• Korean Journal of Ichthyology
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• v.18 no.4
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• pp.319-328
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• 2006

The relationships among long-term climate variation at the southern part of the Korean peninsula, oceanic conditions in the South Sea, Korea, and variation in the winter catch of yellowtail (Seriola quinqueradiata) were analyzed using 32 years of time-series data from 1971~2002. In the early 1990s, winter climatic conditions at the southern part of Korean peninsula shifted from a cool to a warm regime with higher air temperature, relative weak wind speed, and lower relative humidity. Also, the winter water temperature at 50 m depth became consistently higher in the South Sea. The annual winter catch of yellowtail in the South Sea increased dramatically in the early 1990s, as did that of anchovy, which is the major food organism for yellowtail. From the results of correlation analysis, we found that the winter catch of yellowtail was more closely related to the increasing of air temperature, water temperature and anchovy catch.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.30.2-30.2
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• 2010

Numerous operational anomalies and satellite failures have been reported since the beginnings of the "space age". Space weather effects on modern spacecraft systems have been emphasized more and more as increasing their complexity and capability. Energetic particles potentially can destroy and degrade electronic components in satellites. We analyzed the geostationary (GEO) satellite anomalies during 1997-2009 to search possible influences of space weather on the satellite anomalies like power problem, control processor problem, attitude control problem, etc. For this we use particle data from GOES and LANL satellites to investigate space weather effects on the GEO satellites' anomalies depending on Kp index, local time, seasonal variation, and high-energy electron contribution. As results, we obtained following results: (1) there is a good correlation between geomagnetic index(Kp) and anomaly occurrences of the GEO satellite; (2) especially during the solar minimum, occurrence of the satellite anomalies are related to electron flux increase due to high speed solar wind; (3) satellite anomalies occurred more preferentially in the midnight and dawn sector than noon and dusk sector; (4) and the anomalies occurred twice more in Spring and Fall than Summer and Winter; (5) the electron with the lowest energy channel (50-75keV) has the highest correlation (cc=0.758) with the anomalies. High association between the anomalies and the low energy electrons could be understand by the facts that electron fluxes in the spring and fall are stronger than those in the summer and winter, and low-energy electron flux is more concentrated in the dawn sector where the GEO satellite anomalies occurred more frequently than high-energy electron flux. While we could not identify what cause such local time dependences, our results shows that low-energy electrons (~100keV) could be main source of the satellite anomaly, which should be carefully taken into account of operating satellites.

• Atmosphere
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• v.27 no.1
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• pp.1-16
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• 2017

In this study, trends of upper jet stream characteristics (intensity, altitude, latitude, and longitude) over the Asia-North Pacific region during the recent 30 (1979~2008) years were analyzed by using four reanalysis datasets (CFSR, ERA-Int., JRA-55, MERRA). We defined the characteristics of upper jet stream as the averages of mass weighted wind speed, mass-flux weighted altitude, latitude and longitude between 400 and 100 hPa. Due to the vertical averaging of jet stream characteristics, our results reveal a weaker spatial variabilities and trends than previous studies. In general, the four reanalysis datasets show similar jet stream properties (intensity, altitude, latitude and longitude) although the magnitude and trends are slightly different among the reanalysis datasets. The altitude of MERRA is slightly higher than that of others for all seasons. The domain averaged intensity shows a weakening trend except for winter and the altitude of jet stream shows an increasing trend for all seasons. Also, the meridional trend of jet core shows a poleward trend for all seasons but it shows a contrasting trend, poleward trend in the continental area but equatorward trend in the Western Pacific region during summer. The zonal trend of jet core is very weak but a relatively strong westward trend in jet core except for spring and winter. The trends of jet stream characteristics found in this study are thermodynamically consistent with the global warming trends observed in the Asia-Pacific region.

