• 한국해양학회지
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• v.18 no.1
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• pp.64-72
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• 1983

A series of sheps-of-opportunity sea sryface temperature (SST) measurement beween Jeju and Wando during a period from December 1979 through June 1981 produced following results. 1. A sihnificantly warm water appeared south of Chuja Island and Cheongsan Island during Island. It is suggested that this water represents a current entering the Jeju Strait from the west. Direction of this currint in other seasons is not certain. 2. Coastal waters were found north of the Cheongsan Island and Bogil Islhnd throughout the measurement period. In February these waters sometimes reached as far as Chuja Island to south. 3. Frequently thermal fronts were observed near the Chuja Island and the Cheongsan Island. 4. In summer cold waters appeared north of the Chuja Island and Changsu Island. Intrusion of cold bottom water from offshore and its subsequent vertical mixing due to strong tidal current are probably reponsible for this appearance. 5. Cold waters also appeared locally around islands and in ghe Jeju Harbor in spring and summer. 6. North-south SST difference reached 8-9$^{\circ}C$ in winter which is the annual maximum. 7. Annual range of SST varies from 12-14$^{\circ}C$ in the central part of the Jeju Strait to 16-20$^{\circ}C$ in coastal waters to north. The highest SST appeared everywhere in September but the lowest one did not appesr in the same month of year.

• Journal of Korea Water Resources Association
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• v.45 no.3
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• pp.275-290
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• 2012

In this study, we have developed an optimal time distribution model through extraction of peaks over threshold (POT) series. The median values for annual maximum rainfall dataset, which are obtained from the magnetic recording (MMR) and the automatic weather system(AWS) data at Seoul meteorological observatory, were used as the POT criteria. We also suggested the improved methodology for the time distribution of extreme rainfall compared to Huff method, which is widely used for time distributions of design rainfall. The Huff method did not consider changing in the shape of time distribution for each rainfall durations and rainfall criteria as total amount of rainfall for each rainfall events. This study have suggested an extracting methodology for rainfall events in each quartile based on interquartile range (IQR) matrix and selection for the mode quartile storm to determine the ranking cosidering weighting factors on minutely observation data. Finally, the optimal time distribution model in each rainfall duration was derived considering both data size and characteristics of distribution using kernel density function in extracted dimensionless unit rainfall hyetograph.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.6
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• pp.413-427
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• 1991

Variability of sea levels at Mukho and Ullungdo and sea level difference(SLD) associated with current is investigated. Time series of adjusted sea levels at both places have very similar pattern of change. Two components appear to contribute to the correlation between sea level and SLD. Low frequency thermosteric effect causes the sea level to rise and fall at the same time. Geostrophic effect of major currents is responsible for the sea level change in opposite ways at both sides. Two contributions have a cancelling effect for sea level change at Mukho while they are additive at Ullungdo. Characteristics of time series in frequency domain are divided into two parts with respect to 0.01 cycles per day(cpd). At Mukho, the cancelling effect yields small values of coherence for low-frequency bands whereas the dominant geostrophic influence may be responsible for the phase relations of about $\pm 180^{\circ}$ between sea level and SLD at higher frequency. Bimonthly dynamic height difference(DHD) between Mukho and Ullungdo is very significantly correlated with SLD. This result suggests that DHD thus the average velocity of current through the Mukho-Ullungdo section can successfully be diagnosed by the sea level records at both locations. For the annual variations, maximum SLD occurs at Mukho-Ullungdo section about 40 days later than the Korea Strait.

• Journal of Korea Water Resources Association
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• v.46 no.1
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• pp.47-58
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• 2013

Recently, an increase in the occurrence of sudden local flooding of great volume and short duration due to global climate changes has occasioned the significant danger and loss of life and property in Korea as well as most parts of the world. Such a local flood that usually occurs as the result of intense rainfall over small regions rises quite quickly with little or no advance warning time to prevent flood damage. To prevent the local flood damage, it is important to quickly predict the flood severity for flood events exceeding a threshold discharge that may cause the flood damage for inland areas. The aim of this study is to develop the NFI (New Flood Index) measuring the severity of floods in small ungauged catchments for use in local flood predictions by the regression analysis between the NFI and rainfall patterns. Flood runoff hydrographs are generated from a rainfall-runoff model using the annual maximum rainfall series of long-term observations for the two study catchments. The flood events above a threshold assumed as the 2-year return period discharge are targeted to estimate the NFI obtained by the geometric mean of the three relative severity factors, such as the flood magnitude ratio, the rising curve gradient, and the flooding duration time. The regression results show that the 3-hour maximum rainfall depths have the highest relationships with the NFI. It is expected that the best-fit regression equation between the NFI and rainfall characteristics can provide the basic database of the preliminary information for predicting the local flood severity in small ungauged catchments.

