• Title/Summary/Keyword: 경험적 직교 함수

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A study on the influence of the China Coastal Waters nearby Jeju Island Using Satellite Data (위성 자료를 이용한 제주도 주변해역의 중국대륙연안수 영향에 관한 연구)

  • Cho Han-Keun;Yoon Hong-Joo
    • Proceedings of the KSRS Conference
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    • 2006.03a
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    • pp.91-94
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    • 2006
  • China Coastal Waters (CCW) usually appears in the seas surrounding Jeju Island annually(June to October) and is very pronounced in August. Generally, low-salinity water appears to the western seas of Jeiu Island from June through October and gradually propagates to the eastern seas, where CCW meets the Tsushima Current. Empirical orthogonal function (EOF) analysis of SLAs and SSTs indicated that the valiance in SLAs and SSTs was 95.05%(the first mode to third mode) and 98.09%(the first mode), respectively The PSD of the western waters for the first mode of EOF analysis of SLAs was stronger than that of the eastern waters because of the influence of CCW. The PSD for the EOF analysis of SSTs was similar in all areas (the Yangtze Estuary and the seas to the west and east of Jeju Island), with a period of approximately 260 days.

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Interannual Variability of Sea Water Temperatures in the Southern Waters of the Korean East Sea (한국 동남해역의 장주기 수온변동)

  • Ro, Young Jae
    • 한국해양학회지
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    • v.24 no.1
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    • pp.1-14
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    • 1989
  • This study analyzes the interannual periodicity by using the statistical techniques of probability, spectral analysis, empirical orthogonal function analysis (EOF), and coherency analysis. The data base for this study is the time series of 1971-1985 temperature, salinity in the southern waters of the East Sea, 1960-1986 mean sea level at Pusan and Izuhara, and 1960-1986 sea level atmospheric pressure at Pusan. The appearances of anomalous temperatures higher and lower than 15-year mean monthly average with one standard deviation are about 30% of total data. The significant interannual period for temperature, salinity and sea level fluctuation is 36.6, and 23.3 months. The empirical orthogonal function analyses show that the 1st mode of the EOFs is responsible for more than 90% of total variance of the surface temperature variations, while in near-bottom waters, the relative importance of the higher EOF modes is much greater explaining more than 30% of total variance. The coherency between normalized temperatures and salinities is significant at the interannual period of 36.6 and 21.3 months.

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Analysis of Temporal and Spatial Variability of Generated 2D Soil Moisture Data (우리나라 2차원 토양수분 자료의 생산과 시.공간 변화도 분석)

  • Kim, Gwang-Seob;Kim, Jong-Pil
    • Proceedings of the Korea Water Resources Association Conference
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    • 2006.05a
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    • pp.674-677
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    • 2006
  • 토양수분은 토양입자나 공극에 포함되어 있는 물을 의미하는 것으로서 여러 수문현상을 연계하는 주요변수이며, 올바른 물순환 체계를 이해하기 위해서는 토양수분에 대한 활발한 관측과 연구가 수반되어야 한다. 하지만, 우리나라의 토양수분 자료는 지상관측 자료로서 관측기간이 짧고 결측치가 많아 장기 추세나 공간변화도를 분석하기엔 미흡할 뿐만 아니라 2차원 토양수분 자료는 보유하고 있지 않은 실정이다. 따라서, 본 연구에서는 이를 보완하기 위해 우리나라와 위도가 비슷한 지역인 미국 Illinois 지역의 토양수분자료와 정규식생지수의 상관관계를 이용하여 우리나라의 2차원 토양수분을 산출하였으며, 산출된 장기 토양수분 자료를 이용한 시 공간 변화도 분석을 수행하였다.

