• Atmosphere
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• v.21 no.3
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• pp.221-228
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• 2011

The nonlinear characteristics of summer monsoon intraseasonal oscillation (ISO) in precipitation, which is manifested as fluctuations in convection and circulation, is one of the major difficulty on the prediction of East Asian summer monsoon (EASM). The present study aims to identify the spatial distribution and time evolution of nonlinear phases of monsoon ISO. In order to classify the different phases of monsoon ISO, Self-Organizing Map(SOM) known as a nonlinear pattern recognition technique is used. SOM has a great attractiveness detecting self-similarity among data elements by grouping and clustering such self-similar components. The four important patterns are demonstrated as Meiyu-Baiu, Changma, post-Changma, and dry-spell modes. It is found that SOM well captured the formation of East Asian monsoon trough during early summer and its northward migration together with enhanced convection over subtropical western Pacific and regionally intensive precipitation including Meiyu, Changma and Baiu. The classification of fundamental large scale spatial pattern and evolutionary history of nonlinear phases of monsoon ISO provides the source of predictability for extended-range forecast of summer precipitation.

• The Korean Journal of Quaternary Research
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• v.24 no.1
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• pp.1-10
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• 2010

The Indian summer monsoon behaved an abnormal way in 2002 and as a result there was a large deficiency in precipitation (especially in July) over a large part of the Indian subcontinent. For the study of deficient monsoon of 2002, a recent version of the NCAR regional climate model (RegCM3) has been used to examine the important features of summer monsoon circulations and precipitation during 2002. The main characteristics of wind fields at lower level (850 hPa) and upper level (200 hPa) and precipitation simulated with the RegCM3 over the Indian subcontinent are studied using different cumulus parameterization schemes namely, mass flux schemes, a simplified Kuo-type scheme and Emanuel (EMU) scheme. The monsoon circulation features simulated by RegCM3 are compared with the NCEP/NCAR reanalysis and simulated precipitation is validated against observation from the Global Precipitation Climatology Centre (GPCC). Validation of the wind fields at lower and upper levels show that the use of Arakawa and Schubert (AS) closure in Grell convection scheme, a Kuo type and Emanuel schemes produces results close to the NCEP/NCAR reanalysis. Similarly, precipitation simulated with RegCM3 over different homogeneous zones of India with the AS closure in Grell is more close to the corresponding observed monthly and seasonal values. RegcM3 simulation also captured the spatial distribution of deficient rainfall in 2002.

• The Korean Journal of Quaternary Research
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• v.22 no.1
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• pp.13-22
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• 2008

The Indian summer monsoon behaved in an abnormal way in 2002 and as a result there was a large deficiency in precipitation (especially in July) over a large part of the Indian subcontinent. For the study of deficient monsoon of 2002, a recent version of the NCAR regional climate model (RegCM3) has been used to examine the important features of summer monsoon circulations and precipitation during 2002. The main characteristics of wind fields at lower level (850 hPa) and upper level (200 hPa) and precipitation simulated with the RegCM3 over the Indian subcontinent are studied using different cumulus parameterization schemes namely, mass flux schemes, a simplified Kuo-type scheme and Emanuel (EMU) scheme. The monsoon circulation features simulated by RegCM3 are compared with the NCEP/NCAR reanalysis and simulated precipitation is validated against observation from the Global Precipitation Climatology Centre (GPCC). Validation of the wind fields at lower and upper levels shows that the use of Arakawa and Schubert (AS) closure in Grell convection scheme, a Kuo type and Emanuel schemes produces results close to the NCEP/NCAR reanalysis. Similarly, precipitation simulated with RegCM3 over different homogeneous zones of India with the AS closure in Grell is more close to the corresponding observed monthly and seasonal values. RegcM3 simulation also captured the spatial distribution of deficient rainfall in 2002.

