• 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.

• Atmosphere
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• v.13 no.2
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• pp.47-68
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• 2003

Recent advances in the studies on the interaction between Asian monsoon and ENSO cycle are reviewed in this paper. Through the recent studies, the East Asian summer monsoon circulation system and the East Asian climate system have proposed. Moreover, different responses of the (winter and summer) monsoon circulation and summer rainfall anomalies in East Asia to ENSO cycle during its different stages have been understood further. Recently, the studies on the dynamical effect of East Asian monsoon on the thermal variability of the tropical western Pacific and ENSO cycle have been greatly advanced. These studies demonstrated further that ENSO cycle originates from the tropical western Pacific, and pointed out that the dynamical effect of East Asian winter and summer monsoons on ENSO cycle may be through the atmospheric circulation and zonal wind anomalies over the tropical western Pacific, which can excite the oceanic Kelvin wave and Rossby waves in the equatorial Pacific. Besides, the scientific problems in the interaction between Asian monsoon and ENSO cycle, which should be studied further in the near future, are also pointed out in this paper.

• Journal of Korean Society on Water Environment
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• v.37 no.6
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• pp.458-468
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• 2021

In this study, we investigated the variations of dissolved organic matter (DOM) in an agricultural reservoir during the monsoon period (June to October, 2020) with respect to the organic carbon concentration (DOC), molecular weight distribution, and optical properties. The monsoon period was divided into three phases - beginning storm (BS), during storm (DS), and after storm (AS). Our results showed significant differences in the concentrations and characteristics of DOM during the summer monsoon. The DOC concentrations were decreased after the monsoon, probably due to a dilution effect. In contrast, increasing trends were observed in the specific UV absorbance (SUVA), and relative abundances of humic-like fluorescence and larger-sized compounds. These observations implied that the large-sized and humic-like organic components with terrestrial origins strongly affected the reservoir DOM after the summer monsoon. Meanwhile, biopolymer size fraction, which is associated with algal activity, became more abundant after the monsoon. These results suggest that DOM with autochthonous sources became dominant as a result of the inflow of nutrients into the reservoir after the storm. Spatial changes in DOM within the reservoir were not pronounced as much as the temporal variations. All taken, it can be concluded that the summer monsoon simply led to the decrease of DOM concentrations while the sources and the quality of DOM underwent substantial changes, which may enrich refractory organic matter in the reservoir. This study reveals the importance of in-depth DOM quality monitoring before and after summer monsoon for effective water quality management in agricultural reservoirs.

• Atmosphere
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• v.22 no.4
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• pp.483-488
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• 2012

The monsoon front lies on East Asian region, but it gradually propagates to the north during the boreal summer. The equivalent potential temperature (EPT) reveals the thermodynamical features of air masses and monsoon front. Therefore, this study considered the thermodynamical EPT and dynamical wind fields to clarify the peculiarity of East Asian summer monsoon (EASM) variations in June and July, respectively. Western North Pacific subtropical high (WNPSH) and Okhotsk sea high (OSH) both play the crucial role to interannual variations of EASM frontal activity and amount of rainfall. The OSH is important in June, but the WNPSH is key factor in July. Furthermore, the OSH (June) is affected by North Atlantic tripolar sea surface temperature (SST) pattern and WNPSH (July) is influenced by North Indian Ocean SST warming.

• 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.

• 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.34 no.3
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• pp.319-323
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• 2024

It has been recognized that interannual relationship between Northeast Asian and western North Pacific (WNP) summer monsoon intensities has a negative correlation with a statistical significance. This teleconnection can be understood by the responses to the stationary Rossby wave, which is forced by variability of the western North Pacific summer monsoon intensity. In addition, the relationship between two monsoon intensities have a large variability on decadal time-scale associated with adjacent climate variability. The study for the recent changes in these long-term relationships has not been reported so far. This study suggests the recent relationship between Northeast Asian and WNP summer monsoons with an extension of the analysis period in the previous studies. Based on the reanalysis datasets, this study also shows atmospheric teleconnection changes associated with El Nino in summertime during the different decadal periods. This study also suggests the possible reasons for the analysis results in terms of teleconnection changes.

• Proceedings of the KSRS Conference
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• 1999.11a
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• pp.325-329
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• 1999

The characteristic of East Asian summer monsoon is investigated using 8-year (March 1987-February 1995) - averaged monthly and 5-day mean 1 degree latitude-longitude gridded GMS high-cloud-amount data (HCA). An analysis of these data shows the convective zone (ITCZ) clouds which defined as the percentage of the total grid area covered by clouds with a cloud-top temperature below the 400 hPa-level climatological temperature. The HCA increased clearly over equatorial zone during December and January and 30-40 $^{\circ}$N during May and June. These HCA patterns are coincided with seasonal cycles of summer monsoon which is introduced in historical references. The relationship with the summer monsoon winds as climatological changing of wind direction is analyzed by ECMWF re-analysis 2.5-degree latitude-longitude grid surface data which is calculated with 8-year averaged from January 1987 to January 1995. In addition, the monsoon winds are showed by separated U, V-wind components far manifestation a tendency of onset and retreat data of seasonal monsoon.

• 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.