• Atmosphere
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• v.23 no.2
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• pp.205-220
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• 2013

Upper ocean response to typhoon Ewiniar (0603) and its impact on the following typhoon Bilis (0604) are investigated using observational data and numerical experiments. Data used in this study are obtained from the Ieodo Ocean Research Station (IORS), ARGO, and satellite. Numerical simulations are conducted using 3-dimensional Princeton Ocean Model. Results show that when Ewiniar passes over the western North Pacific, unique oceanic responses are found at two places, One is in East China Sea near Taiwan and another is in the vicinity of IORS. The latter are characterized by a strong sea surface cooling (SSC), $6^{\circ}C$ and $11^{\circ}C$ in simulation and observation, under the condition of typhoon with a fast translation speed (8m $s^{-1}$) and lowering intensity (970 hPa). The record-breaking strong SSC is caused by the Yellow Sea Bottom Cold Water, which produces a strong vertical temperature gradient within a shallow depth of Yellow Sea. The former are also characterized by a strong SSC, $7.5^{\circ}C$ in simulation, with a additional cooling of $4.5^{\circ}C$ after a storm's passage mainly due to enhanced and maintained upwelling process by the resonance coupling of storm translation speed and the gravest mode internal wave phase speed. The numerical simulation reveals that the Ewiniar produced a unfavorable upper-ocean thermal condition, which eventually inhibited the intensification of the following typhoon Bilis. Statistics show that 9% of the typhoons in western North Pacific are influenced by cold wakes produced by a proceeding typhoon. These overall results demonstrate that upper ocean response to a typhoon even after the passage is also important factor to be considered for an accurate intensity prediction of a following typhoon with similar track.

• Atmosphere
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• v.26 no.1
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• pp.59-72
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• 2016

The comparison of prediction errors in geopotential height, temperature, and precipitation forecasts is made quantitatively to evaluate medium-range forecast skills between Global Seasonal Forecasting System version 5 (GloSea5) and Unified Model (UM) in operation by Korea Meteorological Administration during 2014. In addition, the performances in prediction of sea surface temperature anomaly in NINO3.4 region, Madden and Julian Oscillation (MJO) index, and tropical storms in western north Pacific are evaluated. The result of evaluations appears that the forecast skill of UM with lower values of root-mean square error is generally superior to GloSea5 during forecast periods (0 to 12 days). The forecast error tends to increase rapidly in GloSea5 during the first half of the forecast period, and then it shows down so that the skill difference between UM and GloSea5 becomes negligible as the forecast time increases. Precipitation forecast of GloSea5 is not as bad as expected and the skill is comparable to that of UM during 10-day forecasts. Especially, in predictions of sea surface temperature in NINO3.4 region, MJO index, and tropical storms in western Pacific, GloSea5 shows similar or better performance than UM. Throughout comparison of forecast skills for main meteorological elements and weather extremes during medium-range, the effects of initial and model errors in atmosphere-ocean coupled model are verified and it is suggested that GloSea5 is useful system for not only seasonal forecasts but also short- and medium-range forecasts.

• Journal of Ocean Engineering and Technology
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• v.16 no.5
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• pp.15-20
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• 2002

In this research, the finite difference lattice Boltzmann method(FDLBM) is used to analyze gravity currents in the lock exchange configuration that occur in many natural and man-made situations. At a lock those are seen when a gate is suddenly opened, and, in the atmosphere, when the thunderstorm outflows make a cold front. At estuaries in the ocean, the phenomenon is found between fresh water from a river and salt water in the sea. Since such interesting phenomena were recognized, pioneers have challenged to make them clear by conducing both experiments and analysis. Most of them were about the currents of liquid or Boussinesq fluids, which are assumed as incompressible. Otherwise, the difference in density of two fluids is small. The finite difference lattice Boltzmann method has been a powerful tool to simulate the flow of compressible fluids. Also, numerical predictions using FDLBM to clarify the gravity currents of compressible fluids exhibit all features, but typically observed in experimental flows near the gravity current head, including the lobe-and-cleft structure at the leading edge.

• Atmosphere
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• v.26 no.4
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• pp.687-696
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• 2016

The western North Pacific subtropical high (WNPSH) in boreal summer has interannual and interdecadal variability, which affects East Asian summer monsoon variability. In particular, it is well known that the intensity of WNPSH is reversely related to that of summer monsoon in North East Asia in association with Pacific Japan (PJ)-like pattern. Many coupled climate models weakly simulate this large-scale teleconnection pattern and also exhibit the diverse variability of WNPSH. This study discusses the inter-model differences of WNPSH simulated by different climate models, which participate in the Coupled Model Intercomparison Project phase 5 (CMIP5). In comparing with reanalysis observation, the 29 CMIP5 models could be assorted into two difference groups in terms of interannual variability of WNPSH. This study also discusses the dynamical or thermodynamics factors for the differences of two groups of the CMIP5 climate models. As results, the regressed precipitation in well-simulating group onto the Nino3.4 index ($5^{\circ}N-5^{\circ}S$, $170^{\circ}W-120^{\circ}W$) is stronger than that in poorly-simulating group. We suggest that this difference of two groups of the CMIP5 climate models would have an effect on simulating the interannual variability of WNPSH.

