• Journal of the Korean association of regional geographers
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• v.11 no.4
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• pp.429-439
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• 2005

The propose of this study is to identify distributional characteristics of winter droughts through occurrence frequencies and to analyze synoptic characteristics on the sea level pressure fields and 500hPa levels in Korea. The regional distributions of winter droughts in occurrence frequency vary according to the monthly regional distributions of the variabilities of precipitation in Korea. In January and December, the eastern parts of Korea where the variabilities of precipitation show high, have high rate of drought frequencies, while the western parts have low rate of it. It means that the regional distribution of the drought frequencies in January and December shows the east-high and west-low pattern, In February the frequencies show the north-high and south-low pattern. In the distributions of the sea-level pressure and 500hPa level height anomalies, the positive anomalies appear around Korean Peninsula and Siberian high area, the negative anomalies on the Aleutian low area and the western parts of North Pacific Ocean during the drought period in January and February. The droughts appear when the inflow of warm and humid air from the south eastern parts blocked by the prevailing pressure patterns of the west-high and east-low. Therefore, the zonal wind of the Korean Peninsula is strong. The droughts of December reflect not only low frequencies of cyclone occurrence, also small inflow of warm and humid air from the southern parts stemming from positive anomalies over whole middle latitude of eastern parts of Asia including Korean Peninsula.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.4
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• pp.242-253
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• 2011

Skin frictional drag reduction efficiency of "stiff" compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.

• Atmosphere
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• v.30 no.2
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• pp.183-193
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• 2020

In this study, Yeongdong cold air damming (YCAD) cases that occur in winters have been selected using automatic weather station data of the Yeongdong region of Korea. The vertical and horizontal scales of YCAD were analyzed using rawinsonde and numerical weather model. YCAD occurred in two typical synoptic patterns such that low pressure and trough systems crossing and passing over Korea (low crossing type: LC and low passing type: LP). When the Siberian high does not expand enough to the Korean peninsula, low pressure and trough systems are likely to move over Korea. Eventually this could lead to surface temperature (3.1℃) higher during YCAD than the average in the winter season (1.6℃). The surface temperature during YCAD, however, was decrease by 1.3℃. The cold air layer was elevated around 120 m~450 m for LP-type. For LC-type, the cold layer were found at less than approximately 400 m and over 1,000 m, which could be thought of combined phenomena with synoptic and local weather forcing. The cross-sectional analysis results indicate the accumulation of cold air on the east mountain slope. Additionally, the north or northeasterly winds turned to the northwesterly wind near the coast in all cases. The horizontal wind turning point of LC-type was farther from the top of the mountain (52.2 km~71.5 km) than that of LP-type (20.0 km~43.0 km).

• Journal of Integrative Natural Science
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• v.17 no.1
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• pp.1-12
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• 2024

Many abnormal climate events are occurring around the world. The cause of abnormal climate is related to temperature. Factors that affect temperature include excessive emissions of carbon and greenhouse gases from a global perspective, and air circulation from a local perspective. Due to the air circulation, many abnormal climate phenomena such as abnormally high temperature and abnormally low temperature are occurring in certain areas, which can cause very serious human damage. Therefore, the problem of abnormal temperature should not be approached only as a case of climate change, but should be studied as a new category of climate crisis. In this study, we proposed a model for the classification of abnormal temperature using random forests based on various meteorological data such as longitudinal observations, yellow dust, ultraviolet radiation from 2018 to 2022 for each region in Korea. Here, the meteorological data had an imbalance problem, so the imbalance problem was solved by oversampling. As a result, we found that the variables affecting abnormal temperature are different in different regions. In particular, the central and southern regions are influenced by high pressure (Mainland China, Siberian high pressure, and North Pacific high pressure) due to their regional characteristics, so pressure-related variables had a significant impact on the classification of abnormal temperature. This suggests that a regional approach can be taken to predict abnormal temperatures from the surrounding meteorological environment. In addition, in the event of an abnormal temperature, it seems that it is possible to take preventive measures in advance according to regional characteristics.

