Minsu Joh

An Evaluation of the Software System Dependency of a Global Atmospheric Model

AbstractThis study presents the dependency of the simulation results from a global atmospheric numerical model on machines with different hardware and software systems. The global model program (GMP) of the Global/Regional Integrated Model system (GRIMs) is tested on 10 different computer systems having different central processing unit (CPU) architectures or compilers. There exist differences in the results for different compilers, parallel libraries, and optimization levels, primarily a result of the treatment of rounding errors by the different software systems. The system dependency, which is the standard deviation of the 500-hPa geopotential height averaged over the globe, increases with time. However, its fractional tendency, which is the change of the standard deviation relative to the value itself, remains nearly zero with time. In a seasonal prediction framework, the ensemble spread due to the differences in software system is comparable to the ensemble spread due to the differences in initial co...

Future Changes in Surface Runoff over Korea Projected by a Regional Climate Model under A1B Scenario

This study assesses future change of surface runoff due to climate change over Korea using a regional climate model (RCM), namely, the Global/Regional Integrated Model System (GRIMs), Regional Model Program (RMP). The RMP is forced by future climate scenario, namely, A1B of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The RMP satisfactorily reproduces the observed seasonal mean and variation of surface runoff for the current climate simulation. The distribution of monsoonal precipitation-related runoff is adequately captured by the RMP. In the future (2040–2070) simulation, it is shown that the increasing trend of temperature has significant impacts on the intra-annual runoff variation. The variability of runoff is increased in summer; moreover, the strengthened possibility of extreme occurrence is detected in the future climate. This study indicates that future climate projection, including surface runoff and its variability over Korea, can be adequately addressed on the RMP testbed. Furthermore, this study reflects that global warming affects local hydrological cycle by changing major water budget components. This study adduces that the importance of runoff should not be overlooked in regional climate studies, and more elaborate presentation of fresh-water cycle is needed to close hydrological circulation in RCMs.

Climate Change due to the Gradual Increase in Atmospheric CO2: A Climate System Model Sensitivity Study

A numerical experiment investigating climate change due to the gradual increase in atmospheric carbon dioxide (CO2) has been performed with the community climate system model (CCSM) developed by National Center for Atmospheric Research (NCAR). Composed of four independent component models simulating the earth’s atmosphere, ocean, land surface, and sea-ice and one central coupler, the CCSM is used to simulate and understand the earth’s past, present and future climate states. The model experiment consists of a control run with a fixed atmospheric CO2 concentration at a standardized value for 1990 to 2000 (355 ppmv) and a transient run with a gradually increased atmospheric CO2 at the rate of 1% per year. jaThe initial CO2 concentration of the transient run is 355 ppmv. Each run has been performed for 80 simulated years. In this experiment, climate change due to the gradually increased atmospheric CO2 is defined as the difference between the results from the transient and control runs. At the time of CO2 doubling (about year 70), the globally averaged surface air temperature increases by 1.25°C. The surface air temperature increases are more predominant over the higher-latitude land areas than over other areas, especially in boreal winter. With an increase in the surface air temperature, there is a decrease in the diurnal temperature range, with the nighttime minimum temperature increasing more than the daytime maximum temperature. And air temperature shows tropospheric warming and stratospheric cooling causing the strong temperature gradient and polar jet intensifications.

Development and implementation of river‐routing process module in a regional climate model and its evaluation in Korean river basins

This study assessed the potential for river discharge simulation by implementing an online river-routing scheme into the regional climate model (RCM) framework as a unified subroutine module and investigated the sensitivity of simulated river flows in response to changes in spatial resolutions in RCM and river-routing scheme. The river-routing scheme gathers runoff from the RCM and advects them horizontally along the river drainage network. The dynamical downscaling simulations were driven by reanalysis at the boundaries for the period of 2000–2010, using different grid sizes for RCM (50 and 12.5 km) and for river-routing scheme (0.5°, 0.25°, and 0.125°). Simulated river discharge was evaluated throughout the three largest river basins in Korea. The simulation results showed potential for river discharge modeling in the RCM framework. The model generally captured the seasonal and monthly variabilities, and the daily scale peaks. From the resolution sensitivity experiments, it was confirmed that high-resolution RCM enhances the reproducibility of river discharge; however, the lack of sophistication of the current river-routing scheme, which was originally developed for continental and macroscale application, mitigates taking advantage of enhanced resolution in river model. On the basis of our findings and experiences in this study, we revealed several considerable issues for future developments of river simulation in the RCM framework.

