• Journal of Environmental Science International
• /
• v.13 no.10
• /
• pp.891-902
• /
• 2004

In order to predict air pollution and Yellow-sand dispersion precisely, it is necessary to clarify the sensitivity of meteorological field input interval. Therefore numerical experiment by atmospheric dynamic model(RAMS) and atmospheric dispersion model(PDAS) was performed for evaluating the effect of temporal and spatial resolution of meteorological data on particle dispersion. The results are as follows: 1) Base on the result of RAMS simulation, surface wind direction and speed can either synchronize upper wind or not. If surface wind and upper wind do not synchronize, precise prediction of Yellow-sand dispersion is strongly associated with upwelling process of sand of particle. 2) There is no significant discrepance in distribution of particle under usage of difference temporal resolution of meteorological information at early time of simulation, but the difference of distribution of particles become large as time goes by. 3) There is little difference between calculated particles distributions in dispersion experiments with high temporal resolution of meteorological data. On the other hand, low resolution of meteorological data occur the quantitative difference of particle density and there is strong tendency to the quantitative difference.

• Journal of Environmental Science International
• /
• v.4 no.4
• /
• pp.345-356
• /
• 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 the Korean earth science society
• /
• v.28 no.5
• /
• pp.613-619
• /
• 2007

Mesoscale low is often observed over the downstream region of the East Sea (or, northwest coast off the Japan Islands) during East-Asia winter monsoon. The low system causes a heavy snowfall at the region. A series of numerical experiments were conducted with the aid of a regional model (MM5 ver. 3.5) to examine the formation mechanism of the mesoscale low. The following results were obtained: 1) A well-developed mesoscale low was simulated by the regional model under real topography, NCEP reanalysis, and OISST; 2) The mesoscale low was simulated under a zonally averaged SST without topography. This implies that the meridional gradient of SST is the main factor in the formation of a mesoscale low; 3) A thermal contrast ($>10^{\circ}C$) of land-sea and topography-induced disturbance served as the second important factor for the formation; 4) Paektu Mountain caused the surface wind to decelerate downstream, which created a more favorable environment for thermodynamic modification than that was found in a flat topography; and 5) The types of cumulus parameterizations did not affect the development of the mesoscale low.

• Korean Journal of Remote Sensing
• /
• v.25 no.6
• /
• pp.465-474
• /
• 2009

Convective/stratiform radar echo classification schemes by Steiner et al. (1995) and Biggerstaff and Listemaa (2000) are examined on a monsoonal front during the summer monsoon-Changma period, which is organized as a cloud cluster with mesoscale convective complex. Target radar is S-band with wavelength of 10cm, spatial resolution of 1km, elevation angle interval of 0.5-1.0 degree, and minimum elevation angle of 0.19 degree at Jindo over the Korean Peninsula. For verification of rainfall amount retrieved from the echo classification, ground-based rain gauge observations (Automatic Weather Stations) are examined, converting the radar echo grid data to the station values using the inverse distance weighted method. Improvement from the echo classification is evaluated based on the correlation coefficient and the scattered diagram. Additionally, an optimal use method was designed to produce combined rainfalls from the radar echo and Tropical Rainfall Measuring Mission Precipitation Radar (TRMM/PR) data. Optimal values for the radar rain and TRMM/PR rain are inversely weighted according to the error variance statistics for each single station. It is noted how the rainfall distribution during the summer monsoon frontal system is improved from the classification of convective/stratiform echo and the use of the optimal use technique.

• Journal of the Korean earth science society
• /
• v.40 no.1
• /
• pp.1-8
• /
• 2019

Although recent reports suggest that the negative correlation between the Arctic Oscillation (AO) and the East Asian winter monsoon (EAWM) has been strengthened, it is not clear whether this intermittent relationship is an intrinsic oscillation in the climate system. We investigate the oscillating behavior of the AO-EAWM relationship at decadal time scales using the long-term (500-yr) climate model simulation. The results show that ice cover over the East Siberian Seas is responsible for the change in the coupling strength between AO and EAWM. We found that increased ice cover over these seas strengthens the AO-EAWM linkage, subsequently enhancing cold advection over the East Asia due to anomalous northerly flow via a weakened jet stream. Thus, this strengthened relationship favors more frequent occurrences of cold surges in the EAWM region. Results also indicate that the oscillating relationship between AO and EAWM is a natural variability without anthropogenic drivers, which may help us understand the AO-EAWM linkage under climate change.

• Ocean and Polar Research
• /
• v.40 no.4
• /
• pp.289-297
• /
• 2018

This study reconstructs past vegetation changes in southeastern Korea over the last 30 thousand years using plant waxes (i.e. long chain n-alkanes) and their carbon isotopic compositions (${\delta}^{13}C_{alk}$) preserved in marine sediment core (KIODP 12-1) retrieved from the East Sea. Here we show changes in vegetation composition in the Korean peninsula in relation to the strength of the East Asian Summer Monsoon. During the Last Glacial Maximum (LGM), when the summer monsoon weakened, precipitation decreased and $C_3$ grassland expanded. After the LGM, the summer monsoon gradually intensified, increasing rainfall, and thus expanding the forestland coverage. Precipitation climaxed from 10 to 6 kyr BP, which includes the Holocene Climate Optimum. The grassland began to expand since 5 kyr BP due to climate warming and drying towards the present. The ${\delta}^{13}C_{alk}$ values may also have been influenced by agricultural activities, which is known to have begun since the late Neolithic (ca. 7.0~3.0 kyr BP). Our results demonstrate how changes in the global climate state influence regional atmospheric circulation and precipitation distribution, and consequently terrestrial plant composition in southeastern Korea.

