• Journal of the Korean earth science society
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• v.40 no.6
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• pp.584-598
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• 2019

In this study, the effects of air-sea interactions on precipitation over the Seoul-Gyeonggi region of the Korean Peninsula from 28 to 30 August 2018, were analyzed using a Regional atmosphere-ocean Coupled Model (RCM). In the RCM, a WRF (Weather Research Forecasts) was used as the atmosphere model whereas ROMS (Regional Oceanic Modeling System) was used as the ocean model. In a Regional Single atmosphere Model (RSM), only the WRF model was used. In addition, the sea surface temperature data of ECMWF Reanalysis Interim was used as low boundary data. Compared with the observational data, the RCM considering the effect of air-sea interaction represented that the spatial correlations were 0.6 and 0.84, respectively, for the precipitation and the Yellow Sea surface temperature in the Seoul-Gyeonggi area, which was higher than the RSM. whereas the mean bias error (MBE) was -2.32 and -0.62, respectively, which was lower than the RSM. The air-sea interaction effect, analyzed by equivalent potential temperature, SST, dynamic convergence fields, induced the change of SST in the Yellow Sea. In addition, the changed SST caused the difference in thermal instability and kinematic convergence in the lower atmosphere. The thermal instability and convergence over the Seoul-Gyeonggi region induced upward motion, and consequently, the precipitation in the RCM was similar to the spatial distribution of the observed data compared to the precipitation in the RSM. Although various case studies and climatic analyses are needed to clearly understand the effects of complex air-sea interaction, this study results provide evidence for the importance of the air-sea interaction in predicting precipitation in the Seoul-Gyeonggi region.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.97-97
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• 2016

가뭄은 홍수와 더불어 매우 심각한 자연재해이며, 그 특성상 광역적이고 장기간 발생함에 따라 구체적인 발생시점, 규모, 범위 등을 규명하기가 어렵다. 다만, 적시에 경보해야 하는 홍수와 달리 진행속도가 느리고 시간적으로 대처할 여유가 있어 진행중 일지라도 초기에 감지한다면 그 피해를 최소화할 수 있다. 미국 등 수문기상 선진국에서는 수문기상 장기예보자료를 활용한 가뭄전망정보 생산 및 제공하고 있으며, 활용성을 검증한바 있다. 국내의 경우 기상청에서는 대기-해양-해빙 모델을 접합한 GloSea5 (Global Seasonal forecasting system version 5) 모델을 도입하였으며, 가뭄예보를 목적으로 장기예보자료 기반의 가뭄전망정보 생산체계를 구축한 바 있다(기상청, 2012; 손경환 등, 2015). 본 연구에서는 장기예보자료 기반의 수문기상 전망정보를 이용하여 2014-15년 가뭄사례에 대한 가뭄감시 및 전망정보를 생산 및 평가하였다. 수문기상전망 정보는 기상청 현업예보 모델인 GloSea5와 지면모델을 이용하여 생산하였으며, 관측자료와 수문전망정보 기반의 가뭄지수를 산정하였다. 매스컴 및 언론 보도 자료부터 2014-15년 가뭄에 대한 행정구역별 피해사례를 수집하였으며, 이를 기반으로 시계열, 지역별 및 통계적(CC, RMSE) 분석을 이용하여 선행시간별 정확도를 평가하였다. 1개월 및 2개월 전망정보의 정확도가 높음을 확인하였으며, 가뭄심도가 심각한 시기의 가뭄상황을 적절히 재현하는 것으로 나타났다.

• Korean Journal of Remote Sensing
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• v.36 no.6_3
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• pp.1643-1652
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• 2020

To investigate the characteristics of detailed flows in a building-congested district, we coupled a computation fluid dynamics (CFD) model to the local data assimilation and prediction system (LDAPS), a current operational numerical weather prediction model of the Korea Meteorological Administration. For realistic numerical simulations, we used the meteorological variables such as wind speeds and directions and potential temperatures predicted by LDAPS as the initial and boundary conditions of the CFD model. We trilinearly interpolated the horizontal wind components of LDAPS to provide the initial and boudnary wind velocities to the CFD model. The trilinearly interpolated potential temperatures of LDAPS is converted to temperatures at each grid point of the CFD model. We linearly interpolated the horizontal wind components of LDAPS to provide the initial and boundary wind velocities to the CFD model. The linearly interpolated potential temperatures of LDAPS are converted to temperatures at each grid point of the CFD model. We validated the simulated wind speeds and directions against those measured at the PKNU-SONIC station. The LDAPS-CFD model reproduced similar wind directions and wind speeds measured at the PKNU-SONIC station. At 07 LST on 22 June 2020, the inflow was east-north-easterly. Flow distortion by buildings resulted in the east-south-easterly at the PKNU-SONIC station, which was the similar wind direction to the measured one. At 19 LST when the inflow was southeasterly, the LDAPS-CFD model simulated southeasterly (similar to the measured wind direction) at the PKNU-SONIC station.

