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Lim, Kyo-Sun Sunny,Lim, Jong-Myung,Lee, Jiwoo,Shin, Hyeyum Hailey Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.1
Wind plays an important role in cases of unexpected radioactive pollutant dispersion, deciding distribution and concentration of the leaked substance. The accurate prediction of wind has been challenging in numerical weather prediction models, especially near the surface because of the complex interaction between turbulent flow and topographic effect. In this study, we investigated the characteristics of atmospheric dispersion of radioactive material (i.e. <sup>137</sup>Cs) according to the simulated boundary layer around the HANARO research nuclear reactor in Korea using the Weather Research and Forecasting (WRF)-Mesoscale Model Interface (MMIF)-California Puff (CALPUFF) model system. We examined the impacts of orographic drag on wind field, stability calculation methods, and planetary boundary layer parameterizations on the dispersion of radioactive material under a radioactive leaking scenario. We found that inclusion of the orographic drag effect in the WRF model improved the wind prediction most significantly over the complex terrain area, leading the model system to estimate the radioactive concentration near the reactor more conservatively. We also emphasized the importance of the stability calculation method and employing the skillful boundary layer parameterization to ensure more accurate low atmospheric conditions, in order to simulate more feasible spatial distribution of the radioactive dispersion in leaking scenarios.
Bae, Soo Ya,Hong, Song-You,Lim, Kyo-Sun Sunny Hindawi Limited 2016 Advances in meteorology Vol.2016 No.-
<P>A method to explicitly calculate the effective radius of hydrometeors in the Weather Research Forecasting (WRF) double-moment 6-class (WDM6) microphysics scheme is designed to tackle the physical inconsistency in cloud properties between the microphysics and radiation processes. At each model time step, the calculated effective radii of hydrometeors from the WDM6 scheme are linked to the Rapid Radiative Transfer Model for GCMs (RRTMG) scheme to consider the cloud effects in radiative flux calculation. This coupling effect of cloud properties between the WDM6 and RRTMG algorithms is examined for a heavy rainfall event in Korea during 25–27 July 2011, and it is compared to the results from the control simulation in which the effective radius is prescribed as a constant value. It is found that the derived radii of hydrometeors in the WDM6 scheme are generally larger than the prescribed values in the RRTMG scheme. Consequently, shortwave fluxes reaching the ground (SWDOWN) are increased over less cloudy regions, showing a better agreement with a satellite image. The overall distribution of the 24-hour accumulated rainfall is not affected but its amount is changed. A spurious rainfall peak over the Yellow Sea is alleviated, whereas the local maximum in the central part of the peninsula is increased.</P>
Han, Ji-Young,Hong, Song-You,Lim, Kyo-Sun Sunny,Han, Jongil AMERICAN METEOROLOGICAL SOCIETY 2016 Monthly weather review Vol.144 No.6
<P>The sensitivity of a cumulus parameterization scheme (CPS) to a representation of precipitation production is examined. To do this, the parameter that determines the fraction of cloud condensate converted to precipitation in the simplified Arakawa-Schubert (SAS) convection scheme is modified following the results from a cloud-resolving simulation. While the original conversion parameter is assumed to be constant, the revised parameter includes a temperature dependency above the freezing level, which leads to less production of frozen precipitating condensate with height. The revised CPS has been evaluated for a heavy rainfall event over Korea as well as medium-range forecasts using the Global/Regional Integrated Model system (GRIMs). The inefficient conversion of cloud condensate to convective precipitation at colder temperatures generally leads to a decrease in precipitation, especially in the category of heavy rainfall. The resultant increase of detrained moisture induces moistening and cooling at the top of clouds. A statistical evaluation of the medium-range forecasts with the revised precipitation conversion parameter shows an overall improvement of the forecast skill in precipitation and large-scale fields, indicating importance of more realistic representation of microphysical processes in CPSs.</P>
Uju Shin,Sang-Hun Park,GyuWon Lee,Kyo-Sun Sunny Lim 한국기상학회 2021 한국기상학회 학술대회 논문집 Vol.2021 No.10
This study aims to evaluate the regional Model for Prediction Across Scales (rMPAS) simulations in the lee side heavy snowfall episodes during the International Collaborative Experiments held at the PyeongChang 2018 Olympics and Winter Paralympic Games (ICE-POP 2018) field campaign against WRF model results and observations. For this purpose, we selected three heavy snowfall episodes during the campaign to perform high-resolution numerical experiments. In this study, we 1) verify the simulated precipitation and synoptic environment of the rMPAS by comparing it with the WRF model and observations; 2) examine the characteristics of the rMPAS’s horizontal momentum advection compared to the 3rd- and 5th-order horizontal advection scheme of the WRF model; and 3) compare the feature of vertical motion in the rMPAS and WRF associated with complex terrain. ⦁Case studies reveal that the rMPAS and WRF models correctly reproduce the heavy snowfalls and their environment in the winter season of the Korean peninsula. Therefore, we could confirm that the rMPAS and WRF models have the capability to predict heavy snowfall in the eastern coastal region of the Korean peninsula. ⦁In all snowfall cases, the WRF model simulates a more robust upward/downward motion near complex terrain compared to the rMPAS results and the Wind Synthesis System using Doppler Measurement (WISSDOM) data. ⦁Even though the third-order scalar horizontal advection is applied in the rMPAS, the kinetic energy spectra of rMPAS are similar to the fifth-order horizontal advection of WRF than the third-order advection scheme in the small scales.