• Journal of the Korean Geotechnical Society
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• v.37 no.1
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• pp.5-15
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• 2021

The areas consisting of frost susceptible soils in cold regions, such as the Arctic area, have problems of frost heave and thaw settlement due to the seasonal air temperature changes and internal temperature of installed structures. Ground stabilization methods for preventing frost heave and thaw settlement of frost susceptible soils include trenching, backfilling and thermo-syphon. The thermo-syphon is the method in which refrigerant can control the ground temperature by transferring the ground temperature to atmosphere in the from of two-phase flow through the heat circulation of the internal refrigerant. This numerical study applied the function of these thermo-syphon as the boundary condition through user-subroutine coding inside ABAQUS and compared and analyzed the temperature results of laboratory experiments.

• Journal of Radiation Industry
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• v.8 no.2
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• pp.123-132
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• 2014

After the nuclear accident of the Fukushima Dai-ichi Nuclear Power Plants (FDNPPs) on 11 March 2011, a large amount of radioactive materials has been released into the atmosphere and the ocean. A compartment model is used to evaluate the circulation characteristics and the spatiotemporal concentration distributions of radionuclides in the ocean. In the comparison with observed concentrations of $^{137}Cs$ in seawater, calculated concentrations by the compartment model were well agreed with them. On the basis of these results, we performed evaluation of the effective dose and the cancer risk. In the early stage of the accident, the effective doses from ingestion of the seafood near the Fukushima region were much higher than 1 mSv which is the value of the annual effective dose limit to individual recommended by the International Commission on Radiological Protection (ICRP). However, the effective doses by ingestion of the seafood decreased below 1 mSv as distance from the FDNPPs increased and time passed. In addition, it was estimated that the cancer risks by intake of the contaminated marine products were less than natural occurrence probability of cancer. Consequently, it was inferred that the health risk due to the $^{137}Cs$ was low after since mid-term period of the accident.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.108.1-108.1
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• 2012

Previously we introduced ray-tracing based 3D optical earth system model for specular and scattering properties of all components of the system (i.e. clear-sky atmosphere, land surfaces and an ocean surface). In this study, we enhanced 3-dimensional atmospheric structure with vertical atmospheric profiles for multiple layer and cloud layers using Lambertian and Mie theory. Then the phase dependent disk averaged spectra are calculated. The main results, simulated phase dependent disk averaged spectra and light curves, are compared with the 7 bands(300~1000nm) light curves data of the Earth obtained from High Resolution Instrument(HRI) in Deep Impact spacecraft during Earth flyby in 2008. We note that the results are comparable with the observation.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.138-142
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• 2005

The change of precipitation and temperature due to the global. warming eventually caused the variation of water availability in terms of potential evapotranspiration, soil moisture, and runoff. In this reason national long-term water resource planning should be considered the effect of climate change. Study of AOGCM-based scenario to proposed the plausible future states of the climate system has become increasingly important for hydrological impact assessment. Future climate changes over East Asia are projected from the coupled atmosphere-ocean general circulation model (AOGCM) simulations based on Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 and B2 scenarios using multi-model ensembles (MMEs) method (Min et al. 2004). MME method is used to reduce the uncertainty of individual models. However, the uncertainty increases are larger over the small area than the large area. It is demonstrated that the temperature increases is larger over continental area than oceanic area in the 21st century.

• Atmosphere
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• v.24 no.3
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• pp.403-417
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• 2014

Future changes in seasonal mean temperature and precipitation over East Asia under anthropogenic global warming are investigated by comparing the historical run for 1979~2005 and the Representative Concentration Pathway (RCP) 4.5 run for 2006~2100 with 20 coupled models which participated in the phase five of Coupled Model Inter-comparison Project (CMIP5). Although an increase in future temperature over the East Asian monsoon region has been commonly accepted, the prediction of future precipitation under global warming still has considerable uncertainties with a large inter-model spread. Thus, we select best five models, based on the evaluation of models' performance in present climate for boreal summer and winter seasons, to reduce uncertainties in future projection. Overall, the CMIP5 models better simulate climatological temperature and precipitation over East Asia than the phase 3 of CMIP and the five best models' multi-model ensemble (B5MME) has better performance than all 20 models' multi-model ensemble (MME). Under anthropogenic global warming, significant increases are expected in both temperature and land-ocean thermal contrast over the entire East Asia region during both seasons for near and long term future. The contrast of future precipitation in winter between land and ocean will decrease over East Asia whereas that in summer particularly over the Korean Peninsula, associated with the Changma, will increase. Taking into account model validation and uncertainty estimation, this study has made an effort on providing a more reliable range of future change for temperature and precipitation particularly over the Korean Peninsula than previous studies.

• Journal of the Korean earth science society
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• v.27 no.1
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• pp.61-72
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• 2006

Numerical studies on the influence of interaction between atmosphere and ocean on the variation of Karman vortex at the lee side of Jeju Island were carried out. Karman vortex tends to be occurred at limited height associated with Hanla mountain. And we can find clear Karman vortex at 900 hPa height in this study. One big vortex cell occurred at lee side of Jeju Island in the begging stage of its development and the cell was divided into three small cells as time goes by. And the strength and lifetime of small vortexes depend on the distribution of SST (Sea Surface Temperature). Weak gradient of SST makes long-lasting Karman vortex but produces weak potential vorticity at lee side of Jeju-do in comparison with the vortex under strong SST gradient. Strong SST gradient also increases not only the mixing depth but also the mixing ratio at lower level of troposphere. And the increased atmospheric mixing decreases the mechanical forcing due to isolated topography. Then the strength of Karman vortex at the lee side of Jeju Island becomes weak under strong gradient of SST. Thus the evolution of Karman vortex is closely related to distribution of SST around the isolated island.