• Journal of Satellite, Information and Communications
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• v.1 no.2
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• pp.63-70
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• 2006

This paper presents the results of Ka band qualification model multiplexers for COMS Payload to be launched in 2008. These are the input and output multiplexers of the satellite transponder to use available frequency resources effectively and the diplexer of the satellite antenna to use the same reflector for both transmitting and receiving frequency bands, respectively. The input multiplexer with four frequency channels has four(4) independent channel filters which consist of an 8-pole elliptic band-pass filter for high frequency selectivity and a 2-pole equalizer for group delay equalization. For low insertion loss, mass and volume reduction, manifold type os employed for output multiplexer. E-plane T-junction is used for either splitting or combining a frequency band into two sub-bands. Asymmetric inductive irises are used to tune the receiving filter easily. The electrical performance and environmental test such as vibration test, mechanical shock test, thermal vacuum test and EMC test are performed and the results of all qualification model multiplexers are compliant to the requirement of each multiplexer. Followed by this qualification, the flight model equipment will be developed.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.40-40
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• 2017

최근 2014년 마른장마의 영향으로 중부 지방에 가뭄이 발생하였으며, 장마철 강수부족은 2015년까지 영향을 미친바 있다. 이로 인해 소양강 댐은 역대 최저수위를 기록하였으며, 일부 지역에서는 제한급수, 농업용수 부족 등의 피해가 발생하였다. 일반적으로 가뭄은 발생순서에 따라 기상학적, 농업적, 수문학적 가뭄 등으로 분류하고 있다 (Wilhite and Grantz, 1985). 기상학적 가뭄은 농업 및 수문학적 가뭄에 영향을 미치는 가뭄의 시작 단계를 의미하며, 가뭄을 판단하는데 있어 중요한 요소라 할 수 있다. 기상학적 가뭄을 정량적으로 판단하기 위해 SPI, PDSI, PN 등이 활용되고 있으며, 특히 강수량 기반의 SPI는 계산과정이 쉽고, 다양한 지속시간(3, 6, 9, 12개월 등)에 따라 가뭄을 객관적으로 판단할 수 있어 가장 활발하게 이용되고 있다(Mckee et al., 1993). 최근 기상청은 대기와 해양-해빙 모델을 접합한 GloSea5의 장기예보자료를 활용하여 월 내지 계절 가뭄전망을 위한 기상학적 가뭄지수를 현업에 활용하고 있다. 다만 국내에서는 주로 단기가뭄(1~3개월)이 빈번하게 발생함에 따라 짧은 예보선행시간을 갖는 가뭄전망에 대한 평가에 집중되어 왔다. 2014, 15년에는 이례적으로 2년 연속 가뭄이 지속된바 있으며, 장기가뭄(3개월 이상)에 대한 전망정보의 필요성이 증가하고 있다. 본 연구에서는 장기예보자료 기반의 기상학적 가뭄전망정보를 산정하고, 2015년 가뭄을 대상으로 활용성을 평가하였다. 이를 위해 ASOS 59개 지점의 관측강수량, GloSea5의 미래예측(Foreacst) 및 과거재현(Hindcast) 자료를 활용하였으며, 다양한 지속시간(3, 6, 9, 12개월)에 대한 SPI를 산정하였다. 또한 예보선행시간(1~6개월)에 따른 SPI와 관측자료 기반의 SPI 간의 통계적 분석(상관계수, 평균제곱근오차)을 수행하여 전망정보의 정확도를 평가하였다.

• Korean Journal of Remote Sensing
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• v.36 no.6_3
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• pp.1653-1667
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• 2020

In this study, we coupled a computation fluid dynamics (CFD) model to the local data assimilation and prediction system (LDAPS), a current operational numerical weather prediction model of the Korea Meteorological Administration. We investigated the characteristics of fine particulate matter (PM2.5) distributions in a building-congested district. To analyze the effects of road emission on the PM2.5 concentrations, we calculated road emissions based on the monthly, daily, and hourly emission factors and the total amount of PM2.5 emissions established from the Clean Air Policy Support System (CAPSS) of the Ministry of Environment. We validated the simulated PM2.5 concentrations against those measured at the PKNU-AQ Sensor stations. In the cases of no road emission, the LDAPS-CFD model underestimated the PM2.5 concentrations measured at the PKNU-AQ Sensor stations. The LDAPS-CFD model improved the PM2.5 concentration predictions by considering road emission. At 07 and 19 LST on 22 June 2020, the southerly wind was dominant at the target area. The PM2.5 distribution at 07 LST were similar to that at 19 LST. The simulated PM2.5 concentrations were significantly affected by the road emissions at the roadside but not significantly at the building roof. In the road-emission case, the PM2.5 concentration was high at the north (wind speeds were weak) and west roads (a long street canyon). The PM2.5 concentration was low in the east road where the building density was relatively low.

• Journal of the Korean earth science society
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• v.43 no.6
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• pp.691-711
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• 2022

The state-of-the-art Earth system model as a virtual Earth is required for studies of current and future climate change or climate crises. This complex numerical model can account for almost all human activities and natural phenomena affecting the atmosphere of Earth. The Unified Model (UM) from the United Kingdom Meteorological Office (UK Met Office) is among the best Earth system models as a scientific tool for studying the atmosphere. However, owing to the expansive numerical integration cost and substantial output size required to maintain the UM, individual research groups have had to rely only on supercomputers. The limitations of computer resources, especially the computer environment being blocked from outside network connections, reduce the efficiency and effectiveness of conducting research using the model, as well as improving the component codes. Therefore, this study has presented detailed guidance for installing a new version of the UM on high-performance parallel computers (Linux clusters) owned by individual researchers, which would help researchers to easily work with the UM. The numerical integration performance of the UM on Linux clusters was also evaluated for two different model resolutions, namely N96L85 (1.875° ×1.25° with 85 vertical levels up to 85 km) and N48L70 (3.75° ×2.5° with 70 vertical levels up to 80 km). The one-month integration times using 256 cores for the AMIP and CMIP simulations of N96L85 resolution were 169 and 205 min, respectively. The one-month integration time for an N48L70 AMIP run using 252 cores was 33 min. Simulated results on 2-m surface temperature and precipitation intensity were compared with ERA5 re-analysis data. The spatial distributions of the simulated results were qualitatively compared to those of ERA5 in terms of spatial distribution, despite the quantitative differences caused by different resolutions and atmosphere-ocean coupling. In conclusion, this study has confirmed that UM can be successfully installed and used in high-performance Linux clusters.