• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.4
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• pp.203-206
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• 2010

We examined five astronomical variables formulas of the two conventional harmonic prediction programs (IOS tidal package (IOS) and Task-2000 tidal package (Task2K)) in relation to hindcast of paleo-tides and -tidal currents on historical navel battlefields such as Myeongryang Naval Battle (September 16th, 1597 according to the lunar calendar). Through the comparison of the resultant values in a certain time (00:00 January 1) of each year (1801, 1800 and 1597) calculated from the two different formulas, we understood that the reason why Task2K is incapable of hindcating them in pre-19th century, Specifically, we found that the Task2K formulas directly using the Gregorian calendar date did not identify leap years in calculating astronomical variables beyond the period of 1801-2099. Therefore, the IOS's formulas, which use the day number referenced on midnight 1/1/0000, are recommended for use in hindcasting paleo-tides and -tidal currents on historical navel battles in pre-19th century.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.2
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• pp.189-197
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• 2011

As a multidisciplinary study encompassing oceanography and history, we have attempted to reanalyze the course of a historical navel battle, Myungryang Naval Battle(September 16th, 1597 according to the lunar calendar) through hindcasting the paleo-tidal currents and -tides(PTC). Firstly, we conducted harmonic analysis using 6-month current data observed at Uldolmok and 1-year elevation data provided by Korea Ocean Research and Development Institute in order to understand their characteristics and to hindcast the PTC. Observation results show that Uldolmok, ~300m wide, relatively narrow channel, is characterized by a flood-dominant mixed mainly semidiurnal tidal regime induced by relatively-strong shallow water constituents, showing closely a standing wave type of tidal current. Further, we hindcasted PTC on the day of Myungryang Naval Battle. Our results were compared and discussed with results(time and speeds of maximum(flood and ebb) currents and high and low water times) of the previous studies estimated from different methods. Lastly, we reconstruct the course of the event of Myungryang Naval Battle recorded in the Admiral Sun-Sin Yi's War Diary(Nangjung Iigi in Korean) based on our hindcasting results.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.3
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• pp.201-208
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• 2002

The characteristics of suspended sediment transport are analyzed at the estuaries which show significant shallow water tides, following the previous research for bottom sediment transport at the same estuaries. Several theories which are related with the formation and transition of turbidity maximum are reconfirmed by the numerical experiments. The experiments suggest the necessity of modeling the shallow water tide as a boundary condition, as was also suggested for the bed sediment transport at the previous research. Both the differences of transport characteristics between bed and suspended sediment and the differences between flood/ebb dominances and high/low water dominances are also examined at the Keum River and Youngsan River estuaries. In addition, the transport of bed and suspended sediments are found to have the opposite directions at the Youngsan River estuary which has extensive tidal flat, and thus shows pronounced ebb dominance, which is considered to be a main reason of keeping present bathymetry.

• Journal of Astronomy and Space Sciences
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• v.31 no.1
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• pp.41-50
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• 2014

The Earth is not perfectly spherical and its rotational axis is not fixed in space, and these geophysical and kinematic irregularities work as dominant perturbations in satellite orbit propagation. The International Earth Rotation Service (IERS) provides the Conventions as guidelines for using the Earth's model and the reference time and coordinate systems defined by the International Astronomical Union (IAU). These guidelines are directly applied to model orbital dynamics of Earth satellites. In the present work, the effects of the latest conventions released in 2010 on orbit propagation are investigated by comparison with cases of applying the previous guidelines, IERS Conventions (2003). All seven major updates are tested, i.e., for the models of the precession/nutation, the geopotential, the ocean tides, the ocean pole tides, the free core nutation, the polar motion, and the solar system ephemeris. The resultant position differences for one week of orbit propagation range from tens of meters for the geopotential model change from EGM96 to EGM2008 to a few mm for the precession/nutation model change from IAU2000 to IAU2006. The along-track differences vary secularly while the cross-track components show periodic variation. However, the radial-track position differences are very small compared with the other components in all cases. These phenomena reflect the variation of the ascending node and the argument of latitude. The reason is that the changed models tested in the current study can be regarded as small fluctuations of the geopotential model from the point of view of orbital dynamics. The ascending node and the argument of latitude are more sensitive to the geopotential than the other elements. This study contributes to understanding of the relation between the Earth's geophysical properties and orbital motion of satellites as well as satellite-based observations.