• Journal of the Korean earth science society
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• v.42 no.6
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• pp.632-645
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• 2021

Satellite sea surface temperature (SST) composites provide important data for numerical forecasting models and for research on global warming and climate change. In this study, six types of representative SST composite database were collected from 2007 to 2018 and the characteristics of spatial structures of SSTs were analyzed in seas around the Korean Peninsula. The SST composite data were compared with time series of in-situ measurements from ocean meteorological buoys of the Korea Meteorological Administration by analyzing the maximum value of the errors and its occurrence time at each buoy station. High differences between the SST data and in-situ measurements were detected in the western coastal stations, in particular Deokjeokdo and Chilbaldo, with a dominant annual or semi-annual cycle. In Pohang buoy, a high SST difference was observed in the summer of 2013, when cold water appeared in the surface layer due to strong upwelling. As a result of spectrum analysis of the time series SST data, daily satellite SSTs showed similar spectral energy from in-situ measurements at periods longer than one month approximately. On the other hand, the difference of spectral energy between the satellite SSTs and in-situ temperature tended to magnify as the temporal frequency increased. This suggests a possibility that satellite SST composite data may not adequately express the temporal variability of SST in the near-coastal area. The fronts from satellite SST images revealed the differences among the SST databases in terms of spatial structure and magnitude of the oceanic fronts. The spatial scale expressed by the SST composite field was investigated through spatial spectral analysis. As a result, the high-resolution SST composite images expressed the spatial structures of mesoscale ocean phenomena better than other low-resolution SST images. Therefore, in order to express the actual mesoscale ocean phenomenon in more detail, it is necessary to develop more advanced techniques for producing the SST composites.

• Journal of Korea Water Resources Association
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• v.37 no.12
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• pp.1019-1032
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• 2004

Flood frequency estimate is an essential index for determining the scale of small and middle hydraulic structure. However, this flood quantity could not be estimated directly for practical design purpose due to the lack of available flood data, and indirect method like design rainfall-runoff method have been used for the estimation of design flood. To give the good explain for design flood estimates, regional flood frequency analysis was performed by flood index method in this study. First, annual maximum series were constructed by using the collected data which covers from Japanese imperialism period to 1999. Wakeby distribution recommended by WMO(1989) was used for regional flood frequency analysis and L-moment method by Hosking (1990) was used for parameter estimation. For the homogeneity of region, the discordance and heterogeneity test by Hosking and Wallis(1993) was carried for 4 major watersheds in Korea. Physical independent variable correlated with index flood was watershed area. The relationship between specific discharge and watershed area showed a type of power function, i.e. the specific discharge decreases as watershed area increases. So flood quantity according to watershed area and return period was presented for each watershed(Han rivet, Nakdong river, Geum river and Youngsan/Seomjin river) by using this relation type. This result was also compared with the result of point frequency analysis and its regionalization. It was shown that the dam construction couldn't largely affect the variation of peak flood. The property of this study was also examined by comparison with previous studies.

• Journal of Korea Water Resources Association
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• v.45 no.8
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• pp.815-826
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• 2012

The underestimating trend using existing ordinary regression (OR) based trend analysis has been a well-known problem. The existing OR method based on least squares approximate the conditional mean of the response variable given certain values of the time t, and the usual assumption of the OR method is normality, that is the distribution of data are not dissimilar form a normal distribution. In this regard, this study proposed a quantile regression that aims at estimating either the conditional median or other quantiles of the response variable. This study assess trend in annual daily maximum rainfall series over 64 weather stations through both in OR and QR approach. The QR method indicates that 47 stations out of 67 weather stations are a strong upward trend at 5% significance level while OR method identifies a significant trend only at 13 stations. This is mainly because the OR method is estimating the condition mean of the response variable. Unlike the OR method, the QR method allows us flexibly to detect the trends since the OR is designed to estimate conditional quantiles of the response variable. The proposed QR method can be effectively applied to estimate hydrologic trend for either non-normal data or skewed data.

