• Journal of the Korean earth science society
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• v.29 no.3
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• pp.263-279
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• 2008

This study is concerned with the optimization of models using MM5 and WRF mesoscale numerical models to simulate strong sea surface winds, such as that of typhoon Shanshan on 17 September 2006, and the Siberian high event on 16 December 2006, which were selected for displaying the two highest mean wind speeds. The model optimizations for the lowest level altitude, physical parameters and horizontal resolution were all examined. The sea surface wind values obtained using a logarithmic function which takes into account low-level stability and surface roughness were more accurate than those obtained by adjusting the lowest-level of the model to 10 m linearly. To find the optimal parameters for simulating strong sea surface winds various physical parameters were combined and applied to the model. Model grid resolutions of 3-km produced better results than those of 9-km in terms of displaying accurately regions of strong wind, low pressure intensities and low pressure mesoscale structures.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.3
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• pp.57-64
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• 2010

The impacts of climate change on yield and evapotranspiration of rice have been modeled using AquaCrop model developed by Food and Agriculture Organization (FAO). Climate change scenario downscaled by Mesoscale Model 5 (MM5) regional model from ECHO-G General Circulation Model (GCM) outputs by Korea Meteorological Research Institute (METRI) was used in this study. Monthly average climate data for baseline (1971-2000) and three time periods (2020s, 2050s and 2080s) were used as inputs to the AquaCrop model. The results showed that the evapotranspiration after transplanting was projected to increase by 4 % (2020s), 8 % (2050s) and 14 % (2080s), respectively, from the baseline value of 464 mm. The potential rice yield was 6.4 t/ha and water productivity was 1.4 kg/$m^3$ for the baseline. The potential rice yield was projected to increase by 23 % (2020s), 55 % (2050s), and 98 % (2080s), respectively, by the increased photosynthesis along with the $CO_2$ concentration increases. The water productivity was projected to increase by 19 % (2020s), 44 % (2050s), and 75 % (2080s), respectively.

• Interaction and multiscale mechanics
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• v.5 no.2
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• pp.91-104
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• 2012

There is relatively little numerical study on the behavior of eccentrically loaded high strength rectangular concrete-filled steel tubular (CFST) slender beam-columns with large depth-to-thickness ratios, which may undergo local and global buckling. This paper presents a multiscale numerical model for simulating the interaction local and global buckling behavior of high strength thin-walled rectangular CFST slender beam-columns under eccentric loading. The effects of progressive local buckling are taken into account in the mesoscale model based on fiber element formulations. Computational algorithms based on the M$\ddot{u}$ller's method are developed to obtain complete load-deflection responses of CFST slender beam-columns at the macroscale level. Performance indices are proposed to quantify the performance of CFST slender beam-columns. The accuracy of the multiscale numerical model is examined by comparisons of computer solutions with existing experimental results. The numerical model is utilized to investigate the effects of concrete compressive strength, depth-to-thickness ratio, loading eccentricity ratio and column slenderness ratio on the performance indices. The multiscale numerical model is shown to be accurate and efficient for predicting the interaction buckling behavior of high strength thin-walled CFST slender beam-columns.

• Computers and Concrete
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• v.33 no.6
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• pp.671-688
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• 2024

The modeling efficiency of concrete meso-models close to real concrete is one of the important issues that limit the accuracy of mechanical simulation. In order to improve the modeling efficiency and the closeness of the numerical aggregate shape to the real aggregate, this paper proposes a method for generating a two-dimensional concrete meso-model based on pixel matrix and skeleton theory. First, initial concrete model (a container for placing aggregate) is generated using pixel matrix. Then, the skeleton curve of the residual space that is the model after excluding the existing aggregate is obtained using a thinning algorithm. Finally, the final model is obtained by placing the aggregate according to the curve branching points. Compared with the traditional Monte Carlo placement method, the proposed method greatly reduces the number of overlaps between aggregates by up to 95%, and the placement efficiency does not significantly decrease with increasing aggregate content. The model developed is close to the actual concrete experiments in terms of aggregate gradation, aspect ratio, asymmetry, concavity and convexity, and old-new mortar ratio, cracking form, and stress-strain curve. In addition, the cracking loss process of concrete under uniaxial compression was explained at the mesoscale.