• Journal of the Korean Geographical Society
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• v.45 no.3
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• pp.319-341
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• 2010

The purposes of this study are to classify heavy snowfall types in the Republic of Korea based on fresh snowfall data and atmospheric circulation data during the last 36(1973/74-2008/09) snow seasons and to identify typical surface synoptic climate patterns that characterize each heavy snowfall type. Four synoptic climate categories and seventeen regional heavy snowfall types are classified based on sea level pressure/surface wind vector patterns in East Asia and frequent spatial clustering patterns of heavy snowfall in the Republic of Korea, respectively. Composite analyses of multiple surface synoptic weather charts demonstrate that the locations and intensity of pressure/wind vector mean and anomaly cores in East Asia differentiate each regional heavy snowfall type in Korea. These differences in synoptic climatic fields are primarily associated with the surge of the Siberian high pressure system and the appearance of low pressure systems over the Korean Peninsula. In terms of hemispheric atmospheric circulation, synoptic climatic patterns in the negative mode of winter Arctic Oscillation (AO) are also associated with frequent heavy snowfall in the Republic of Korea at seasonal scales. These results from long-term synoptic climatic data could contribute to improvement of short-range or seasonal prediction of regional heavy snowfall.

• Atmosphere
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• v.23 no.2
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• pp.187-204
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• 2013

This study analyzed the synoptic distribution and vertical structure about four cases of precipitation occurrences using NCEP/NCAR reanalysis data and upper level data of winter intensive observation to be performed by National Institute of Meteorological Research at Bukgangneung, Incheon, Boseong during 63days from 4 JAN to 6 MAR in 2012, and Observing System Experiment (OSE) using 3DVAR-WRF system was conducted to examine the precipitation predictability of upper level data at western and southern coastal regions. The synoptic characteristics of selected precipitation occurrences were investigated as causes for 1) rainfall events with effect of moisture convergence owing to low pressure passing through south sea on 19 JAN, 2) snowfall events due to moisture inflowing from yellow sea with propagation of Siberian high pressure after low pressure passage over middle northern region on 31 JAN, 3) rainfall event with effect of weak pressure trough in west low and east high pressure system on 25 FEB, 4) rainfall event due to moisture inflow according to low pressures over Bohai bay and south eastern sea on 5 MAR. However, it is identified that vertical structure of atmosphere had different characteristics with heavy rainfall system in summer. Firstly, depth of convection was narrow due to absence of moisture convergence and strong ascending air current in middle layer. Secondly, warm air advection by veering wind with height only existed in low layer. Thirdly, unstable layer was limited in the narrow depth due to low surface temperature although it formed, and also values of instability indices were not high. Fourthly, total water vapor amounts containing into atmosphere was small due to low temperature distribution so that precipitable water vapor could be little amounts. As result of OSE conducting with upper level data of Incheon and Boseong station, 12 hours accumulated precipitation distributions of control experiment and experiments with additional upper level data were similar with ones of observation data at 610 stations. Although Equitable Threat Scores (ETS) were different according to cases and thresholds, it was verified positive influence of upper level data for precipitation predictability as resulting with high improvement rates of 33.3% in experiment with upper level data of Incheon (INC_EXP), 85.7% in experiment with upper level data of Boseong (BOS_EXP), and 142.9% in experiment with upper level data of both Incheon and Boseong (INC_BOS_EXP) about accumulated precipitation more than 5 mm / 12 hours on 31 January 2012.

• Journal of the Korean earth science society
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• v.35 no.4
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• pp.237-248
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• 2014

To analyze the characteristics of deposition and dispersion of volcanic ash emitted from Mt. Kirishima on January 26, 2011, several numerical simulations were carried out by using the numerical models including Weather and Research Forecast (WRF) and FLEXPART. The dispersion of ash located under 1 km high tends to be concentrated along the prevailing wind direction on January 26 2011. On the other hand, volcanic ash released on the following day spreads to Kirishima bay due to the intensified high pressure air mass in southern Kyushu. When Siberian air mass was intensified January 26, 2011, the deposition of volcanic ash is concentrated restrictedly in the narrow area along the wind direction of the downwind side of Mt. Kirishima. The development of high pressure air mass over the eruption area tends to induce the intensified horizontal diffusion of volcanic ash. Since the estimated deposition of volcanic ash is agreed well with observed values, the proposed numerical simulation is reasonable to use the assessment on the behavior of volcanic ash.