Assessment of WRF microphysics schemes in simulation of extreme precipitation events based on microwave radiative signatures

ABSTRACT Passive microwave radiometric signatures are affected by microphysical properties and hydrometeor distributions. Various microphysical properties of hydrometeors assumed in numerical simulations of precipitating clouds cause the different emission and scattering signals. This study compares the radiometric signatures obtained from five microphysics (MP) schemes of the Weather Research and Forecasting (WRF) model during the simulation of eight typhoons with respect to Tropical Rainfall Measuring Mission Microwave Imager observations. The MP schemes include the Thompson (MP8), Morrison two moment (MP10), WRF Double Moment 6 Class (MP16), National Severe Storms Laboratory 2 moment (MP17), and Thompson aerosol-aware (MP28) schemes. The results show that most of the schemes produce insufficient emission/scattering signals from liquid/ice particles over the same rain rate compared to the observations. It was also confirmed that, depending on the schemes, the scattering signals appear to be more variable than the emission signals. In general, MP16 is more frequently identified as the scheme with the smallest biases in both low- and high-frequency channels for individual orbits. However, the results demonstrate that one scheme does not work best in all cases examined here. This suggests that the characteristics assumed in MP schemes should be carefully understood to simulate precipitating clouds. Moreover, comparisons of the radiometric signatures from simulations and observations might be used to understand the uncertainties caused by incorrect assumptions of the microphysical properties of precipitating clouds.

Wind-Induced Water Exchange between Stratified Basins

ABSTRACT Yuk, J.-H.; Aoki, S., and Joh, M., 2016. Wind-induced water exchange between stratified basins. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 188–192. Coconut Creek (Florida), ISSN 0749-0208. Water exchange between Inohanako Estuary and Hamanako Bay, Japan with density stratification is investigated using the field data. The basins are connected by a narrow channel with length 200 m through which waters and nutrients are exchanged between them. The principal axis of channel between two basins is located nearly in the north-south direction, thus it is natural that the water flow between the estuary and bay is influenced more by the north-south component of wind than the east-west component of that. Although the relationship between water exchange and the east-west component of wind is relatively low compared with the north-south component, the water exchange is controlled by this. In this study, using the field data measured by ADCP and CTD in summer months of 2009, a mechanism of wind-induced water exchange was investigated and discussed. A simple theoretical approach suggested that the dynamic response of density surface in Hamanako Bay to the wind force caused the circulating flow in the channel. The change of water density was more remarkable in Hamanako Bay than in Inohanako Estuary in response to the wind direction, and the surface layer in Hamanako Bay became thinner during the westerly wind. This study shows that the water exchange associated with the east-west wind is caused by the difference of water pressures between Inoahnako Estuary and Hamanako Bay, which is induced by the fluctuation of density interface between the surface and bottom layers due to wind.

Recent record-breaking high ocean waves induced by typhoons in the seas adjacent to Korea

ABSTRACT Moon, I.-J., Kim, M.; Joh, M., Ahn, J., Shim, J.-S., and Jung, J., 2016. Recent record-breaking high ocean waves induced by typhoons in the seas adjacent to Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1397 - 1401. Coconut Creek (Florida), ISSN 0749-0208. Estimation of extreme wave heights (EWHs) is the most important factor in the design of coastal structures such as breakwaters. In Korean coasts, the most EWHs occur during typhoon events. Recently, a number of ocean wave buoys have been deployed in the seas adjacent to Korea. This enables the measurement of record-breaking high waves during passages of recent strong Typhoons Kompasu (1007), Muifa (1109), Bolaven (1215), and Sanba (1216). This study investigates the characteristics of extreme waves during the passages of typhoons using buoy measurements and a numerical model. The wave simulations using WAVEWATCH III show that the model has the capability to reproduce the most EWHs during the four aforementioned typhoons with high accuracy, which guarantees an explanation of the mechanisms on the causes of such high wave generations over these regions. The analysis reveals that the occurrence of EWHs is influenced by not only storm intensity (i.e., maximum wind speed), but also the size, translation speed, and track of typhoons. Particularly, the record-breaking maximum wave height of 19.7 m observed during Typhoon Bolaven was the combined result of high winds, fast translation speed, big size, and straight track of Bolaven, which can maximize the increase of the dynamic fetch and duration.