• Journal of Environmental Science International
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• v.4 no.4
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• pp.345-356
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• 1995

Examining the precipitation data collected during the period from 1960 to 1993, we found that Taegu Station represents an optimum station for explaining the interannual variations of the precipitation in Korea. Using the variations derived from Taegu, the secular trends of the precipitation in Korea have been studied. It was 삽so found that the interannual variations of summer monsoon precipitation are consistent with those of the annual precipitation. To explore the interannual variations of the summer monsoon precipitation, comparisons of the summer precipitation in Korea with that in China and Japan were made. The results of the empirical orthogonal function analysis showed that Korea, the Yangtze River and Huaihe River valley, and the south Japan are all located in the same climate system during summer. The detailed analysis was carried out on the comparison of the summer precipitation in Korea with that in the eastern part of the the mainland China. We found that the correlation pattern is similar to the East Asia/pacific pattern. The probable effects of the sea surface temperature on the precipitation in Korea were also discussed. Key Words : Precipitation in Korea, rainy seasons in East Asia, monsoon precipitation, interannual variations.

• Journal of Environmental Science International
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• v.23 no.10
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• pp.1719-1729
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• 2014

This study is carried out in order to bridge the gap to understand the relationships between South Asian and East Asian monsoon systems by comparing the summer (June-September) precipitation of Nepal and South Korea. Summer monsoon precipitation data from Nepal and South Korea during 30 years (1981-2010) are used in this research to investigate the association. NCEP/NCAR reanalysis data are also used to see the nature of large scale phenomena. Statistical applications are used to analyze these data. The analyzed results show that summer monsoon precipitation is higher over Nepal ($1513.98{\pm}159.29mm\;y^{-1}$) than that of South Korea ($907.80{\pm}204.71mm\;y^{-1}$) and the wettest period in both the countries is July. However, the coefficient of variation shows that amplitude of interannual variation of summer monsoon over South Korea (22.55%) is larger in comparison to that of Nepal (10.52%). Summer monsoon precipitation of Nepal is found to be significantly correlated to that of South Korea with a correlation coefficient of 0.52 (99% confidence level). Large-scale circulations are studied to further investigate the relationship between the two countries. wind and specific humidity at 850 hPa show a strong westerly from Arabian Sea to BOB and from BOB, wind moves towards Nepal in a northwestward direction during the positive rainfall years. In case of East Asia, strong northward displacement of wind can be observed from Pacific to South Korea and strong anticyclone over the northwestern Pacific Ocean. However, during the negative rainfall years, in the South Asian region we can find weak westerly from the Arabian Sea to BOB, wind is blowing in a southerly direction from Nepal and Bangladesh to BOB.

• Journal of the Korean earth science society
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• v.34 no.1
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• pp.102-106
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• 2013

The intensity of the East Asian summer monsoon has a negative correlation with that of the western North Pacific summer monsoon. Based on the relationship, we suggest the potential predictability of Northeast Asian summer precipitation by using the relationship. The western North Pacific subtropical high (WNPSH) properly represents the intensity of the western North Pacific summer monsoon. It also dominates climate anomalies in the western North Pacific-East Asian region in summertime. The estimates of the Northeast Asian summer rainfall anomalies using WNPSH variability have a greater benefit than those using the western North Pacific monsoon index.

• Atmosphere
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• v.20 no.2
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• pp.111-130
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• 2010

An uncertainty assessment for precipitation datasets simulated by Atmosphere-Ocean Coupled General Circulation Model (AOGCM) is conducted to provide reliable climate scenario over East Asia. Most of results overestimate precipitation compared to the observational data (wet bias) in spring-fall-winter, while they underestimate precipitation (dry bias) in summer in East Asia. Higher spatial resolution model shows better performances in simulation of precipitation. To assess the uncertainty of spatiotemporal precipitation in East Asia, the cyclostationary empirical orthogonal function (CSEOF) analysis is applied. An annual cycle of precipitation obtained from the CSEOF analysis accounts for the biggest variability in its total variability. A comparison between annual cycles of observed and modeled precipitation anomalies shows distinct differences: 1) positive precipitation anomalies of the multi-model ensemble (MME) for 20 models (thereafter MME20) in summer locate toward the north compared to the observational data so that it cannot explain summer monsoon rainfalls across Korea and Japan. 2) The onset of summer monsoon in MME20 in Korean peninsula starts earlier than observed one. These differences show the uncertainty of modeled precipitation. Also the comparison provides the criteria of annual cycle and correlation between modeled and observational data which helps to select best models and generate a new MME, which is better than the MME20. The spatiotemporal deviation of precipitation is significantly associated with lower-level circulations. In particular, lower-level moisture transports from the warm pool of the western Pacific and corresponding moisture convergence significantly are strongly associated with summer rainfalls. These lower-level circulations physically consistent with precipitation give insight into description of the reason in the monsoon of East Asia why behaviors of individually modeled precipitation differ from that of observation.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.174-174
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• 2023

