• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.2
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• pp.79-93
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• 2015

Three-dimensional structures of large ocean rings in the Gulf Stream region are investigated using the HYbrid Coordinate Ocean Model (HYCOM). Numerically simulated flow structures around four selected cyclonic and anticyclonic rings are compared with two different horizontal resolutions: $1/12^{\circ}$ and $1/48^{\circ}$. The vertical distributions of Lagrangian Coherent Structures (LCSs) are analyzed using Finite Size Lyapunov Exponent (FSLE) and Okubo-Weiss parameters (OW). Curtain-shaped FSLE ridges are found in all four rings with extensions of surface ridges throughout the water columns, indicating that horizontal stirring is dominant over vertical motions. Near the high-resolution rings, many small-scale flow structures with size O(1~10) km are observed while these features are rarely found near the low-resolution rings. These small-scale structures affect the flow pattern around the rings as flow particles move more randomly in the high-resolution models. The dispersion rates are also affected by these small-scale structures as the relative horizontal dispersion coefficients are larger for the high-resolution models. The absolute vertical dispersion rates are, however, lower for the high-resolution models, because the particles tend to move along inclined eddy orbits when the resolution is low and this increases the magnitude of absolute vertical dispersion. Since relative vertical dispersion can reduce this effect from the orbital trajectories of particles, it gives a more reasonable magnitude range than absolute dispersion, and so is recommended in estimating vertical dispersion rates.

• Atmosphere
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• v.16 no.1
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• pp.33-48
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• 2006

A classification of snowfall type based on development mechanism is proposed using previous snowfall studies, operational experiences, etc. Five types are proposed: snowfall caused by 1) airmass transformation (AT type), 2) terrain effects in a situation of expanding Siberian High (TE type), 3) precipitation systems associated with extratropical cyclones (EC type), 4) indirect effects of extratropical cyclones passing over the sea to the south of the Korean peninsula (ECS type), and 5) combined effects of TE and ECS types (COM type). Snowfall events during 1981-2001 are classified according to the 5 types mentioned above. For this, 118 events, with at least one station with daily snowfall depth greater than 20 cm, are selected. For the classification, synoptic weather charts, satellite images, and precipitation data are used. For TE and COM types, local sea-level pressure chart is also used to confirm the presence of condition for TE type (this is done for events in 1990 and thereafter). The classification shows that 109 out of 118 events can be classified as one of the 5 types. In the remaining 8 events, heavy snowfall occurred only in Ullung Island. Its occurrence may be due to one or more of the following mechanism: airmass transformation, mesoscale cyclones and/or mesoscale convergence over the East Sea, etc. Each type shows different characteristics in location of snowfall and composition of precipitation (i.e., dry snow, rain, and mixed precipitation). The AT-type snowfall occurs mostly in the west coast, Jeju and Ullung Islands whereas the TE-type snowfall occurs in the East coast especially over the Young Dong area. The ECS-type snowfall occurs mostly over the southern part of the peninsula and some east cost area (sometimes, whole south Korea depending on the location of cyclones). The EC- and COM-type snowfalls occur in wider area, often whole south Korea. Precipitation composition also varies with the type. The AT-type has a snow ratio (SR) higher than the mean value. The TE- and EC-type have SR similar to the mean. The ECS- and COM-type have SR values smaller than the mean. Generally the SR values at high latitude and mountainous areas are higher than those at the other areas. The SR value informs the characteristics of the precipitation composition. An SR value larger than 10 means that all precipitation is composed of snow whereas a zero SR value means that all precipitation is composed of rain.

• Journal of the Korean earth science society
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• v.30 no.6
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• pp.709-720
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• 2009

Field observation and numerical experiments were conducted to understand the impact of water retention pavement on the surface heat budget and on the regional circulation. The numerical model applied in this study is the atmospheric dynamic model Local Circulation Model (LCM) with two dimensional grid system, and a field observation was carried out under the clear sky and calm conditions of the weather on 19 July 2007. In the field observation, the maximum value of surface temperature on pavement covered with water retention material reached the $41.2^{\circ}C$ at 1430 LST and the values was lower for $16.1^{\circ}C$ than that of asphalt without the material. The Case BET03 assumed to be 0.3 for the surface evaporation efficiency was in good agreement with the observation and its sensible and latent heat fluxes were numerically estimated to be 229 and 227 $W/m^2$, respectively. Results of the numerical experiments demonstrated that the water retention pavement tends to induce the increase of latent heat flux associated with the lower surface temperature and mixing height during the daytime. Discontinuity of latent heat caused by the water retention pavement also tends to promote the development of mesoscale circulation called as land-land breeze or country breeze.

• Journal of the Korean earth science society
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• v.30 no.4
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• pp.464-477
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• 2009

In this study, we examined the patterns of local circulation over the Daechung lake area through the numerical experiment designed to investigate the impact of lake on the local circulation. The results of numerical experiment showed that the surface temperature predicted by WRF model was lower than the observation, while the wind speed was stronger than the observation. The local circulation over the lake area was characterized by a lake breeze induced by a horizontal thermal contrast between the lake surface and the Surrounding land. At Daecheong Lake, a lake breeze formed at 09 LST and dissipated at 18 LST, with maximum intensity at 15 LST. The vertical extent of the simulated circulation was about 1,200 m. The specific humidity increased as the humid air above the lake moved landward due to the daytime circulation of the lake breeze. The numerical experiments of sensitivity to existence of the lake showed that the simulated surface temperature decreased in the experiment with the lake. Wind speed was more intense around the lake area when the actual land use was substituted by grassland land use. The results of numerical experiments suggest that the lake-induced lake breeze circulation has an effect on the meteorology of planetary boundary layer around the lake.

