• 한국해양학회지:바다
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• 제24권2호
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• pp.318-331
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• 2019

HYCOM 재분석 자료를 이용하여 동해에서 2003년과 2014년에 장기간 지속되었던 두 개의 난수성 에디를 선정하여 각각 WE03과 WE14로 명명하고 비교 분석하였다. 두 난수성 에디가 형성되는 시기는 동한난류가 평년에 비해 북상하는 것으로 나타났으며, 이들 난수성 에디는 동한난류와 아한대전선의 상호작용을 통해 상대적으로 수심이 얕은 한국대지 해역에서 생성되었다. 겨울철 연직 혼합에 의해서 난수성 에디의 중심부는 수심 150 m까지 $13^{\circ}C$, 34.1 psu 가량의 균질한 특성을 보였다. WE03이 생성된 후 이듬해인 2004년에 대한해협 서수도를 통해 동해로 유입되는 해수의 양이 평년에 비해 많았으나 WE14가 생성된 후 이듬해인 2015년에는 대한해협 서수도를 통해 동해로 유입되는 해수의 양이 평년에 비해 많지 않았다. 이에서 대마난류가 난수성 에디에 열과 염을 공급하지만, 난수성 에디의 장기 지속에는 큰 영향을 미치지 않음을 알 수 있다. 두 난수성 에디는 울릉도 부근에서 1년 6개월 이상 유지되었는데, 두 에디의 이동경로에 있어 특별한 공통점은 보이지 않았다. 울릉분지 부근에서는 동한난류의 사행 등으로 크고 작은 에디가 계속 생성된다. 장기간 존속하는 난수성 에디는 특별한 외적 요인에 의해서 생성되는 것이 아니라, 동한난류 또는 동한난류가 사행하는 과정에서 생성된 에디와의 상호작용을 통해 생성된 것으로 보인다. 동한난류가 평년에 비해 북상했던 시기에 장기간 지속된 난수성 에디가 항상 발생하지는 않았다는 점이 위와 같은 결론을 뒷받침한다.

• Ocean and Polar Research
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• 제38권4호
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• pp.259-270
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• 2016

Sea Surface Salinity (SSS) observations from the Aquarius satellite in the East Sea show large systematic biases mainly caused by the surrounding lands and Radio Frequency Interferences (RFI) along the descending orbits on which the satellite travels from the Asian continent to the East Sea. To develop a technique for correcting the systematic biases unique to the East Sea, the least square regression between in situ observations of salinity and the reanalyzed salinities by HYCOM is first performed. Then monthly mean reanalyzed salinities fitted to the in situ salinities are compared with monthly mean Aquarius salinities to calculate mean biases in $1^{\circ}{\times}1^{\circ}$ boxes. Mean biases in winter (December-March) are found to be considerably larger than those in other seasons possibly caused by the inadequate correction of surface roughness in the sea surrounded by the land, and thus the mean bias corrections are performed using two bias tables. Large negative biases are found in the area near the coast of Japan and in the areas with islands. In the northern East Sea, data sets using the ascending orbit only (SCIA) are chosen for correction because of large RFI errors on the descending orbit (SCID). Resulting mean biases between the reanalysis salinities fitted to in situ observations and the bias corrected Aquarius salinities are less than 0.2 psu in all areas. The corrected mean salinity distributions in March and September demonstrate marked improvements when compared with mean salinities from the World Ocean Atlas (WOA [2005-2012]). In September, salinity distributions based on the corrected Aquarius and on the WOA (2005-2012) show similar distributions of Changjiang Diluted Water (CDW) in the East Sea.

• 대한원격탐사학회지
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• 제39권4호
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• pp.441-458
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• 2023

Tropical cyclones frequently occur in the Southwest Pacific Ocean and are considered one of the driving forces for coastal alterations. Therefore, this study investigates the frequency and intensity of tropical cyclonesfrom 2000 to 2021 and their influence on the surface winds and wave conditions around the atoll nation Tuvalu. Cyclone best-track and ERA5 single-level reanalysis data are utilized to analyze the condition of the surface winds, significant wave heights, mean wave direction, and mean wave period. Additionally, the scatterometer-derived wind information was employed to compare wind conditions with the ERA5 data. On average, nine cyclones per year originated here, and the frequency increased to 11 cyclones during the last three years while the intensity decreased by 25 m/s (maximum sustained wind speed). Besides, a total of 14 cyclones were observed around Tuvalu during the period from 2015 to 2021, which showed an increase of 3 cyclones compared to the preceding period of 2001 to 2007. During cyclones, the significant wave height reached the highest 4.8 m near Tuvalu, and the waves propagated in the east-southeast direction during most of the cyclone events (52%). In addition, prolonged swells with a mean wave period of 7 to 11 seconds were generated in the vicinity of Tuvalu, for which coastal alteration can occur. After this preliminary analysis, it was found that the waves generated by cyclones have a crucial impact in altering the coastal area of Tuvalu. In the future, remotely sensed high-resolution satellite data with this wave information will be used to find out the degree of alterations that happened in the coastal area of Tuvalu before and after the cyclone events.