• Journal of the Korean earth science society
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• v.25 no.2
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• pp.94-108
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• 2004

In order to clarify the efficiency of ground level change in Ice-valley on atmospheric circulation, numerical experiment was carried out. The circulations over the slope in North and South are different due to the topography and short wave radiation in Ice-valley. Therefore the circulations in both side are asymmetric and the asymmetric circulations are kept on at 1800 LST. A small difference of the atmospheric circulations formation is made due to the road construction at night. The reason may be the weakness of sensible heat flux from the road and other factors except that the sensible heat is not a principal factor in road construction. The construction of road is associated with growing of sensible heat from the road surface. For this reason, in case of daytime, ascending wind in north slope is more stronger with the road than that without road. The maximum wind speed becomes 4.67 m/s after road construction. And the position of the road is also an important factor in estimation of mesoscale circulation in mountainous area.

• Journal of Environmental Science International
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• v.14 no.11
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• pp.1015-1026
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• 2005

The southeastern coastal area of the Korean peninsula has a complex terrain including an irregular coastline and moderately high mountains. This implies that mesoscale circulations such as mountain-valley breeze and land-sea breeze can play an important role in wind field and ocean forcing. In this study, to improve the accuracy of complex coastal rind field(surface wind and sea surface wind), we carried out the sensitivity experiments based on PBL schemes in PSU/NCAR Mesoscale Model (MM5), which is being used in the operational system at Korea Meteorological Administration. Four widely used PBL parameterization schemes in sensitivity experiments were chosen: Medium-Range Forecast (MRF), High-resolution Blackadar, Eta, and Gayno-Seaman scheme. Thereafter, case(2004. 8. 26 - 8. 27) of weak-gradient flows was simulated, and the time series and the vertical profiles of the simulated wind speed and wind direction were compared with those of hourly surface observations (AWS, BUOY) and QuikSCAT data. In the simulated results, the strength of rind speed of all schemes was overestimated in complex coastal regions, while that of about four different schemes was underestimated in islands and over the sea. Sea surface wind using the Eta scheme showed the highest wind speed over the sea and its distribution was similar to the observational data. Horizontal distribution of the simulated wind direction was very similar to that of real observational data in case of all schemes. Simulated and observed vertical distribution of wind field was also similar under boundary layer(about 1 km), however the simulated wind speed was underestimated in upper layer.

• Atmosphere
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• v.24 no.3
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• pp.343-364
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• 2014

This study presents local and synoptic conditions associated with extreme heavy snowfall events in the Yeongdong region, as well as the temporal and spatial variability of these conditions. During the last 12 years (2001~2012), 3 extreme snowfall events occurred in the Yeongdong region, which recorded daily snowfall greater than 50 cm, respectively. In these events, one of the noticeable features is the occurrence of heavy hourly snowfall greater than 10 cm. It was reported from satellite analysis that these heavy snowfall may be closely related to mesoscale convective clouds. In this paper the 3 extreme events are examined on their synoptic environments associated with the developments of mesoscale convective system using numerical model output. These 3 events all occurred in strongly forced synoptic environments where 500 and 300 hPa troughs and 500 hPa thermal troughs were evident. From the analysis of diagnostic variables, it was found in all 3 events that absolute vorticity and cold air advection were dominant in the Yeongdong region and its surrounding sea at upper levels, especially at around 500 hPa (absolute vorticity: $20{\sim}60{\times}10^{-5}s^{-1}$, cold air advection: $-10{\sim}-20^{\circ}C$ $12hr^{-1}$). Moreover, the spatial distributions of cold advection showed mostly the shape of a narrow band along the eastern coast of Korea. These features of absolute vorticity and cold advection at 500 hPa were sustained for about 10 hours before the occurrence of maximum hourly snowfall.