• 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.

• Korean Journal of Remote Sensing
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• v.20 no.4
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• pp.245-252
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• 2004

The mechanism of cold core eddy formation was investigated using boundary conditions between the East China coastal cold water and the Kuroshio Warm Current, wind data related to the monsoon which was measured by QuikSCAT, and the bottom topography of the East China Sea. When winds blow from the southeast at an intensity comparable to that in the winter period in 1999 and 2003, the warm Kuroshio and Tsushima Current became stronger, and temperatures were considerably higher than those of the extended cold water of the coast of the East China. At that time, the cold water was captured by warm water from the Kuroshio and the Tsushima Current. This facilitated the formation of mesoscale cold core eddies with diameter of 150km in the East China Sea in May, 1999 and February, 2003. The cold core eddy which was detected by NOAA, SeaWiFS and QuikSCAT satellites. The East China Sea is considered to be important not only as a good fishing ground but also nursery and spawning area for many kinds of fishes. Therefore, it would be worth studying spatio-temporal variations of the cold core eddy in the environmental conditions of the northwestern East China Sea using systematic remote sensing techniques.

• Journal of Environmental Science International
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• v.24 no.5
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• pp.601-613
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• 2015

On the study of the characteristics and life cycle of mesoscale convective band in type of airmass that occurred in the Honam area from June to September for only 4 years in the period of 2009~2012, 10 examples based on the amount of rainfall with AWS 24 hours/60 minutes rainfalls, Mt. Osung radar 1.5 km CAPPI/X-SECT images and KLAPS data for convective band with heavy rainfall event were selected. There were analyzed and classified by using the convective band with heavy rainfall occurred along the convergence line of sea wind in the form of individual multi-cellular cell and moving direction of convective band appeared in a variety of patterns; toward southwestern (2 cases), northeastern (4 cases), congesting (2 cases), and changing its moving direction (2 cases). The case study dated of the 17th Aug. 2012 was chosen and implemented by sequentially different evolution of its shape along the convergence line of sea wind cell and moving direction of convective band as equivalent potential temperatures at the lower layer have increased to the upper layer 500 hPa, that the individual cells were developed vertically and horizontally through their merger, but owing to divergence caused by weakened rainfall and descending air current, the growth of new cell was inhibited resulting in dissipation of convective cells.

• Journal of Environmental Science International
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• v.11 no.6
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• pp.497-506
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• 2002

A Photochemical-Trajectory model was used to understand the production of ozone in the atmospheric boundary layer. This model was composed of the trajectory and the photochemical models. To calculate trajectories of air parcels, winds were obtained from the three-dimensional nonhydrostatic mesoscale model (PSU/NCAR MM5V2), and the results were interpolated into constant height surfaces. Numerical integration in the trajectory model was performed by the Runge-Kutta method. The photochemical model consisted of chemical reactions and photodissociation processes. Chemical equations were integrated by the semi-implicit Bulirsch-Stoer method. We performed our experiments from 21 July to 23 July 1994 during the summer time for Seoul area. During the time of maximum ozone concentration in Seoul, four trajectories of air parcels which traveled from Inchon to Seoul were selected. Ozone concentrations estimated by two models are compared with observed one in Seoul area and the photochemical-trajectory model is better fitted than pure photochemical model. During the selected period, high ozone concentrations in Seoul area were more influenced by transferred pollutants from Inchon than emitted pollutants in Seoul.

• Journal of Environmental Science International
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• v.18 no.8
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• pp.847-855
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• 2009

As a part of effort to establish an offshore wind resource assessment system of the Korean Peninsula, a numeric wind simulation using mesoscale climate model MM5 and a spatial distribution of offshore wind extracted from SAR remote-sensing satellite image is compared and analyzed. According to the analyzed results, the numeric wind simulation is found to have wind speed over predication tendency at the coastal sea area. Therefore, it is determined that a high-resolution wind simulation is required for complicated coastal landforms. The two methods are verified as useful ways to identify the spatial distribution of offshore wind by mutual complementation and if the meteor-statistical comparative analysis is performed in the future using adequate number of satellite images, it is expected to derive a general methodology enabling systematic validation and correction of the numeric wind simulation.

• Asian Journal of Atmospheric Environment
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• v.10 no.2
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• pp.80-89
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• 2016

In the complex terrain where local wind systems are formed, accurate understanding of regional wind variability is required for wind resource assessment. In this paper, cluster analysis based on the similarity of time-series wind vector was applied to classify wind regions with similar wind characteristics and the meteorological validity of regionalization method was evaluated. Wind regions in Jeju Island and Busan were classified using the wind resource map of Korea created by a mesoscale numerical weather prediction modeling. The evaluation was performed by comparing wind speed, wind direction, and wind variability of each wind region. Wind characteristics, such as mean wind speed and prevailing wind direction, in the same wind region were similar and wind characteristics in different wind regions were meteor-statistically distinct. It was able to identify a singular wind region at the top area of Mt. Halla using the inconsistency of wind direction variability. Furthermore, it was found that the regionalization results correspond with the topographic features of Jeju Island and Busan, showing the validity.