• 한국해안·해양공학회논문집
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• 제29권3호
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• pp.129-138
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• 2017

연안의 파랑환경은 해안지형의 변화, 해양생물의 서식조건, 해양구조물의 설계 등에 직접적인 영향을 미치는 매우 중요한 인자이다. 최근 기후변화로 인한 파랑환경의 변화도 예상되고 있는 상황에서, 가용한 자료를 이용한 파랑환경의 추세분석이 요구된다. 본 연구에서는 한국 연안 6개 지점(덕적도, 외연도, 칠발도, 마라도, 포항, 울릉도) 평상파랑의 부이관측 자료를 이용하여 장기 변화양상을 분석하였다. 먼저, 국내 기상청 해양기상부이 관측 자료의 이상치를 제거하기 위해 Rosner 방법을 사용하였으며, 이를 ECMWF 재해석 자료와 피어슨 상관분석을 수행하였다. 그 결과, 해양기상부이와 ECMWF 자료간의 상관성은 0.849~0.938로 나타났다. 한편, 맨-캔달 검정법을 이용하여 평상파랑의 장기변동 양상을 검토하였으며 그 결과, 덕적도, 외연도, 칠발도 지점은 변동이 없는 것으로 나타났지만, 마라도, 포항, 울릉도 지점은 증가하는 경향을 보였다.

• Selected Papers of The Society of Naval Architects of Korea
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• 제2권1호
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• pp.18-28
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• 1994

In the vibration analysis of submerged or floating bodies such as ships and offshore structures, the coupled system between fluid and structure should be considered using the compatibility conditions on the wetted surface. It is well known that the hydroelastic vibration analysis of structures in contact with fluid can be done by applying the finite element method(FEM) to structures and the boundary element method(BEM) to the fluid domain. However, such an approach is impractical due to the characteristics of the fully coupled added mass matrix of fluid on the entire wetted surface. To overcome this difficulty, an efficient approach based on a reanalysis scheme is proposed in this paper. The proposed method can be applied for cases of higher local modes and beam-like modes for which three-dimensional reduction factors are not known. The three dimensional reduction factors are not needled and thus the restrictions can be removed in the analyses of non-beam like modes or local vibration modes by considering fluid-structure interaction. The validity and calculation efficiency of the proposed method are proved through numerical examples.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.418-421
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• 2007

Using gridded wind-stress products constructed by satellite scatterometers (ERS-1, 2 and QSCAT) data and those by numerical weather prediction(NWP) model(NCEP-reanalysis), we estimate wind-driven transports of the North Pacific subtropical gyre, and compare them in the central portion of the gyre (around 300 N) with geostrophic transports calculated from historical hydrographic data (World Ocean Database 2005). Even if there are some discrepancies between the wind-driven transports by the QSCAT and NCEP products, they are both in good agreement with the geostrophic transports within reasonable errors, except for the regional difference in the eastern part of the zone. The difference in the eastern part is characterized by an anticyclonic deviation of the geostrophic transport resulting from an anti-cyclonic anomalous flow in the surface layer, suggesting that it is related to the Eastern Gyral produced by the thermohaline process associated with the formation of the Eastern Subtropical Mode Water. We also examine the consistency of the Sverdrup transports estimated from these products by comparing them with the transports of the western boundary current, namely the Kuroshio regions, in previous studies. The net southward transport, based on the sum of the Sverdrup transports by QSCAT and NCEP products and the thermohaline transport, agrees well with the net northward transport of the western boundary current, namely the Kuroshio transport. From these results, it is concluded that the Sverdrup balance can hold in the North Pacific subtropical gyre.

