• Atmosphere
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• v.29 no.4
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• pp.429-438
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• 2019

Organic carbon (OC) and elemental carbon (EC) in PM_2.5 were measured with Sunset Laboratory Model-5 Semi-Continuous OC/EC Field Analyzer by NIOSH/TOT method at Anmyeondo Global Atmosphere Watch (GAW) Regional Station (37°32'N, 127°19'E) in July and August, 2017. The mean values of OC and EC were 3.7 ㎍ m^-3 and 0.7 ㎍ m^-3, respectively. During the study period, the concentrations of reactive gases and aerosol compositions were evidently lower than those of other seasons. It is mostly due to meteorological setting of the northeast Asia, where the influence of continental outflow is at its minimum during this season under southwesterly wind. While the diurnal variation of OC and EC were not clear, the concentrations of O₃, CO, NOx, EC, and OC were evidently enhanced under easterly wind at night from 20:00 to 8:00. However, the high concentration of EC was observed concurrently with CO and NOx under northerly wind during 20:00~24:00. It indicates the influence of thermal power plant and industrial facilities, which was recognized as a major emission source during KORUS-AQ campaign. The diurnal variations of pollutants clearly showed the influence of land-sea breeze, in which OC showed good correlation between EC and O₃ in seabreeze. It is estimated to be the recirculation of pollutants in land-sea breeze cycle. This study suggests that in general, Anmyeondo station serves well as a background monitoring station. However, the variation in meteorological condition is so dynamic that it is primary factor to determine the concentrations of secondary species as well as primary pollutants at Anmyeondo station.

• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.91-97
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• 2005

The purpose of this study is to provide basic data for establishment of prevention counterplan against construction accidents in preparation for variation of climate conditions. In order to execution of this study, it was analyzed relations of climate factors and cases of construction accident occurred construction sites. In occurrence of construction accidents inducing death upon variation of Climate factors, precipitation and wind velocity were not related directly to construction accidents inducing death. On the other hand, the more temperature and humidity are high, the more construction accidents inducing death occurred. Especially, when temperature and humidity are above $24^{\circ}C,\;70\%$ respectively, field managers must pay attention to safety management of construction sites.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.302-305
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• 2007

During the CareBeijing campaign in September 2006, Imaging Differential Optical Absorption Spectroscopy (IDOAS) measurements were made over the city of Beijing, China using a spatial resolution of 146 pixels horizontally and 61 pixels vertically, each with a field of view of $0.133^{\circ}$ and $0.072^{\circ}$ in the horizontal and vertical directions, respectively. Using Fraunhofer reference spectra (FRS) for the evaluation of data for two consecutive days, the diurnal variation of $NO_2$ distributions was determined from data measured every single hour from 08:00 until 16:00 on September 9 and 10. Both days presented a fairly clear sky with high visibility. The setup allowed detailed images of the low surface $NO_2$ distribution over Beijing. Images with less than a 30-min temporal resolution showed variation of plume dispersal in both horizontal and vertical directions. An in-situ measurement was also conducted. Results from both instruments are interpreted by considering local emission sources and wind conditions.

• Ocean and Polar Research
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• v.25 no.spc3
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• pp.361-371
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• 2003

The effect of bottom friction on the steady wind-driven circulation in the Yellow Sea and the East China Sea (YSECS) has been studied using a two-dimensional numerical model with and without tidal forcing. Upwind flow experiment in YSECS has also been carried out with a schematic time variation in the wind field. The surface water setup and circulation pattern due to steady wind forcing are found to be very sensitive to the bottom friction. When the effects of tidal currents are neglected, the overall current velocities are overestimated and eddies of various sizes appear, upwind flow is formed within the deep trough of the Yellow Sea, forming a part of the topographic gyre on the side of Korea. When tidal forcing is taken into account, the wind-induced surface elevations are smoothed out due to the strong tide-induced bottom friction, which is aligned almost normal to the wind stresses; weak upwind flow is farmed in the deep trough of the Yellow Sea, west and south of Jeju. Calculation with wind forcing only through a parameterized linear bottom friction produces almost same results from the calculation with $M_2$ tidal forcing and wind forcing using a quadratic bottom friction, supporting Hunter (1975)'s linearization of bottom friction which includes the effect of tidal current, can be applied to the simulation of wind-driven circulation in YSECS. The results show that steady wind forcing is not a dominant factor to the winter-time upwind flow in YSECS. Upwind flow experiment which considers the relaxation of pressure gradient (Huesh et al. 1986) shows that 1) a downwind flow is dominant over the whole YSECS when the northerly wind reaches a maximum speed; 2) a trend of upwind flow near the trough is found during relaxation when the wind abates; 3) a northward flow dominates over the YSECS after the wind stops. The results also show that the upwind flow in the trough of Yellow Sea is forced by a wind-induced longitudinal surface elevation gradient.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.2
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• pp.55-63
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• 2008

We investigated characteristics of temperature variation in urban and suburban areas(e.g., paddy field, upland, park, residential area) and urban heat island(UHI) during winter(December 2005 to February 2006). The daily maximum air temperature was not significantly different between suburban and urban areas, whereas the daily minimum air temperatures were significantly lower in the suburban areas than that in the residential area. The wind speed in the urban park(0.3 m/s) was much lower than that in the paddy fields(2.3 m/s), likely due to an urban canopy layer formed by high buildings. The UHI intensity was represented by differences in daily minimum temperatures between urban residential and paddy field areas. The UHI intensity($4.1^{\circ}C$) in winter was larger than that($2.6^{\circ}C$) in summer. This may be because a stable boundary layer develops in the winter, and thereby this inhibits diffusion of heat from surface.

