turbulent energy, flocs larger than 40 ${\mu}$m are formed by cohesion and inter-collision of particles, resulting in a higher settling velocity. Strong ebb-dominated and weak flood dominated tidal currents, in the southwestern and the northeastern part, respectively, result in a seaward residual flow of -10${\sim}$-20 cm $s^{-1}$ at station H1 and a bayward residual flow less than 5.0 cm $s^{-1}$ at station H2. However, mean concentration of suspended sediments at station H1 is higher at flood (95.0-144.1 mg $1^{-1}$) than in ebb (75.8-120.9 mg $1^{-1}$). On the contrary, at the station H2, the trend is reversed with higher concentration at the ebb (84.7-158.4 mg $1^{-1}$) than that at the flood (53.0-107.9 mg $1^{-1}$). As a result, seaward net suspended sediment fluxes ($f_{s}$) are calculated to be -1.7 ${\sim}$-$15.610^{3}$ kg $m^{-2}$ $s^{-1}$ through the whole water column. However, the stations H1 and H2 show definitely different values of the flux with higher ones in the former than in the latter. Alternatively, depth-integrated net suspended sediment loads ($\c{Q}_{s}$) for one tidal cycle are also toward the offshore with ranges of 0.37${\times}$$10^{3}$ kg $m^{-1}$ and 0.21${\times}$$10^{3}$ kg $m^{-1}$, at station H1 and H2, respectively. This seaward transport of suspended sediment in summer suggests that summer-time erosion in the Hampyung muddy tidal flats is a rather exceptional phenomenon compared to the general deposition reported for many other tidal flats on the west coast of Korea.