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A Study on Sea Water and Ocean Current in the Sea Adjacent to Korea Peninsula -The Vertical Structure of Temperatures in the East Sea of Korea- (한반도 근해의 해류 및 해수특성 -한국 동해의 수온의 수직구조-)

  • NA Jung-Yul;LEE Seong-Wook;CHO Kyu-Dae
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.24 no.4
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    • pp.215-228
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    • 1991
  • In the East Sea of Korea the vertical structure functions of the temperature field were evaluated and the characteristic thermal zone was classified by the use of the empirical orthogonal function(EOF) method. The East Sea of Korea within the hydrographic lines of 10-107 of the Fisheries Research and Development Agency of Korea(FRDA) can be divided into three thermal regions by the characteristics of the vertical temperature variability. They are the North Korean Cold Current(NKCC) region near the coast which extends parallel to the north-south direction, the Warm-Core(WC) region which dominates almost all the hydrographic stations of the Line 104 of the FRDA and occupies a few stations of the Line-103 and -105 with its axis at the Line 104, and the East Korea Warm Current(EKWC) region which is bisected into the northern and the southern part by the WC region, respectively. Considering the two most important modes, $85.20-98.20\%$ of the total variance of temperature variation are explained in the NKCC region, $85.20-92.90\%$ in the EKWC region, and$85.50-91.70\%$ in the WC region. The first mode has its peak value at the surface with the annual cycle of variation. The spatial pattern of the first mode portrays a coherent vertical variation in the EKWC region and a clear anti-correlation both in the NKCC region and in the WC region where the zero-crossing depths are loom and 200m, respectively. The second mode of the NKCC region is particularly noticeable, haying its peak at loom with coherent vertical variation. To study the time dependency of the vertical structure functions, the extended EOF(EEOF) method was used. The persistence of the first mode is less than 4 months in the study area. The annual variation of the first mode in the NKCC region is different from those in the WC region and in the EKWC region.

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A Study on the Characteristics of Tropical Cyclone Passage Frequency over the Western North Pacific using Empirical Orthogonal Function (경험적 직교함수를 이용한 북서태평양 열대저기압의 이동빈도 특성에 관한 연구)

  • Choi, Ki-Seon;Kang, Ki-Ryong;Kim, Do-Woo;Hwang, Ho-Seong;Lee, Sang-Ryong
    • Journal of the Korean earth science society
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    • v.30 no.6
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    • pp.721-733
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    • 2009
  • A pattern of tropical cyclone (TC) movement in the western North Pacific area was studied using the empirical orthogonal function (EOF) and the best track data from 1951 to 2007. The independent variable used in this study was defined as the frequency of tropical cyclone passage in 5 by 5 degree grid. The $1^{st}$, $2^{nd}$ and $3^{rd}$ modes were the east-west, north-south and diagonal variation patterns. Based on the time series of each component, the signs of first and second mode changed in 1997 and 1991, respectively, which seems to be related to the fact that the passage frequency was higher in the South China Sea for 20 years before 1990s, and recent 20 years in the East Asian area. When the eigen vectors were negative values in the first and second modes and TC moves into the western North Pacific, TC was formed mainly at the east side relatively compared to the case of the positive eigen vectors. The first mode seems to relate to the pressure pattern at the south of Lake Baikal, the second mode the variation pattern around $30^{\circ}N$, and the third mode the pressure pattern around Japan. The first mode was also closely related to the ENSO and negatively related to the $Ni\tilde{n}o$-3.4 index in the correlation analysis with SST anomalies.

Evaluation of characteristics of the domestic drought using EOF analysis and stochastic model (EOF 해석과 추계학적 모형을 이용한 국내 가뭄특성의 평가)