The impact of global warming on the south Asian summer monsoon is of critical importance for the large population of this region. This study aims to investigate the future changes of the precipitation extremes during pre-monsoon and monsoon, across this region in a more organized regional structure. The study area is divided into six major divisions based on the Köppen-Geiger's climate structure and 10 sub-divisions considering the geographical locations. The future changes of extreme precipitation indices are analyzed for each zone separately using five indices from ETCCDI (Expert Team on Climate Change Detection and Indices); R10mm, Rx1day, Rx5day, R95pTOT and PRCPTOT. 10 global climate model (GCM) outputs from the latest CMIP6 under four combinations of SSP-RCP scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) are used. The GCMs are bias corrected using nonparametric quantile transformation based on the smoothing spline method. The future period is divided into near future (2031-2065) and far future (2066-2100) and then the changes are compared based on the historical period (1980-2014). The analysis is carried out separately for pre-monsoon (March, April, May) and monsoon (June, July, August, September). The methodology used to compare the changes is probability distribution functions (PDF). Kernel density estimation is used to plot the PDFs. For this study we did not use a multi-model ensemble output and the changes in each extreme precipitation index are analyzed GCM wise. From the results it can be observed that the performance of the GCMs vary depending on the sub-zone as well as on the precipitation index. Final conclusions are made by removing the poor performing GCMs and by analyzing the overall changes in the PDFs of the remaining GCMs.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.2
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• pp.79-87
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• 1999

$^{239+240}Pu$ concentrations in precipitation were determined for the period of May 1994 to August 1996 in oder to describe current $^{239+240}Pu$ deposition at the mid-western coat of Korea (Ansan, 37$^{\circ}$17'N, $126^{\circ}$50'E). $^{239+240}Pu$ concentration in daily precipitation varied from 0.05 to 131$\mu$Bq $kg^{-1}$ with a geometric mean of $1.26\mu$Bq $kg^{-1}$. The concentration was high in the period of Yellow Sand Storm in spring and low in wet summer monsoon. The specific $^{239+240}Pu$ concentration in daily precipitation appears to be controlled by the $^{239+240}Pu$ input to the atmosphere in spring and washout effects by precipitation in the wet summer monsoon. Wet depositional flux of $^{239+240}Pu$ varied from 4 to 123$\mu$Bq $m^{-2}d^{-1}$ with a geometric mean of $33.8\mu$Bq $m^{-2}d^{-1}$ and with a maximum in the period of Yellow Sand Storm and a minimum in the period of wet summer monsoon. $^{238}Pu$/$^{239+240}Pu$ activity raios(0.04~0.31) in precipitation for March-June period suggested that one of the major sources of Pu isotopes falling in Ansan area is the arid region of the Chinese continent.

• The Korean Journal of Quaternary Research
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• v.17 no.2
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• pp.63-69
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• 2003

Three tree-ring monsoon rainfall reconstructions from China and Korea have been used in this paper to investigate the variation of the East Asian summer monsoon over the past 160 years. Statistically, there is no linear correlation on a year-by-year basis between Chinese and Korean monsoon rainfall, but region-wide synchronous variation on decadal-scale was observed. Strong monsoon intervals (more rainfall) were 1860-1890, 1910-1925,1940-1960, and weak monsoon periods (dry or even drought) were 1890-1910, 1925-1940, 1960- present. Reconstructions also display that the East Asian summer monsoon suddenly changed from strong into weak around mid-1920, and the East Asian summer monsoon keeps going weak after 1960.