• 대기
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• 제21권2호
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• pp.143-149
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• 2011

A new multi-timescale analysis method, Ensemble Empirical Mode Decomposition (EEMD), is used to diagnose the variation of the MJO activity determined by 850hPa and 200hPa zonal winds from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis data for the 56-yr period from 1950 to 2005. The results show that MJO activity can be decomposed into 9 quasi-periodic oscillations and a trend. With each level of contribution of the quasi-periodic oscillation discussed, the bi-seasonal oscillation, the interannual oscillation and the trend of the MJO activity are the most prominent features. The trend increases almost linearly, so that prior to around 1978 the activity of the MJO is lower than that during the latter part. This may be related to the tropical sea surface temperature(SST). It is speculated that the interdecadal change in the MJO activity appeared in around 1978 is related to the warmer SST in the equatorial warm pool, especially over the Indian Ocean.

• 한국지구과학회지
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• 제28권5호
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• pp.613-619
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• 2007

Mesoscale low is often observed over the downstream region of the East Sea (or, northwest coast off the Japan Islands) during East-Asia winter monsoon. The low system causes a heavy snowfall at the region. A series of numerical experiments were conducted with the aid of a regional model (MM5 ver. 3.5) to examine the formation mechanism of the mesoscale low. The following results were obtained: 1) A well-developed mesoscale low was simulated by the regional model under real topography, NCEP reanalysis, and OISST; 2) The mesoscale low was simulated under a zonally averaged SST without topography. This implies that the meridional gradient of SST is the main factor in the formation of a mesoscale low; 3) A thermal contrast ($>10^{\circ}C$) of land-sea and topography-induced disturbance served as the second important factor for the formation; 4) Paektu Mountain caused the surface wind to decelerate downstream, which created a more favorable environment for thermodynamic modification than that was found in a flat topography; and 5) The types of cumulus parameterizations did not affect the development of the mesoscale low.

• Journal of Astronomy and Space Sciences
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• 제33권4호
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• pp.305-311
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• 2016

The spatial size and variation of Arctic sea ice play an important role in Earth's climate system. These are affected by conditions in the polar atmosphere and Arctic sea temperatures. The Arctic sea ice concentration is calculated from brightness temperature data derived from the Defense Meteorological Satellite program (DMSP) F13 Special Sensor Microwave/Imagers (SSMI) and the DMSP F17 Special Sensor Microwave Imager/Sounder (SSMIS) sensors. Many previous studies point to significant reductions in sea ice and their causes. We investigated the variability of Arctic sea ice using the daily sea ice concentration data from passive microwave observations to identify the sea ice melting regions near the Arctic polar ice cap. We discovered the abnormal melting of the Arctic sea ice near the North Pole during the summer and the winter. This phenomenon is hard to explain only surface air temperature or solar heating as suggested by recent studies. We propose a hypothesis explaining this phenomenon. The heat from the deep sea in Arctic Ocean ridges and/or the hydrothermal vents might be contributing to the melting of Arctic sea ice. This hypothesis could be verified by the observation of warm water column structure below the melting or thinning arctic sea ice through the project such as Coriolis dataset for reanalysis (CORA).

• 한국해안·해양공학회논문집
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• 제30권5호
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• pp.223-233
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• 2018

본 연구에서는 동해안의 너울성 고파랑 예측하기 위해 기상청 현업 예보 바람자료를 입력장으로 하여 파랑수치모델(SWAN)을 수립 및 최적화하고 동해안 동계 파랑의 예측 재현도를 평가하였다. 파랑 모델은 연안역에서의 파랑 변형을 모의하기 위해 네스팅 기법을 적용하였으며, 백파 에너지 소산항을 개선하여 너울성 파랑을 모의하였다. 수치실험을 위한 입력 바람장으로는 기상청 현업 기상예보모델인 RDAPS 및 LDAPS 자료를 사용하였다. 모의된 파랑에 대한 정확도 비교 평가를 위해 ECMWF 재분석 바람자료와 KIOST 운용해양시스템의 WRF 예측 바람자료를 이용한 파랑모델링 및 기상청 현업 파랑예보모델 결과와 연안 및 외해 4개 관측정점의 파랑 관측자료를 이용하였다. 기상청 현업 기상예보모델을 입력바람장으로 이용한 경우 연안에서는 유의파고, 첨두주기 및 평균 파향이 모두 가장 낮은 RMSE와 가장 높은 상관계수를 가졌으며, 외해에서는 모든 수치실험 결과가 관측자료와 전반적으로 잘 일치하였다. 백파항을 수정한 SWAN 모델과 기상청 현업 기상예보모델을 사용할 경우 급격하게 발생하는 고파랑 재현은 개선이 필요하지만 비교적 겨울철 폭풍파를 잘 재현하고 있다.