  • Yoo, Chul-Sang;Kim, Dae-Ha;Kim, Sang-Dan;Kim, Kyung-Jun;Kim, Byung-Su;Park, Chang-Yeol
    • Proceedings of the Korea Water Resources Association Conference
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    • 2006.05a
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    • pp.1135-1139
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    • 2006
  • 가뭄은 홍수와 함께 인류역사상 가장 큰 재해로 인식되어 있다. 미해양대기청의 발표에 따르면 20세기 최대 자연재해의 상위 5위 안에 4개의 가뭄이 포함되어 있다. 이러한 기록은 가뭄이 동서고금을 막론하고 국가의 흥망성쇠를 좌우할 만큼 막대한 피해를 입혀왔음을 의미한다. 그러나 가뭄의 해석은 가뭄의 정의 자체가 확실하지 않고 서서히 찾아오는 자연재해이기 때문에 그 시작과 끝을 인식하기 어렵다. 아울러 그 진행속도도 굉장히 느리며 또한 장기간에 걸쳐 지속되는 특성을 가지고 있고 시공간적으로 전파된다. 따라서 가뭄의 해석은 굉장히 까다로운 것이라 할 수 있으며 그 해석방법 또한 다양할 수 밖에 없다. 본 연구에서는 우리나라 전역 59개 지점의 표준강수지수(Standard Precipitation Index) 시계열 자료에 대한 공간적 패턴분석과 시간적인 자료확장을 시도하였다. 경험적 직교함수(Emperical Orthogonal function) 해석을 이용하여 자료의 공간적인 패턴을 확인하였고 EOF 해석에서 나타난 EOF Coefficient Time Series를 추계학적 모형에 적용하여 시간적인 자료 확장을 수행하였다. 이렇게 확장된 긴 기간의 자료를 이용하면 재현기간에 대한 평균적인 가뭄심도를 추출할 수 있으며 실제 나타난 사상의 재현기간이 어느 정도인지 평가할 수 있다. 또한 이렇게 나타난 가뭄심도를 강수부족량으로 환산하여 우리나라 대권역별 물부족량을 평가하였다.

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Spatio-Temporal Drought Quantification using Severity-Area-Frequency Curve (가뭄심도-영향면적-지속기간곡선을 이용한 가뭄의 시공간적 정량화)

  • Kim, Bo-Kyung;Kim, Sang-Dan;Kyoung, Min-Soo;Kim, Hung-Soo
    • Proceedings of the Korea Water Resources Association Conference
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    • 2006.05a
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    • pp.1991-1995
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    • 2006
  • 본 연구에서는 제반 수문학적 문제 해결을 위하여 강우사상에 대해 최대평균우량깊이-유역면적-지속기간 관계곡선의 항목 중 최대평균우량깊이를 가뭄심도의 항으로 대체한 가뭄심도-영향면적-지속기간 관계 곡선의 작성방법을 제시하고자 한다. 제주도를 포함한 우리나라 전역의 기상청 월강수량을 이용하여 SPI 가뭄지수를 산정하고 EOF 기법을 적용하여 공간정보로 축약하였다. 이후 Kriging 기법으로 $6km{\times}6km$의 해상도를 가진 SPI값으로 할당함으로써 격자기반의 가뭄지수 자료의 시간 및 공간특성을 고려할 수 있다. 이에 근거하여 주요 가뭄사상을 식별 및 분석하여 영향면적별 가뭄지수를 산정하고 이에 따라 가뭄심도-가뭄면적-가뭄지속기간 관계곡선을 도시하였다. 관계곡선 작성 결과 각 지속기간에 대하여 특정한 면적 이상에서 가뭄심도가 완만하게 감소하는 형태를 보여 공간적 국지성 및 시간적 단속성이 강한 홍수와는 시 공간적으로 다르게 거동되고 있었으며 가뭄심도의 면적에 따른 감소율은 가뭄분석시의 강우깊이의 면적에 따른 감소율과 비교하였을 때 훨씬 작은 것으로 분석되었다.