• Korean Journal of Remote Sensing
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• v.34 no.1
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• pp.25-43
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• 2018

The effects of hydro-meteorological and surface variables on the frequency of Asian dust events (FAE) were investigated using ground station and satellite-based data. Present weather codes 7, 8, and 9 derived from surface synoptic observations (SYNOP)were used for counting FAE. Surface wind speed (SWS), air temperature (Ta), relative humidity (RH), and precipitation were analyzed as hydro-meteorological variables for FAE. The Normalized Difference Vegetation Index (NDVI), land surface temperature (LST), and snow cover fraction (SCF) were used to consider the effects of surface variables on FAE. The relationships between FAE and hydro-meteorological variables were analyzed using Z-score and empirical orthogonal function (EOF) analysis. Although all variables expressed the change of FAE, the degrees of expression were different. SWS, LST, and Ta (indices applicable when Z-score was < 0) explained about 63.01, 58.00, and 56.17% of the FAE,respectively. For NDVI, precipitation, and RH, Asian dust events occurred with a frequency of about 55.38, 67.37, and 62.87% when the Z-scores were > 0. EOF analysis for the FAE showed the seasonal cycle, change pattern, and surface influences related to dryness condition for the FAE. The intensity of SWS was the main cause for change of FAE, but surface variables such as LST, SCF, and NDVI also were expressed because wet surface conditions suppress FAE. These results demonstrate that not only SWS and precipitation, but also surface variables, are important and useful precursors for monitoring Asian dust events.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.3
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• pp.103-111
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• 2006

The spray behavior of direct-injection spark-ignition(DISI) engines is crucial for obtaining the required mixture distribution for optimal engine combustion. The spray characteristics of DISI engines are affected by many factors such as piston bowl shape, air flow, ambient temperature, injection pressure and fuel temperature. In this study, the effect of fuel temperature on the spray and combustion characteristics was partially investigated for the wall-guided system. The effect of fuel temperature on the fan spray characteristics was investigated in a steady flow rig embodied in a wind tunnel. The shadowgraphy and direct imaging methods were employed to visualize the spray development at different fuel temperatures. The microscopic characteristics of spray were investigated by the particle size measurements using a phase Doppler anemometry(PDA). The effect of injector temperature on the engine combustion characteristics during cold start and warming-up operating conditions was also investigated. Optical single cylinder DISI engine was used for the test, and the successive flame images captured by high speed camera, engine-out emissions and performance data have been analyzed. This could give the way of forming the stable mixture near the spark plug to achieve the stable combustion of DISI engine.

• Journal of the Korean Solar Energy Society
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• v.30 no.6
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• pp.118-124
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• 2010

In order to develop commercial model of 10kW dish-Stirling solar thermal power system, modification for the exiting facility was taken for a year as a Leading Project in KIER. During the project, solar tracking system, control and monitoring system and high durability reflector were developed and long term operation were performed. The solar tracking system was tested for four months to investigate the degree of precision and adapted to the control system for an actual operation from October in 2009. The sun tracking accuracy of ${\pm}4$ mrad using modified control system was obtained and the system operated successfully during the experimental period. The monitoring system displays engine pressure, electric generation amounts, generator RPM, receiver temperatures, and etc. from Stirling engine and weather data of Direct Normal Irradiation, Horizontal Global Insolation, wind speed & direction, and atmosphere temperature from weather station. According to the operating results in a clear sky day, electric power of 6,890 W was generated at the DNI value of 850 W/$m^2$ and the averaged solar-to-electricity efficiency during a whole day reached to 18.99%. From the overall operating results, linear power generation trend could be observed with increasing DNI value. The solar-to-electricity efficiency achieved to 19% around the DNI value of 700 W/$m^2$ and increased to 20% when the DNI value goes up to 900 W/$m^2$.

