• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.17 no.4
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• pp.225-242
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• 2012

This is the first attempt to produce simultaneous surface current field from satellite altimeter data for the entire East Sea and to provide surface current information to users with formal description. It is possible to estimate surface geostrophic current field in near real-time because satellite altimeters and coastal tide gauges supply sea level data for the whole East Sea. Strength and location of the major currents and meso-scale eddies can be identified from the estimated surface geostrophic current field. The mean locations of major surface currents were explicated relative to topographic, ocean-surface and undersea features with schematic representation of surface circulation. In order to demonstrate the practical use of this surface current information, exemplary descriptions of annual, seasonal and monthly mean surface geostrophic current distributions were presented. In order to objectively classify surface circulation patterns in the East Sea, empirical orthogonal function (EOF) analysis was performed on the estimated 16-year (1993-2008) surface current data. The first mode was associated with intensification or weakening of the East Korea Warm Current (EKWC) flowing northward along the east coast of Korea and of the anti-cyclonic circulation southwest of Yamato Basin. The second mode was associated with meandering paths of the EKWC in the southern East Sea with wavelength of 300 km. The first and second modes had inter-annual variations. The East Sea surface circulation was classified as inertial boundary current pattern, Tsushima Warm Current pattern, meandering pattern, and Offshore Branch pattern by the time coefficient of the first two EOF modes.

• Proceedings of the KSRS Conference
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• v.1
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• pp.352-355
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• 2006

In this study, the seasonal and inter-annual variation of sea surface current in the Gulf of Thailand were revealed through the use of WOD temperature and salinity data and monthly sea surface dynamic heights (SSDH) from TOPEX/Poseidon and ERS-2 altimetry data during 1995-2001. The mean dynamic height and mean geostrohic current were derived from the climatological data while SSDH data gave monthly dynamic heights and their geopstrophic currents. The mean geostrophic current showed strong southward and westward flow of South China Sea water along the gulf entrance. Counterclockwise eddy in the inner gulf and the western side of the gulf entrance associated with upwelling in the area. Seasonal geostrophic currents show basin-wide counterclockwise circulation during the southwest monsoon season and clockwise circulation during the northeast monsoon season. Upwelling was enhanced during the southwest monsoon season. The circulation patterns varied seasonally and inter-annually probably due to the variation in wind regime. And finally we found that congregation, spawning, and migration routes of short-bodied mackerel conform well with coastal upwelling and surface circulation in the gulf.

• Ocean and Polar Research
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• v.23 no.2
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• pp.133-139
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• 2001

Ocean currents estimated from sea height anomalies derived from inter-calibrated TP/ERS are compared with daily mean currents measured with satellite-tracked drifters. The correlation coefficient between the geostrophic current from TP/ERS and surface current at 15 m depth from drifter tracks was found to be about 0.5. Due to the limitation of satellite ground tracks, small scale eddies less than 80 km are poorly resolved from TP/ERS. One of the interesting results of this study is that coastal currents along the eastern coast of Korea were well reproduced from sea height anomalies when the coastal currents were developed in association with eddies near the South Korean coast. The eddy kinetic energy (EKE) estimated from drifters, TP/ERS, and a numerical model are also compared. The EKE estimated from drifters was about 22 % higher than EKE calculated from TP/ERS. The pattern of low EKE level in the northern basin and high EKE level in the southern East Sea is shown in the EKE estimates derived from both the drifters and TP/ERS.

• 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.

• Ocean and Polar Research
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• v.38 no.2
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• pp.161-169
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• 2016

The interannual variability of the water masses was analyzed from the CTD data measured in the tropical northwestern Pacific from 2006 to 2014. There are two typical water masses NPTW and NPIW that reveal the interannual variability in the survey area, in addition to two other water masses; the surface water mass TSW with a large seasonal variability and the deep water mass AACDW with a constant temperature-salinity characteristic at the depths deeper than 2,000 meters. In 2012 and 2014 NPTW was the most widely extended horizontally and thicker than 100 meters vertically, which was found over the entire survey area. However, NPTW was reduced and became much narrower in 2009 than in the other years. NPIW seemed to expand southwards from the north of $21^{\circ}N$ to $15^{\circ}N$ in 2008 and in 2012, which showed the salinity minimum in 2013 (< 34.15 psu). The sea surface height estimated by Absolute Dynamic Topography (ADT) approximately along $135^{\circ}E$ section showed the high peaks (> $1.45dyn{\cdot}m$) between $16^{\circ}N$ and $18^{\circ}N$ during the periods between 2007 and 2009 and between 2012 and 2013; the former peak lasted wider and longer in latitude and time (about three times) than the latter. The vertical section of the geostrophic currents in the upper 1,000 meters shows that there was a mesoscale pattern of repeated eastward and westward flows a few times in some years (2010 and 2014), which seemed to disappear in some other years (2008 and 2012); the former was closely related to the mesoscale eddies and the latter implied the pattern with the permanent currents. The persistent eastward flow between $17^{\circ}N$ and $19^{\circ}N$ seems to be related to the Subtropical Countercurrent (STCC).

