• Fisheries and Aquatic Sciences
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• v.11 no.1
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• pp.41-49
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• 2008

Internal waves and internal tides occur frequently along the eastern coast of Korea. During the spring-tide period in April 2003, the East Korean Warm Current (EKWC) flowed near the Korean East Coast Farming Forecast System (KECFFS; a moored oceanographic measurement system), creating a strong thermocline at the intermediate layer. Weakened stratification and well-mixed water appeared frequently around the KECFFS, with duration of approximately 1 day. The results suggest the following scenario. Baroclinic motion related to the internal tide generated high frequency internal waves around the thermocline. The breaking of those waves then created turbulence around the thermocline. After well-mixed water appeared, a current component with perpendicular direction to the EKWC appeared within the inertial period. The change in stratification around the KECFFS locally broke the geostrophic balance as a transient state. This local vertical mixing formed an ageostrophic current within the inertial period.

• Ocean and Polar Research
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• v.26 no.3
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• pp.515-521
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• 2004

The processes of formation and dissociation of gas hydrates were investigated by monitoring pressure and temperature variations in a pressure cell in order to understand the kinetic behavior of gas hydrate and the controlling factors fur the phase transition of gas hydrate below freezing. Gas hydrates were made kom guest gases ($CH_4,\;CO_2$, and their mixed-gas) and fine ice powder. We found that formation and dissociation speeds of gas hydrates were not controlled by temperature and pressure conditions alone. The results of this study suggested that pressure levels at the formation of mixed-gas hydrate determine the transient equilibrium pressure itself.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.5
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• pp.1259-1268
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• 2015

The sonic layer depth (SLD) variability is important for understanding the acoustic properties of the upper ocean that influence acoustic communications, acoustic tomography, and naval operations related to searching and detecting marine underwater vessels. Generally, the SLD is the acoustical equivalent of the mixed layer depth (MLD), although they are defined differently. In this study the SLD was compared with the MLD over the annual cycle in the East Sea using an available set of temperature-salinity observation profiles. For the comparison, various definitions and methods of the MLD had applied. As a result, the SLD in the East Sea is slight similar to the curvature method applied MLD, but the other MLD have severe differences with the SLD. Futhermore, a parabolic equation transmission model is used to evaluate the cutoff frequency trapped in surface duct. It follow that there is an optimum frequency for propagation at which the loss of sound is minimum.

• Ocean Science Journal
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• v.41 no.1
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• pp.31-41
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• 2006

Seasonal changes of abundance of the main phytoplankton groups of species (diatoms, dinoflagellates, chrysophytes, small flagellates and cryptophytes) and a set of environmental parameters were investigated in coastal and pre-estuarine waters of Peter the Great Bay (East/Japan Sea) in May-October of 1998 and 1999. Three periods of mass development were revealed: spring, summer and autumn blooms, with successive change of species. The conditions favourable for each group of species were determined. Driving mechanisms of the succession include nutrients transport through seasonal pycnocline by turbulent mixing, terrestrial nutrients supply by monsoon floods, nutrients supply by upwellings, and light control by the thickness of upper mixed layer. Summer succession could be explained by a simple SST-MLD diagram similar to Pingree S-kh diagram with sea surface temperature as indicator of stratification (S) and mixed layer depth as indicator of light availability (kh).

• Ocean Science Journal
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• v.40 no.2
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• pp.101-107
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• 2005

A simple analytical model is considered in an attempt to demonstrate a formation mechanism of the abyssal current in the East Sea. In this model, the abyssal currents are driven by wind through an outcrop region and flow along closed geostrophic contours. A rough estimate of the abyssal currents, arrived at by applying this model to the region of deep mixing in the East Sea, gives currents comparable to those observed, although there is an uncertainty in the surface area of the outcrop region. It seems that the spin-up of deep water by wind forcing through the region of deep winter mixing is, at least partly, an important contribution to the formation of the abyssal currents in the East Sea.

• Proceedings of the KSRS Conference
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• v.1
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• pp.21-24
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• 2006

Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the NINO3 domain ($150-90^{\circ}W$, $5^{\circ}N-5^{\circ}S$) are studied using an ocean data assimilation product that covers the period of 1993 to 2003. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed mostly by Ekman current advecting large-scale temperature anomalies though the southern boundary of the domain. Unlike many previous studies, we explicitly evaluate the subsurface processes that consist of vertical mixing and entrainment. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to temporal change in ML depth is negligible comparing to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in wind-driven upwelling and temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Ni? cooling events. When the advective tendencies are evaluated by spatially averaging the conventional local advective tendencies of temperature, the apparent effects of currents with spatial scales smaller than the domain (such as TIWs) become very important as they redistribute heat within the NINO3 domain. However, such internal redistribution of heat does not represent external processes that control the domain-averaged MLT.

