• Journal of Environmental Science International
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• v.23 no.5
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• pp.801-806
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• 2014

Long-term change in sea level along the eastern coast of Korea was illustrated using four tide-gauge station (Pohang, Mukho, Sokcho, Ulleung) data, water temperature and salinity. Seasonal variation in the sea level change was dominant. The sea level change by steric height derived from water temperature and salinity was relatively lower than that measured from the tide-gauge stations. Sea level rising rate per year by steric height increased with latitude. The effect of salinity(water temperature) on the sea level change is greater in winter(in summer).

• Ocean and Polar Research
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• v.43 no.4
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• pp.219-227
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• 2021

Sea surface height (SSH) anomalies were estimated from data recorded by four pressure-recording inverted echo sounders (PIESs) in the Mindanao Current region over a duration of 2 years from December 2017 to November 2019. The steric components of SSH anomalies were derived from round-trip acoustic travel times from the sea floor to the sea surface, whereas mass-loading components were derived from bottom pressures. Temporal variabilities in the total (steric and mass-loading) SSH anomalies and the steric component are extremely similar; this result implies that the steric component plays a major role in SSH anomalies in this region. Comparisons of the PIES-derived SSH anomalies with satellite-measured SSH anomalies reveal that the former has less temporal variability. Correlation coefficients between the total SSH anomalies and satellite-measured SSH anomalies are less than 0.85, which is lower than the correlation coefficient between the steric components and satellite-measured SSH anomalies.

• Journal of the Korean earth science society
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• v.40 no.5
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• pp.487-501
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• 2019

In this study, steric height variability in the East Asian Seas (EAS) has been analyzed by using ocean reanalysis intercomparison project (ORA-IP) data. Results show that there are significant correlations between ocean reanalysis and satellite data except the phase of annual cycle and interannual signals of the Yellow Sea. Reanalysis ensemble derived from 15-different assimilation systems depicts higher correlation (0.706) than objective analysis ensemble (0.296) in the EAS. This correlation coefficient is also much higher than that of the global ocean (0.441). For the long-term variability of the thermosteric sea level during 1993-2010, a significant warming trend is found in the East/Japan Sea, while cooling trend is shown around the Kuroshio extension area. For the halosteric sea level, a dominant freshening trend is found in the EAS. However, below 300 m depth around this area, the signal-to-noise ratio of the linear trend is generally less than one, which is related to the low density of observation data.

• Proceedings of the KSRS Conference
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• 1999.11a
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• pp.140-143
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• 1999

SSH(Sea Surface Height) from TOPEX/Poseidon and SST data are analyzed to estimate characteristics of annual and inter-annual variations in the East Asian seas(110E - l80E, 20N - 50N) from November 1992 to May 1998. In EOF analysis of SSH and SST, 57% and 97% of the variance are represented by the first two modes. The first mode of SSH and SST shows strong annual variations expected for steric changes. The second mode of SSH shows a long-term variation, but that of SST shows 3 - 4month offset from annual variation. In the EOF analysis of the SSH and SST, 61% and 54% of the total variance are represented by the first three modes. The first mode represented a long-term variation, and the third mode reflected the bi-ennial variation. The first three mode were not strongly correlated with ENSO. We further apply Canonical Correlation Analysis(CCA) to find the dominant correlation patterns with ENSO.

• Journal of the Korean Chemical Society
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• v.34 no.3
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• pp.239-247
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• 1990

The gas-phase S_N2$ reactions can be classified into neutral bimolecular, solvated, and ionic reactions; the neutral bimolecular reaction proceeds via retention mechanism whereas the ionic reaction produces inversion products. In the reaction of solvated nucleophile with one solvent molecule, a six-center transition state (TS) is formed and the two processes i.e., retention and inversion, are found to compete with a favored path depending on the electronic effect of the nucleophile and substituents in the substrate and on the steric requirement. In the ionic reaction, the difference in the energy barrier between the two processes reduces to a small value when the substrate methyl group is made bulky, leaving ability of the leaving group is improved and at the same time the negative charge of the nucleophile is dispersed. When the reaction center atom in the $S_N2$ reaction is changed to a larger sized second row elements, the activation barrier decreases since the steric crowding in the penta-coordinated TS is relieved. However within the same row, the barrier was found to increase as the atomic size decreased. For the boron, B, the barrier height was the least since in addition to the relatively large atomic size compared to C and N, it forms tetra-coordinated TS so that the steric crowding becomes nearly negligible.

• Journal of Powder Materials
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• v.13 no.2 s.55
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• pp.138-143
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• 2006

In this study, the effects of the dispersants, i.e., Hypermer KD-2 and poly(l-vinyl-2-pyrrolidone) (PVP), and their concentration on the dispersion stability of Ni nanoparticles ($10nm{\sim}40nm$) in ethanol were investigated by using a visual inspection, a transmission profile (Turbiscan), and a zeta potential measurement. The transmission profiles measured by Turbiscan showed that the particle size increased over the entire height of the sample for suspensions with both the dispersants without showing any particle coalescence and sedimentation. The visual inspection also confirmed that the Ni suspensions with Hypermer KD-2 and PVP were very stable for more than a year. The zeta potential values varied from positive to negative with increasing the dispersant's concentration. The dispersion stability of the suspensions was not affected by both the dispersant's concentration and the zeta potential values. The observed suspension stability of Ni nanoparticles was attributed to the steric effect for the Hypermer KD-2 and to the bridging effect for the PVP.

• Journal of the Korean earth science society
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• v.33 no.6
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• pp.554-566
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• 2012

High-density temperature and salinity profiles from the successful international Argo project made it possible to reproduce the three-dimensional global ocean state in near-real time, which also increased much attention on the data analysis studies of global ocean. This paper reviewed several important issues on the recent data analysis studies such as systematic biases of XBT (eXpendable BathyThermograph) and Argo data, sea level budget discrepancy between steric height and satellite observed data, heat content change, and the current status of the development of objective analysis fields. This study also emphasized that it is required to carry out very cautious ocean data quality control and understand global-scale ocean variability prior to analyzing the regional-scale ocean climate change, particularly, in the East Asian marginal Seas.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.20 no.2
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• pp.102-118
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• 2015

This study summarized the results of the international ocean reanalysis intercomparison project. We introduced the characteristics of various ocean reanalysis systems and analyzed the assimilated performance on the typical eight oceanic variables (heat content, steric height, sea level, surface heat fluxes, mixed layer depth, subsurface salinity, depth of $20^{\circ}C$ isotherm, sea ice). In general, ensemble means show better estimations than those of any individual ocean reanalysis, but it depends on analyzed regions and variables. Among the eight oceanic variables, salinity and sea ice variabilities have large spreads among models. The deep sea, Southern Ocean, and coastal regions including western boundary current commonly appear as the areas with largest uncertainty between different objective analyses and assimilation models. We expect that intercomparison project for the ocean assimilation models independently operated in Korea should be processed, which allows us to join relevant international programs in the near future.

• 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.