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.4
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• pp.195-204
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• 2009

In order to estimate sea surface current fields in the East Sea, we examined characteristics of mean dynamic topography (MDT) fields (or mean surface current field, MSC) generated from three different methods. This preliminary investigation evaluates the accuracy of surface currents estimated from satellite-derived sea level anomaly (SLA) data and three MDT fields in the East Sea. AVISO (Archiving, Validation and Interpretation of Satellite Oceanographic data) provides a MDT field derived from satellite observation and numerical models with $0.25^{\circ}$ horizontal resolution. Steric height field relative to 500 dbar from temperature and salinity profiles in the East Sea supplies another MDT field. Trajectory data of surface drifters (ARGOS) in the East Sea for 14 years provide another MSC field. Absolute dynamic topography (ADT) field is calculated by adding SLA to each MDT. Application of geostrophic equation to three different ADT fields yields three surface geostrophic current fields. Comparisons were made between the estimated surface currents from the three different methods and in-situ current measurements from a ship-mounted ADCP (Acoustic Doppler Current Profiler) in the southwestern East Sea in 2005. For offshore areas more than 50 km away from the land, the correlation coefficients (R) between the estimated versus the measured currents range from 0.58 to 0.73, with 17.1 to $21.7\;cm\;s^{-1}$ root mean square deviation (RMSD). For coastal ocean within 50 km from the land, however, R ranges from 0.06 to 0.46 and RMSD ranges from 15.5 to $28.0\;cm\;s^{-1}$. Results from this study reveal that a new approach in producing MDT and SLA is required to improve the accuracy of surface current estimations for the shallow costal zones of the East Sea.

• Korean Journal of Remote Sensing
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• v.26 no.2
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• pp.209-220
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• 2010

One of the most difficult tasks in measuring oceanic conditions is to produce oceanic current information. In efforts to overcome the difficulties, various attempts have been carried out to estimate the speed and direction of ocean currents by utilizing sequential satellite images. In this study, we have estimated sea surface current vectors to the south of the Korean Peninsula, based on the maximum cross-correlation method by using sequential ocean color images of SeaWiFS chlorophyll-a. Comparison of surface current vectors estimated by this method with the geostrophic current vectors estimated from satellite altimeter data and in-situ ADCP measurements are good in that current speeds are underestimated by about 15% and current directions are show differences of about $36^{\circ}$ compared with previous results. The technique of estimating current vectors based on maximum cross-correlation applied on sequential images of SeaWiFS is promising for the future application of GOCI data for the ocean studies.

• Ocean and Polar Research
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• v.26 no.2
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• pp.299-309
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• 2004

Conductivity-temperature-depth (CTD) data obtained along a meridional section in the eastern tropical Pacific in July 2003 have been analyzed to identify various water masses, and to examine the hydrographic structure and zonal geostrophic currents in the upper 1000 m. Water mass analysis shows the existence of subtropical and intermediate waters, characterized by layers of subsurface salinity maximum and minimum, originating from both hemispheres of the Pacific. Vertical section of temperature in the upper 200 m shows the typical trough-ridge structure associated with the zonal current system for most of the tropical Pacific. Water with the lowest salinity of less than 33.6 was found in the upper 30 m between $8.5^{\circ}N$ and $10.5^{\circ}N$ in a boundary zone between the North Equatorial Current and North Equatorial Countercurrent. Temporal changes in water properties observed at $10.5^{\circ}N$ over a period of 9 days suggest both the local rainfall and horizontal advection is responsible for the presence of the low-salinity water. Development of a barrier layer was also observed at $10.5^{\circ}N$. In the North Equatorial Current region a local upwelling was observed at $15^{\circ}N$, which brings high salinity and cooler subtropical water to the sea surface. A band of countercurrent occurs in the upwelling region between $13^{\circ}N$ and $15^{\circ}N$.