• Journal of the korean society of oceanography
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• v.33 no.1-2
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• pp.1-7
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• 1998

In the western Weddell Sea, winter mixed layer is characterized by near-freezing temperature and higher salinity due to brine injection through sea-ice formation. This layer becomes Winter Water being capped by warmer and less saline Antarctic Surface Water during the sea-ice melt-ing season. In this study, Winter Water was preliminarily identified by the oxygen isotopic com-positions. The ${\delta}^{18}$O values of Winter Water show the progressively increasing trend from south to north in the study area. It presumably reflects the enhanced mixing with Antarctic Surface Water due to the extent of influence by low S'"0 value of sea-ice/glacier meltwater. Correlations between salinity and 6'"0 values of seawater can be used to more generally characterize Winter Water with a view to identification. However, the prediction on the degree of mixing from these relationships needs more detailed isotope data, although this study allows the oxygen isotopic composition of seawater as a tracer to identify the water mass.

• Ocean and Polar Research
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• v.31 no.4
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• pp.283-296
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• 2009

Oceanographic survey data were analyzed to understand the characteristics of a warm eddy observed in the Ulleung Basin in July 2005. The temperature distribution at 200 db and vertical sections provided evidence of the warm eddy in the Ulleung Basin (UWE05). Based on the 5$^{\circ}C$ isothermal line on 200 db temperature, the major axis was 160 km from southwest to northeast, and the minor axis was 80 km from southeast to northwest. The homogeneous layer in the thermocline of UWE05 had mean values of 10.40$^{\circ}C$ potential temperature, 34.35 psu salinity, and 26.37 kg/m$^3$ potential density (${\sigma}_{\theta}$) and provided evidence that UWE05 also existed during the winter of 2004-2005. A warm streamer initially flowed along the circumference of UWE05 and mixed with the upper central water. Two northward current cores were found on the western side of the measured current section at the central latitude of UWE05. One was the East Korean Warm Current (EKWC) and the other was the main stream of the western part of UWE05. Geostrophic transport of the upper layer (from the surface to the isopycnal surface of 26.9 ${\sigma}_{\theta}$) was approximately 2.5 Sv in the eastern side of UWE05. However, the measured transport was twice as large as the geostrophic transport. Mass conservation of geostrophic transport was well satisfied in the upper layer. The direct current measurements and geostrophic transport analysis showed that the EKWC meandered around UWE05.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.12 no.4
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• pp.390-399
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• 2007

In order to investigate the mixing of sea waters on the continental shelf in the northern East China Sea, Korea Ocean Research and Development Institute conducted hydrographic surveys including turbulence measurements using the R/V Eardo in August 2005 and August 2006. The turbulent kinetic energy dissipation rates based on velocity shear measurements are estimated to be $10^{-7}{\sim}10^{4}$, $10^{-7}{\sim}10^{-6}$, and $10^{-7}$ W/kg in the surface layer, bottom layer, and lower thermocline, respectively. The data sets suggest that surface layer water is being constantly mixed by winds. High dissipation rate in the lower thermocline seems to be caused by internal waves. The bottom layer with high dissipation rate also shows high turbidity, indicating the effect of tidal stirring turbulence. The vertical eddy diffusivities are $10^{-3}{\sim}10^{-2}m^2/s$ near the bottom, and these high values appear to arise from both the low stability and high turbulent mixing.

• Transactions of Materials Processing
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• v.27 no.1
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• pp.5-11
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• 2018

Direct energy deposition (DED) technique uses a laser heat source to deposit a metal layer on a substrate. Many researchers have used the DED technique to study the hardfacing of molds and dies. The aim of this study is to obtain high surface hardness and a sound bonding between the AISI M4 deposits and a substrate utilizing a mixed powder that contains M4 and AISI P21 powders. To prevent interfacial cracks between the M4 deposits and the substrate, the mixed powder is pre-deposited onto a JIS S45C substrate, before the deposition of M4 powders. Interfacial defects occurring between the deposits and substrate and changes in the microhardness of the intermediate layer were examined. Observations of the cross-sections of deposited specimens revealed that the interfacial cracks appeared in samples with one and two mixed layers regardless of the mixture ratio. However, the crack was removed by increasing the mixture ratio and the number of intermediate layers. Meanwhile, the microhardness in the mixed layer was found to decrease with increasing ratio of P21 powder in the mixture and that in the upper region of the deposited layers was approximately 800 HV, which was attributed to various alloying elements in the M4 powder.