• Journal of the Semiconductor & Display Technology
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• v.2 no.1
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• pp.1-5
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• 2003

Plasma generator based on non-self-sustained low-pressure arc discharge has been examined as a tool for deposition of highly-adhesive hydrogenated amorphous diamond-like carbon(DLC) films. Since the discharge is stable in wide range of gas pressures and currents, this plasma source makes possible to realize both plasma-immersion ion implantation(PIII) and plasma-immersion ion deposition(PIID) in a unified vacuum cycle. The plasma parameters were measured as functions of discharge current. Discharge and substrate bias voltage parameters have been determined for the PIII and PIID modes. For PIID it has been demonstrated that hard and well-adherent DLC coating are produced at 200-500 eV energies per deposited carbon atom. The growth rates of DLC films in this case are about 200-300 nm/h. It was also shown that short(∼60$\mu\textrm{s}$) high-voltage(> 1kV) substrate bias pulses are the most favorable for achieving high hardness and good adhesion of DLC, as well as for reducing of residual intrinsic stress are.

• Journal of the Korean earth science society
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• v.33 no.4
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• pp.337-349
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• 2012

In this study, we classify the 1000 hPa geopotential height fields around the Korean peninsula through the Kmeans cluster analysis and investigate the occurrence characteristics of each cluster pattern. The 11 clusters are identified as the typical pressure patterns, applying the pattern correlation as a similarity among clusters and the criterion of cluster similarity 0.8, of which three pressure patterns are associated with the extension of Siberia air mass, other three with the latitudes of the longest symmetry axis of North Pacific highs, two with the trough largely under the air mass of Siberia or North Pacific, and the remaining three, the migratory high patterns generally occurring in spring and autumn, are disjointed according to the direction of the longest symmetry axis of highs. The occurrence rate of air masses affecting the Korean peninsula, estimated from the number of occurrence days of 11 pressure patterns, is 55.4% Siberian, 29.3% North Pacific, 12.8% Yangtze-River, 2.5% Okhotsk sea and 68.2% of all these is the continental air masses. The wintertime pressure patterns around the Korean peninsula are nearly contrary to those in summertime, each dominated by the highs extended from the stationary air masses over the Central Siberia and the North Pacific ocean. The migratory highs occur largely in spring and autumn while transferring from the wintertime patterns to summertime patterns, or vice versa. Recently, the occurrence frequency of the highs extended from the North Pacific is on the decrease and while the wintertime pressure patterns occur frequently in spring and autumn, the occurrence frequency of the pressure patterns with trough is on the increase and the migratory highs occur in nearly all seasons.

• Journal of the Korean Geographical Society
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• v.49 no.1
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• pp.32-44
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• 2014

This study aimed to analyze the characteristic of the distribution of minimum temperature during January in the central region of South Korea and to investigate causes for the occurrence of extreme minimum temperature in Cheorwon. January temperature distribution data which were collected from 25 weather stations in central area from 1991 to 2010 were investigated, and the difference of temperature between Cheorwon and the other stations in central region, such as Chuncheon, Hongcheon, Bonghwa, Daegwallyoung, Wonju and Jecheon were analyzed by the type of atmospheric pressure system. Daily mean temperature and mean of daily minimum temperature appear to be low at Cheorwon and at the sites in high altitudes, but the frequency of extreme cold wave such as below $-15^{\circ}C$ is also noticeable in Cheorwon. When the Siberian High has expanded and migratory anticyclone has moved onto the north of the Korean Peninsula, the temperature at Cheorwon is relatively low. Furthermore it shows a lesser difference between Cheorwon and the compared stations when the migratory anticyclone affected the area, even at basin like Bonghwa, Jecheon more lower than Cheorwon.