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Development of Synthetic Regression Diagram for Analyzing Linear Trend of Sea Surface Height, Temperature, and Salinity around the Korean Marginal Seas (한반도 주변 해역 해수면 및 수온, 염분의 선형 추세 분석을 위한 종합 회귀 도표 개발)

  • LIM, BYEONG-JUN;CHANG, YOU-SOON
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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    • v.21 no.2
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    • pp.67-77
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    • 2016
  • This study developed synthetic regression diagram for analyzing the linear trend of sea surface height, temperature, and salinity around the Korean marginal seas. In situ observed data had been quality controlled and they were verified by EOF comparison with objective analyzed data. From the synthetic regression diagram, we confirmed similar linear regression values with those of previous studies, but additionally provided detailed regression rate of each 5 to 30 year for the total periods of 1983-2013. We expect that quantitative results presented by this study will be useful as standard reference numbers for relevant studies analyzing oceanic long-term trend.

A study on the variations of water temperature and sonar performance using the empirical orthogonal function scheme in the East Sea of Korea (동해에서 경험직교함수 기법을 이용한 수온과 소나성능 변화 연구)

  • Young-Nam Na;Changbong Cho;Su-Uk Son;Jooyoung Hahn
    • The Journal of the Acoustical Society of Korea
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    • v.43 no.1
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    • pp.1-8
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    • 2024
  • For measuring the performance of passive sonars, we usually consider the maximum Detection Range (DR) under the environment and system parameters in operation. In shallow water, where sound waves inevitably interacts with sea surface or bottom, detection generally maintains up to the maximum range. In deep water, however, sound waves may not interact with sea surface or/and bottom, and thus there may exist shadow zones where sound waves can hardly reach. In this situation, DR alone may not completely define the performance of each sonar. For complete description of sonar performance, we employ the concept 'Robustness Of Detection (ROD)'. In the coastal region of the East Sea, the spatial variations of water masses have close relations with DR and ROD, where the two parameters show reverse spatial variations in general. The spatial and temporal analysis of the temperature by employing the Empirical Orthogonal Function (EOF) shows that the 1-st mode represents typical pattern of seasonal variation and the 2-nd mode represents strength variations of mixed layers and currents. The two modes are estimated to explain about 92 % of the variations. Assuming two types of targets located at the depths of 5 m (shallow) and 100 m (deep), the passive sonar performance (DR) gives high negative correlations (about -0.9) with the first two modes. Most of temporal variations of temperature occur from the surface up to 200 m in the water column so that when we assume a target at 100 m, we can expect detection performance of little seasonal variations with passive sonars below 100 m.

Variability and Horizontal Structure of Sea Surface Height Anomaly Estimated from Topex/poseidon Altimeter in the East (Japan) Sea (동해의 Topex/Poseidon 고도계로부터 추정된 해면고도이상치의 수평구조와 변동성)

  • Kim, Eung;Ro, Young-Jae;Kim, Chang-Shik
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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    • v.8 no.2
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    • pp.94-110
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    • 2003
  • This study utilizes the dataset of Topex/Poseidon(T/P) altimeter sea surface height (1992-2000 yr., 286 cycles)to investigate the tempore-spatial variability in the East (Japan) Sea. Optimal interpolation (Ol) technique was applied to the pre-processed T/P dataset (level 2) to produce sea surface height anomaly (SSHA) map on regular grids. Spectral analyses of the timeseries of the SSHA at chosen stations and empirical orthogonal function (EOF) analysis of the SSHA in the entire East Sea were made. Distribution of the SSHA can be divided by the southern and northern regions sharply by the polar front situated in the middle of the East Sea. The southern region under the direct influence of the Tsushima Current exhibits higher amplitude of the SSHA fluctuation, while the northern region does relatively smaller one. The spatio-temporal variability of the SSHA in the East Sea can be characterized by the five modes of the EOFs accounting for more than 85% of the total variance. The first mode dominates the SSHA variation in the entire domain with strong seasonal and inter-annual periods accounting for the 72.3% of the total variance. The other modes (up to 5th account for 14%) are responsible for the SSHA variation associated with the local current system, meandering of the polar frontal axis, and mesoscale eddies. Spectral peaks with significant confluence level show semi-annual, annual and interannual (2, 3-4 years) periods.