• Journal of Environmental Science International
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• v.27 no.7
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• pp.489-497
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• 2018

In this study, the ion index characteristics of small and medium urban land use types were investigated in the city of Chungju. The average temperature for each land use type was in the order: general commercial district ($29.59^{\circ}C$) > general residential district ($28.34^{\circ}C$) > productive green district ($28.31^{\circ}C$). The average relative humidity was in the order: productive green district (70.12%) > general residential district (69.93%) > general commercial district (66.48%). The average wind speed was in the order: productive green district (0.95 m/s) > general commercial district (0.87 m/s) > general residential district (0.54 m/s). Positive and negative ions were investigated to determine the ion index by land use type. The average amount of positive ion generated was in the order: general commercial district ($737ea/cm^3$) > general residential district ($492ea/cm^3$) > productive green district ($445ea/cm^3$). The average negative ion production decreased in the order: productive green district ($930ea/cm^3$) > general residential district ($754ea/cm^3$) > general commercial district ($744ea/cm^3$). The ion index calculated from measured data can be arranged in the order: productive green district (2.09) > general residential district (1.53) > general commercial district (1.01). These results confirm the state of positive and negative ion generation in each land use type. Further, the differences in the ion index by land use type were confirmed. However, a limitation of this study is that simple summer measurements were conducted, and seasonal characteristics were not considered. Therefore, any future investigation and research should consider seasonal variation characteristics.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.159-163
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• 2005

Marine accidents of 70.9% have been caused by small ships less than 100 tons in the past 5 years(1998${\sim}$2002). This is ascribable to the graying and lack in expertise on shipping of small ship operators, and merchant ships are hindered from coastal navigation due to the increase of coastal fishing boats and liners. Currently, ECDIS and GPS Plotters are widely used as navigation equipment providing route information to operators, but it can not give any function of automatic route creation and route explanation, so they are available only experienced operators. Especially, the present situation is that no study is made of the automatic route creation and route explanation using ENC for ECDIS, substitution system of paper chart. In this paper, Navigation Guiding System(NGS) is proposed to generate an optimal route where ENC and GPS data is fusioned including the wind speed and direction of anemometer. The proposed system was testified by a simulation, and its effectiveness was verified.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.05a
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• pp.318-320
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• 2018

When a ship sails on sea, it may be influenced by the environmental disturbance such as wind, wave, sea surface temperature, etc. These affect on the ship's speed, fuel consumption, safety and operating performance. It is necessary to find the optimal weather route of a ship to avoid adverse weather conditions which can put the crews in serious danger or cause structural damage to the vessel, machinery, and equipment. This study introduced how to apply A* algorithm based on sea trial test data for determining the optimal ship routes. The path cost function was modelled as a function of minimum arrival time or minimum energy depending on the time of various environment conditions. The specially modelled path-cost function and the safety constraints were applied to the A* algorithm in order to find the optimal path of the ship. The comparison of ship performances estimated by real sea trial's path and estimated optimal route during the voyage of the ship was investigated. The result of this study can be used to create a schedule to ensure safe operation of the ship with short passage time or minimum energy. In addition, the result of this study can be integrated into an on-board decision supporting expert system and displayed in Electronic Chart Display and Information System (ECDIS) to provide all the useful information to ship master.

• Journal of agriculture & life science
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• v.45 no.4
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• pp.29-35
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• 2011

A forest fire was one of the huge disasters and damaged human lifes and a properties. Therefore, many countries operated forest fire forecasting systems which developed from forest fire records, weather data, fuel models and etc. And many countries also estimated future state of forest fire using a long-term climate forecasting like GCMs and prepared resources for future huge disasters. In this study, we analyzed relationships between forest fire occurrence and meteorological factors (the minimum temperature ($^{\circ}C$), the relative humidity (%), the precipitation (mm), the duration of sunshine (hour) and etc.) for developing a estimating tools, which could forecast forest fire regime under future climate change condition. Results showed that forest fires in this area were mainly occurred when the maximum temperature was $10{\sim}200^{\circ}C$, when the relative humidity was 40~60%, and when the average wind speed was under 2m/s. And forest fires mainly occurred at 2~3 day after rainfall.