• Atmosphere
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• v.27 no.4
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• pp.455-466
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• 2017

In Korea, property and human damages occur annually due to heavy precipitation during the summer. On August 8, 2015, heavy rainfall occurred in the Seoul metropolitan area due to an outflow boundary, and $77mmhr^{-1}$ rainfall was recorded in Gwangju, Gyeonggi Province. In this study, the simulation of the WRF numerical model is performed to understand the cause and characteristics of heavy rainfall using the Conditional Instability of the Second Kind (CISK), potential vorticity (PV), frontogenesis function, and convective available potential energy (CAPE) analyses, etc. Convective cells initiated over the Shandong Peninsula and located on the downwind side of an upper level trough. Large amounts of water vapor were supplied to the Shandong Peninsula along the southwestern edge of a high pressure system, and from the remnants of typhoon Soudelor. The mesoscale convective system (MCS) developed through CISK process and moved over to the Yellow Sea. The outflow boundary from the MCS progressed east and pushed cold pool eastward. The warm and humid air over the Korean Peninsula further enhanced convective development. As a result, a new MCS developed rapidly over land. Because of the latent heat release due to convection and precipitation, strong potential vorticity was generated in the lower atmosphere. The rapid development of MCS and the heavy rainfall occurred in an area where the CAPE value was greater than $1300Jkg^{-1}$ and the fronto-genesis function value of 1.5 or greater coincided. The analysis result shows that the MCS driven by an outflow boundary can be identified using CISK process.

• Journal of Environmental Science International
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• v.18 no.11
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• pp.1271-1281
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• 2009

The heavy snowfall event over the eastern part of Seoul, Korea on Mar. 04, 2008 has been abruptly occurred after the frontal system with the heavy snowfall event had been past over the Korean peninsula on Mar. 03, 2008. Therefore, this heavy snowfall event couldn't be predicted well by any means of theoretical knowledges and models. After the cold front passed by, the cold air mass was flown over the peninsula immediately and became clear expectedly except the eastern part and southwestern part of peninsula with some large amount of snowfall. Even though the wide and intense massive cold anticyclone was expanded and enhanced by the lowest tropospheric baroclinicity over the Yellow Sea, but the intrusion and eastward movement of cold air to Seoul was too slow than normally predicted. Using the data of numerical model, satellite and radar images, three dimensional analysis Products(KLAPS : Korea Local Analysis and Prediction System) of the environmental conditions of this event such as temperature, equivalent potential temperature, wind, vertical circulation, divergence, moisture flux divergence and relative vorticity could be analyzed precisely. Through the analysis of this event, the formation and westward advection of lower cyclonic circulation with continuously horizontal movement of air into the eastern part of Seoul by the analyses of KLAPS fields have been affected by occurring the heavy snowfall event. As the predictability of abrupt snowfall event was very hard and dependent on not only the synoptic atmospheric circulation but also for mesoscale atmospheric circulation, the forecaster can be predicted well this event which may be occurred and developed within the very short time period using sequential satellite images and KLAPS products.

• Journal of Ecology and Environment
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• v.40 no.2
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• pp.107-119
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• 2016

Background: Previous studies on the biological integrity on habitat and landuse patterns demonstrated ecological stream health in the view of regional or macrohabitat scale, thus ignored the mesoscale habitat patterns of pool, riffle, and runs in the stream health analysis. The objective of this study was to analyze influences on the mesohabitat structures of pool, riffle, and run reaches on the fish guilds and biological integrity in Geum-River Watershed. Results: The mesohabitat structures of pool, riffle, and run reaches influenced the ecological stream health along with some close relations on the fish trophic and tolerance guilds. The mesoscale components altered chemical water quality such as nutrients (TN, TP) and BOD and these, then, determined the primary productions, based on the sestonic chlorophyll-a. The riffle-reach had good chemical conditions, but the pool-reach had nutrient enrichments. The riffle-reach had a predominance of insectivores, while the pool-reach has a predominance of omnivores. Also, the riffle-reach had high proportions of sensitive fish and insectivore fish, and the pool-reach had high proportions of tolerant species in the community composition. The intermediate fish species in tolerance and omnivorous fish species in the food linkage dominated the community in the watershed, and the sensitive and insectivorous fishes decreased rapidly with a degradation of the water quality. All the habitat patterns were largely determined by the land-use patterns in the watershed. Conclusions: Trophic guilds and tolerance guilds of fish were determined by land-use pattern and these determined the stream health, based on the Index of Biological Integrity. This study remarks the necessity to include additional variables to consider information provided by mesohabitats and land-use distributions within the selected stream stretch. Overall, our data suggest that land-use pattern and mesohabitat distribution are important factors to be considered for the trophic and tolerance fish compositions and chemical gradients as well as ecological stream health in the watershed.