• Ocean and Polar Research
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• v.33 no.4
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• pp.409-419
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• 2011

Semi-diurnal internal tides and near-inertial waves are investigated using moored current meter measurements at four sites along the shelf break of the East China Sea during August 1987 and May-June 1988. Each mooring is equipped with four current meters spanning from near surface to near bottom. Spectral analyses of all current data reveal dominant spectra at the semi-diurnal frequency band, where the upper and lower current measurements show out-of-phase relationship between them with significant coherences. These are consistent with typical characteristics of the first-mode semi-diurnal internal tide. Strong intensification of the near-bottom baroclinic currents is observed only at one site, where the ratio of the bottom slope to the slope of the internal-wave characteristics at the semi-diurnal frequency is close to unity. An energetic near-inertial wave event is observed during the first half of May-June 1988 observation at two mooring sites. Rotary spectra reveal that the most dominant signal is clockwise rotating motion at the near-inertial frequency band. Upward phase and downward energy propagations, shown in time-depth contour plots of near-inertial bandpass filtered currents, are confirmed by cross correlations between the upper- and lower-layer current measurements. The upward-propagating phase speed is estimated to be about 0.13 cm $s^{-1}$ at both sites. Significant coherences and in-phase relationships of near-inertial currents at the same or similar depths between the two sites are observed in spite of their long distance of about 110 km.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.5
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• pp.333-343
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• 2010

In Mokpo coastal zone, the characteristics showing ebb-dominant tidal flow was confirmed by analysis of observed tide and tidal currents, Physical factors occurring ebb-dominant flow were reviewed. Influence of critical depth for drying, bottom shear stress, coastal reclamation, tidal amplitude, nonlinear tide, and eddy viscosity on the change of ebb-dominant flow was investigated by applying a two-dimensional circulation model. The simulation results for a variety of conditions showed that eddy viscosity and critical depth for drying does little or no impact on the generation of asymmetric flow. Strong bottom friction stress makes ebb-dominant flow clearly. Change of tidal flat into land swells ebb- dominant flow, and change of tidal flat into sea disappears ebb-dominant flow. Nonlinear tides play a decisive role in the generation of asymmetrical tidal flow. Non-linear tides should be included in the open boundary conditions of hydrodynamic modeling in the Mokpo coastal zone.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.4
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• pp.243-258
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• 2005

A fully-nonlinear two-dimensional dynamically interfaced nested tidal model has been developed with improved efficiency, usability, relocatability and also adopting different time steps for economizing computational times, which is based on two-dimensional tidal model of Choi(1990) with resolution of $1/15^{\circ}$ inlatitude by $1/12^{\circ}$ in longitude covering the whole Yellow and East China Seas continental shelf. To illustrate the validity and applicability of the present model, numerical model experiment was carried out for tidal distribution in the Yellow Sea and the East China Sea emphasizing the Saemangeum area with enhanced grid system. The results from comparison with observed value showed that the present model gives reasonable agreement. The present modeling system is a relocatable tide forecasting system designed to predict tides at any location within the Yellow Sea and the East China Sea continental shelf sea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.4
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• pp.151-164
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• 1998

Changes in tides and tidal currents in Chonsu Bay caused by the construction of Seosan A and B reclamation regions have been investigated using a depth-integrated two-dimensional tidal model. Three water level recorders were deployed for about one month and used for the specification of the open boundary condition. The computed currents were found to be in a good agreement with the measurements at two stations within Chonsu Bay. Comparison of the absolute velocities computed with the conditions before and after the embankment clearly shows that the reduction in tidal current amplitude is evident throughout the bay and the magnitude of the reduction increases to the north. Calculation shows that the embankment has advanced the time of drying at the northern part of the bay by about 51 minutes and has increased the exposure time by about 23 minutes. The high water time has advanced by about 1 hour, lowering the high water level by about 15 cm.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.1
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• pp.83-90
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• 2017

To understand the spatial-temporal distribution of seawater in Korea's South Sea, seawater movement and the distribution of water temperature has been analyzed using a hydrodynamic model (the Princeton Ocean Model). The directions of tidal currents were generally westward during flood tides and eastward during ebb tides. Northeastward Tsushima Warm Currents in the open sea, which is deeper than 50m were stronger than in coastal areas. Analysis of data from the hydrodynamic model showed that the water temperature in the semi-closed bay was relatively higher ($26{\sim}28^{\circ}C$) than in the open sea ($18{\sim}22^{\circ}C$). The exchange volume of semi-closed seawater was $10,331m^3/sec$ in Gwangyang Bay, $16,935m^3/sec$ in Yeosu-Gamag Bay and $13,454m^3/sec$ in Geoje-Hansan Bay. Therefore, it was shown that the lower seawater exchange volume is, the higher seawater temperature will be.

• 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.