• Ocean Systems Engineering
• /
• v.12 no.4
• /
• pp.403-411
• /
• 2022

Annually, about 48-60% of sediment discharge of the Mekong River is delivered near the mouths of the Mekong River branches which is mostly coinciding with the southwest (SW) monsoon. This sediment budget in turn will be southwestwardly transported along the coast of the Mekong Delta (MD) during the northeast (NE) monsoon. Analysis of monsoonal changes in grain-size distribution (GSD) of surface sediment contributes to a better understanding of erosion and deposition processes along the MD. This study aims to figure out changes in GSD and sediment textures along the MD between SW and NE monsoons based on 183 surficial sediment samples collected along the MD during two field surveys carried-out in October 2016 and February-March 2017. Compared to the GSD during the SW and NE monsoon, the GSD along the MD changed significantly, especially in the estuary areas and along the coast of Bac Lieu and Ganh Hao. Whereas, in the west coast of the MD, GSD seem no changes between the two seasons. These changes in seabed sediment suggest that sediment with grain-sizes ranging from silt to fine sand can be transported during only a NE season.

• Atmosphere
• /
• v.34 no.3
• /
• pp.257-271
• /
• 2024

In 2023, the World Meteorological Organization released a report on climate conditions in Asia, highlighting the region's high vulnerability to floods and the increasing severity and frequency of extreme precipitation events. While previous studies have largely concentrated on broader-scale phenomena such as the Asian monsoon, it is crucial to investigate the substantial characteristics of extreme precipitation for a better understanding. In this study, we analyze the spatiotemporal characteristics of extreme precipitation during summer and their affecting factors by decomposing the moisture budgets within specific Asian regions over 44 years (1979~2022). Our findings indicate that dynamic convergence terms (DY CON), which reflect changes in wind patterns, primarily drive extreme rainfall across much of Asia. In southern Asian sub-regions, particularly coastal areas, extreme precipitation is primarily driven by low-pressure systems, with DY CON accounting for 70% of the variance. However, in eastern Asia, both thermodynamic advection and nonlinear convergence terms significantly contribute to extreme precipitation. Notably, on the Korean Peninsula, thermodynamic advection plays an important role, driven by substantial moisture carried by strong southerly mean flow. Understanding these distinct characteristics of extreme rainfall across sub-regions is expected to enhance both predictability and resilience.

• Korean Journal of Ecology and Environment
• /
• v.40 no.2
• /
• pp.223-233
• /
• 2007

For this study, we analyzed spatial and temporal patterns of trophic state and water quality over the period of $2002{\sim}2005$, using the water chemistry dataset obtained from the Korea Rural community & Agriculture corporation. Most reservoirs, based on TN, showed eutrophic (about 88% of the total). About 20% of agricultural reservoirs, based on TP, showed eutrophic after the criteria of OECD (1982), while 71% and 3% were Hesotrophic and oligotrophic, respectively. Seasonal variations were evident due to the intense monsoon rain during July${\sim}$August; conductivity, COD, SS, nutrients, and chlorophyll-${\alpha}$ (CBL) increased in the postmonsoon compared to the premonsoon. TP values had positive functional relations with conductivity, COD, and CHL values. COD and SS peaked during the intense monsoon. Mean values of TP and CHL values were two times greater in the intense monsoon than the weak monsoon. The increased TP was probably due to inorganic suspended solids from point and non-point sources during the monsoon. Ratios of TN : TP had strong in- verse relations ($R^2$=0.843, p<0.001, n=34) with TP, but not with TN (p>0.05, n=34). Log10-transformed CHL increased with TP in most P-limited reservoirs $(Log_{10}TP=0.5{\times}Log_{10}CHL+0.086)$. Similarity analysis, based TN, TP, and CHL showed that three groups were separated at 90% similarity level; One group was reservoirs with high salinity nearby the seawater, and the other two groups were reservoirs with a low salinity of the inland, and intermediate salinity, respectively.

• Korean Journal of Environmental Biology
• /
• v.18 no.2
• /
• pp.215-226
• /
• 2000

We evaluated the aquatic ecosystem of Keum-Ho River through applications of the Index of Biological Integrity (IBI) using fish assemblages and Qualitative Habitat Evaluation Index (QHEI) during June-November 1999. Overall IBI values ranged from 13 to 37 with mean of 23 (n=25, Std. error= 1.16), indicating a "Poor" or "Very Poor" condition according to the criteria of Karr (1981) and U.S. EPA (1993). The values of mean IBI declined at the rate of $0.22km^{-1}$(($r^2$=0.91, p< 0.05) along the longitudinal distance from the headwaters to the down-river. Reduced IBI values at down-river (St. 4 and 5) were attributed to the decreases in riffle benthic species and the relative abundance of insectivore and increases in tolerant species, anormalies and exotic species. Spatial pattern in IBI agreed with QHEI values, which showed a linear relation ($r^2$=0.998, p< 0.001) with mean number of species. Field measurements of conductivity and pH, indicators for variation of conservative ions, showed that the river water was diluted up to 30% by summer precipitation and surface run-off from the watershed, resulting in physical and chemical instability during the monsoon. For these reasons, average IBI values during monsoon and postmonsoon decreased more than 20% compared to pre -monsoon. Before the perturbation of the system (i.e., pre-monsoon), values of QHEI were inversely correlated (r=-0.99, p< 0.0001) with realtive abundance of native omnivore and were positively correlated (r=0.87, p=0.05) with relative abundance of native carnivore. These results indicate that spatial degradation of habitat quality modified the species richness and trophic structure, producing decreased IBI values. (Biological integrity, IBI, Monsoon, Habitat, River, Korea)bitat, River, Korea)