• Ocean and Polar Research
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• v.29 no.4
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• pp.283-295
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• 2007

We investigated the longitudinal variations in zooplankton abundances and their related physicochemical properties at nine stations located between $136^{\circ}W$ and $128^{\circ}W$ at $10.5^{\circ}N$ in the northeastern Pacific in summer 2004. Temperature, salinity, inorganic nutrients, chlorophyll-a (hereafter chl-a) and zooplankton ($>200\;{\mu}m$) were sampled within the depth from the surface to 200 m depth at $1^{\circ}$ longitude intervals. Zooplankton($>200\;{\mu}m$) samples were vertically collected at two depth intervals from surface to 200 m, consisting of surface mixed and lower layers (thermocline$\sim$200 m). Longitudinal distributional pattern of hydrological parameters (especially salinity) was physically influenced by the intensity of westward geostrophic current passage relating to the NEC (North Equatorial Current). Data from the longitudinal survey showed clear zonal distributions in the hydrological parameters(temperature, salinity and nutrients). However, spatial patterns of the chl-a concentrations and zooplankton abundances were mostly independent of the zonal distributions of hydrological parameters. The two peaks of zooplankton abundance in the surface mixed layer were characterized by different controlling factors such as bottom-up control from nutrients to zooplankton ($129^{\circ}W$) and accumulation by increment of friction force and taxonomic interrelationship ($133^{\circ}$ and $134^{\circ}W$). Divergence-related upwelling caused introduction of nutrients into surface waters leading to the increment of chl-a concentration and zooplankton abundances ($129^{\circ}W$). Increased friction force in relation to reduced flow rates of geostrophic currents caused accumulation of zooplankton drifting from eastern stations of study area($133^{\circ}$ and $134^{\circ}W$). Besides, high correlation between immature copepods and carnivorous groups such as chaetognaths and cyclopoids also possibly contributed to the enhanced total abundance of zooplankton in the surface mixed layer (p<0.05). Zooplankton community was divided into three groups (A, B, C) which consecutively included the eastern peak of zooplankton($129^{\circ}W$), the western peak($133^{\circ}$ and $134^{\circ}W$) and high nutrient but low chl-a concentration and zooplankton abundance ($136^{\circ}W$). Moreover, Group B corresponded to the westward movement of low saline waters(<33.6 psu) from 128 to $132^{\circ}W$. In summary, longitudinal distributions of zooplankton community was characterized by three different controlling factors: bottom-up control ($129^{\circ}W$), accumulation by increased friction force and relationships among zooplankton groups ($133^{\circ}$ and $134^{\circ}W$), and mismatch between hydrological parameters and zooplankton in the high nutrient low chlorophyll area ($136^{\circ}W$) during the study period.

• Fisheries and Aquatic Sciences
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• v.3 no.2
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• pp.97-110
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• 2000

To investigate characteristics of water masses and current structures around Noto Peninsula located in south-east coastal region of the East Sea, observation results of CREAMS (Circulations Research of the East Asian Marginal Seas) cruise and data report of oceanographic observation (Japan Meteorological Agency) in June, 1995 and 1996 were used. Water mass showing characteristics of Tsushima Warm Current (TWC) exists over the continental shelf. The depth is shallower than 200m and its width and thickness are 190km and 200m, respectively. Minimum level of dissolved oxygen occurred at the layers of maximum salinity. In the current structure, a noteworthy phenomenon is that the positions of the high-salinity water (more than 34.6 psu) match well with the distributions of the southwestward flow. In June of 1995 and June of 1996, a southwestward flow were separated into two parts along line C and line G. Current directions derived from the temperature and salinity match well with the distributions of the geostrophic currents in the vertical sections. The isothermal lines and the isohaline, which exist horizontally along the coastal area of the Japan, change abruptly at the frontal area of the Noto Peninsula, then turn toward the center of the East Sea. The dynamic depth anomalies centering around the region far northwest of the Noto Peninsula were relatively high, compared to those of other regions. The isopycnic surface (sigma-t, 25.8) existed near the surface in the central part of the East Sea, but, at the depth of 100m, the isopycnic surface was found in the coastal waters.