• The Korean Journal of Pesticide Science
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• v.18 no.4
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• pp.236-246
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• 2014

Pesticide is used to protect the crops, but also become a cause of polluting the environment. Perform a risk assessment using physical and chemical properties, environmental fate and toxicity data in order to determine the pesticide registration. The aquatic model estimates pesticide concentrations in water bodies that result from pesticide applications to rice paddies and apple orchard. The used models are the PRZM, EXAMS and AGRO shell (PA5), Rice Water Quality Model (RICEWQ) and Screening Concentration In GROund Water (SCI-GROW). The residual concentration of water body was estimated using meteorological data, crop calendar and soil series of Korea. The chosen pesticides were butachlor, carbofuran, iprobenfos and tebuconazole. It has shown the potential that the RICEWQ is possible to predict residue level in water of butachlor and iprobenfos, because the maximum value in water monitoring data is lower than the peak concentration of the model, and the minimum value is lower than the average annual concentration of the model. But RICEWQ was insufficient to predict exposure concentrations in ground water. The estimated exposure concentrations of carbofuran in ground water is very higher than in surface water because of its low soil adsorption coefficient. Although tebuconazole were not detected in the water monitoring that means very low concentration, it is possible that the PA5 can be used to predict residue level in water.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.497-512
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• 2017

Temporal and spatial variations in surface water temperature were studied using data from temperature monitoring buoys deployed at 47 stations around Boryeong from 2011-2012 off the west coast of Korea. Temperature fluctuations are predominant at diurnal and semidiurnal periods for all seasons, and their amplitudes are large in spring and summer but small in autumn. The maximum annual change in air temperature takes place on August 2nd and August 22th for water temperature, which means the phase for air temperature precedes water temperature by 20 days. The diurnal period of water temperature fluctuation is predominant around Daecheon and Muchangpo Harbors, with the semidiurnal period around Wonsan Island, and the shallow water constituent period on the estuary around Daecheon River. On the whole, air and water temperatures fluctuate with wind. Spectral analyses of temperature records show significant peaks at the 0.5, 1 and 15 day marks with 7-10 day periods of predominant fluctuations. Cross-correlation analyses for the temperature fluctuation show that the waters around Boryeong can be classified into four areas: a mixed water zone around the southeast side of Wonsan Island, an off-shore area to the west, an off-shore area to the south and a coastal area along the shore from Song Island to Muchangpo Harbor.

• Atmosphere
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• v.24 no.4
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• pp.481-489
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• 2014

The Chugugi and Wootaek data of Gyeongsang-do (Dagu, Jinju, Goseong) were restored from "Gaksadeungnok", the governmental documents reported by the local government to the central during the Joseon Dynasty, and analyzed. The duration of the restored data represents 6 years for Daegu (1863, 1872, 1890, 1897, 1898, and 1902), 3 years for Jinju (1897, 1898, and 1900), and 2 years for Goseong (1871 and 1873). Total number of the restored data was 134, including 83 in Daegu, 25 in Jinju, and 26 in Goseong with the period ranging from March to September. The summer data from June to August accounts for approximately 50% (73 data), while the April data also shows relatively high number of 22, followed by September and March. Most data was collected from March to October, while this time winter data was not found even in October. The rainfall patterns using Chugugi data were investigated. First, the number of days with rainfall by annual mean showed 41 days in Daegu, 39 in Jinju, 33 in Goseong, respectively. In terms of the time series distribution of daily rainfall, the ratio between the number of occurrences with over 40 mm of heavy rainfall and the number of rainy days showed 14 times (8%) in Daegu, 24 (39%) in Jinju, and 4 (6%) in Goseong, respectively. The maximum daily rainfall during the period was recorded with 80mm in Jinju on August 24, 1900. The result of analyzing monthly amount of rainfall clearly indicated more precipitation in summer (June, July and August) with the relatively high records of 284 mm and 422 mm in April, 1872 and July, 1902, respectively, in Daegu, while Jinju recorded the highest value of 506 mm in June, 1898. When comparing the data with those observed by Chugugi in Seoul during the same period from "Seungjeongwonilgi", the monthly rainfall patterns in Daegu and Seoul were quite similar except for the year of 1890 and 1897 in which many data were missing. In particular, in June 1898 the rainfall amount of Jinju recorded as much as 506 mm, almost 4 times of that of Seoul (134 mm). Based on this, it is possible to presume that there was a large amount of the precipitation in the southern region during 1898. According to the calculated result of Wootaek data based on Chugugi observations, the unit of 1 'Ri' and 1 'Seo' in Daegu can be interpreted into 18.6 mm and 7.8 mm. When taking into consideration with the previous result found in Gyeonggi-do (Cho et al., 2013), 1 'Ri' and 1 'Seo' may be close to 20.5 mm and 8.1 mm, however, more future investigations and studies will be essential to verify the exact values.