• Journal of Astronomy and Space Sciences
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• v.30 no.2
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• pp.101-106
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• 2013

The length of solar cycle 23 has been prolonged up to about 13 years. Many studies have speculated that the solar cycle 23/24 minimum will indicate the onset of a grand minimum of solar activity, such as the Maunder Minimum. We check the trends of solar (sunspot number, solar magnetic fields, total solar irradiance, solar radio flux, and frequency of solar X-ray flare), interplanetary (interplanetary magnetic field, solar wind and galactic cosmic ray intensity), and geomagnetic (Ap index) parameters (SIG parameters) during solar cycles 21-24. Most SIG parameters during the period of the solar cycle 23/24 minimum have remarkably low values. Since the 1970s, the space environment has been monitored by ground observatories and satellites. Such prevalently low values of SIG parameters have never been seen. We suggest that these unprecedented conditions of SIG parameters originate from the weakened solar magnetic fields. Meanwhile, the deep 23/24 solar cycle minimum might be the portent of a grand minimum in which the global mean temperature of the lower atmosphere is as low as in the period of Dalton or Maunder minimum.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.2
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• pp.197-204
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• 2018

In the present study, unsteady flow analysis has been conducted to investigate the blade forces and wake flow around a hybrid street-lamp having a vertical-axis small wind turbine and a photovoltaic panel. Uniform velocities of 3, 5 and 7 m/s are applied as inlet boundary condition. Relatively large vortex shedding is formed at the wake region of the photovoltaic panel, which affects the increase of blade torque and wake flow downstream of the wind turbine. It is found that blade force has a good relation to the variation of the angle of attack with the rotation of turbine blades. Variations in the torque on the turbine blade over time create a cyclic fluctuation, which can be a source of turbine vibration and noise. Unsteady fluctuation of blade forces is also analyzed to understand the nature of the vibration of a small wind turbine over time. The detailed flow field inside the turbine blades is analyzed and discussed.

• Wind and Structures
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• v.29 no.1
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• pp.33-41
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• 2019

The interaction of head waves with an infinite row of identical, equally spaced, rectangular breakwaters is investigated in the presence of uneven bottom topography. Using linear water wave theory and matched eigenfunction expansion method, the boundary value problem is transformed into a system of linear algebraic equations which are numerically solved to know the velocity potentials completely. Utilizing this method, reflected and transmitted wave energy are computed for different physical parameters along with the wave field in the vicinity of breakwaters. It is observed that the wave field becomes more complicated when the incoming wavelength becomes smaller than the channel width. A critical ratio of the gap width to the channel width, corresponding to the inflection point of the transmitted energy variation, is identified for which 1/3 of the total energy is transmitted. Similarly, depending on the incident wavelength, there is a critical breakwater width for which a minimum energy is transmitted. Further, the accuracy of the computed results is verified by using the derived energy relation.

• Journal of Astronomy and Space Sciences
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• v.29 no.3
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• pp.259-267
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• 2012

Polar cap potential has long been considered as an indicator for the amount of energy flowing in the magnetosphere-ionosphere system. Thus, the estimation of polar cap potential is important to understand the physical process of the magnetosphere. To estimate the polar cap potential in the Northern Hemisphere, merging electric field by Kan & Lee (1979) is adopted. Relationships between the PC index and calculated merging electric field ($E^*$) are examined during full-time and storm-time periods separately. For this purpose Dst, AL, and PC indices and solar wind data are utilized during the period from 1996-2003. From this linear relationship, polar cap potential (${\Phi}^*$) is estimated using the formula by Doyle & Burke (1983). The values are represented as $58.1{\pm}26.9$ kV for the full-time period and $123.7{\pm}84.1$ kV for a storm-time period separately. Considering that the average value of polar cap potential of Doyle & Burke (1983) is about 47 kV during moderately quiet intervals with the S3-2 measurements, these results are similar to such. The monthly averaged variation of Dst, AL, and PC indices are then compared. The Dst and AL indices show distinct characteristics with peaks during equinoctial season whereas the average PC index according to the month shows higher values in autumn than in spring. The monthly variations of the linear correlation coefficients between solar wind parameters and geomagnetic indices are also examined. The PC-AL linear correlation coefficient is highest, being 0.82 with peaks during the equinoctial season. As with the AL index, the PC index may also prove useful for predicting the intensity of an auroral substorm. Generally, the linear correlation coefficients are shown low in summer due to conductance differences and other factors. To assess the role of the PC index during the recovery phase of a storm, the relation between the cumulative PC index and the duration is examined. Although the correlation coefficient lowers with the storm size, it is clear that the average correlation coefficient is high. There is a tendency that duration of the recovery phase is longer as the PC index increases.

• Asian Journal of Atmospheric Environment
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• v.4 no.2
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• pp.89-96
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• 2010

To identify the domains that have the greatest impacts on air quality at the surface, both the upwind and downwind areas of Seoul were determined by season using refined wind fields. Four consecutive days were selected as the study period typical of each season. The mesoscale meteorology of the study period was reproduced by using the MM5 prognostic meteorological model (PSU/NCAR Mesoscale Model) with horizontally nested grids. The gridded meteorological field, which was used on the study area of $242\;km{\times}226\;km$ with grid spacing of 2 km, was generated by using the CALMET diagnostic meteorological model. Upwind and downwind areas of Seoul were determined by calculating 24-hour backward and forward air parcel trajectories, respectively, with u, v, and w velocity vectors. The results showed that the upwind and downwind areas were extended far to the northwest and the southeast as a result of high wind speeds in the spring and winter, while they were restricted on the fringe of Seoul in the summer and fall.