Ki-Young Heo

Interdecadal changes in the storm track activity over the North Pacific and North Atlantic

Analysis of NCEP-NCAR I reanalysis data of 1948–2009 and ECMWF ERA-40 reanalysis data of 1958–2001 reveals several significant interdecadal changes in the storm track activity and mean flow-transient eddy interaction in the extratropics of Northern Hemisphere. First, the most remarkable transition in the North Pacific storm track (PST) and the North Atlantic storm track (AST) activities during the boreal cold season (from November to March) occurred around early-to-mid 1970s with the characteristics of global intensification that has been noticed in previous studies. Second, the PST activity in midwinter underwent decadal change from a weak regime in the early 1980s to a strong regime in the late 1980s. Third, during recent decade, the PST intensity has been enhanced in early spring whereas the AST intensity has been weakened in midwinter. Finally, interdecadal change has been also noted in the relationship between the PST and AST activities and between the storm track activity and climate indices. The variability of storm track activity is well correlated with the Pacific Decadal Oscillation and North Atlantic Oscillation prior to the early 1980s, but this relationship has disappeared afterward and a significant linkage between the PST and AST activity has also been decoupled. For a better understanding of the mid-1970s’ shift in storm track activity and mean flow-transient eddy interaction, further investigation is made by analyzing local barotropic and baroclinic energetics. The intensification of global storm track activity after the mid-1970s is mainly associated with the enhancement of mean meridional temperature gradient resulting in favorable condition for baroclinic eddy growth. Consistent with the change in storm track activity, the baroclinic energy conversion is significantly increased in the North Pacific and North Atlantic. The intensification of the PST and AST activity, in turn, helps to reinforce the changes in the middle-to-upper tropospheric circulation but acts to interfere with the changes in the low-tropospheric temperature field.

A Coupled Model Study on the Formation and Dissipation of Sea Fogs

Abstract This study examined the impact of air–sea coupling using a coupled atmosphere–ocean modeling system consisting of the Coupled Ocean–Atmosphere Mesoscale Prediction System as the atmospheric component and the Regional Ocean Modeling System as the oceanic component. Numerical experiments for advection and steam fog events were carried out to clarify the modulation of the formation and dissipation of sea fogs by the air–sea temperature difference (air temperature minus sea surface temperature) and the atmospheric stability. The coupled simulation showed that advection fog is obviously controlled by low-level atmospheric stability and downward latent heat flux with oceanic cooling through air–sea coupling. In particular, air–sea coupling stabilizes the low-level atmosphere at the dissipation stage, and then suppresses vertical mixing, which retards the dissipation of advection fog. In the case of a steam fog event, the upward turbulent heat fluxes are increased significantly from the formation time t...

Changes in climate classification and extreme climate indices from a high-resolution future projection in Korea

We investigate the future changes in the climate zone and six extreme temperature indices in Korea, using the 20-km high-resolution atmospheric general circulation model (MRI-AGCM3.1S). The Trewartha and Köppen climate classification schemes are applied, and four summer-based extreme temperature indices (i.e., summer days, tropical nights, growing degree days, and cooling degree days (CDD) and two winter-based indices (frost days and heating degree days (HDD) are analyzed. To represent significantly the change in threshold indices, the monthly mean bias is corrected in model. The model result reasonably captures the temporal and spatial distribution of the present-day extreme temperatures associated with topography. It was found that in the future climate, the area of the subtropical climate zone in Korea expands northward and increases by 21% under the Trewartha classification scheme and by 35% under the Köppen classification scheme. The spatial change in extreme climate indices is significantly modulated by geographical characteristics in relation to land-ocean thermal inertia and topographical effects. The change is manifested more in coastal regions than in inland regions, except for that in summer days and HDD. Regions with higher indices in the present climate tend to reveal a larger increase in the future climate. The summer-based indices display an increasing trend, while the winter-based indices show a decreasing trend. The most significant increase is in tropical nights (+452%), whereas the most significant decrease is in HDD (−25%). As an important indicator of energy-saving applications, the changes in HDD and CDD are compared in terms of the frequency and intensity. The future changes in CDD reveal a higher frequency but a lower temperature than those in HDD. The more frequent changes in CDD may be due to a higher and less dispersed occurrence probability of extreme temperatures during the warm season. The greater increase in extreme temperature events during the summer season remains an important implication of projecting future changes in extreme climate events.

Development of the Operational Oceanographic System of Korea

The Korea Operational Oceanographic System (KOOS) was developed at the Korea Institute of Ocean Science and Technology (KIOST) to produce real-time forecasting and simulation of interdisciplinary multi-scale oceanic fields. This offers valuable information to better mitigate coastal disasters, such as oil spills and other marine accidents, and provides the necessary ocean predictions to support the marine activities of government agencies, marine industries, and public users. The KOOS became operational in March 2012, and consists of several operational modules and realtime observations, including satellite remote sensing, coastal remote monitoring stations using high-frequency radar, and ocean observatories. The basic forecasting system includes weather, regional and high-resolution coastal circulation and wave prediction models; the practical application system includes storm surges, oil spills, and search and rescue prediction models. An integrated maritime port prediction system and data information and skill assessment systems are also part of the KOOS. In this work, the performance of the numerical models was evaluated by the skill assessment systems. From the monthly and yearly skill assessments, the models showed reasonable skill in predicting atmospheric and oceanic states except for the regional ocean circulation models. The ongoing development and improvement of the KOOS includes improvement of the model skills through the upgrade of the satellite-based sea surface temperature algorithm, the enhancement of the ocean monitoring ability, the upgrade of the forecasting models for higher spatial resolutions and the application of data assimilation techniques improved with the feedback from the skill assessment report.

Antitumor Activity of TRAIL Recombinant Adenovirus in Human Malignant Glioma Cells

Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL) has been reported to specifically kill malignant cells but to be relatively nontoxic to normal cells. One of disadvantages to previous in vivo protocols was the need for large quantities of TRAIL recombinant protein to suppress tumor growth. To evaluate the antitumor activity and therapeutic value of the TRAIL gene, we constructed adenoviral vectors expressing the human TRAIL gene (Ad.hTRAIL) and transferred them into malignant glioma cells in vitro and tumors in vivo, as an alternative to recombinant soluble TRAIL protein. The results show that TRAIL-sensitive glioma cells infected Ad.hTRAIL undergo apoptosis through the production and expression of TRAIL protein. The in vitro transfer elicited apoptosis, as demonstrated by the quantification of viable or apoptotic cells and by the analysis of cleavage of poly (ADP-ribose) polymerase. Furthermore, in vivo administration of Ad.hTRAIL at the site of tumor implantation suppressed the outgrowth of human glioma xenografts in SCID mice. These results further define Ad.hTRAIL as an anti-tumor therapeutic and demonstrate its potential use as an alternative approach to treatment for malignant glioma.

Warming of Western North Pacific Ocean and Energetics of Transient Eddy Activity

AbstractThis study examines the increase in the sea surface temperature (SST) in the western North Pacific Ocean (WNPO) during December–February for the period 1959–2008. The relationship of this SST increase with significant interdecadal changes in the baroclinicity and the energetics of transient eddy activity is also examined. These results show that the interannual variations of the WNPO SST and atmospheric conditions including baroclinicity and turbulent heat flux are responses to the upstream atmospheric forcings associated with the East Asian winter monsoon (EAWM). For the interdecadal variations, the intensified baroclinicity downstream of the Pacific storm-track activity is responsible for an increase in the baroclinic energy conversion (BCEC) from the mean available potential energy (MAPE) to the eddy available potential energy (EAPE) to the east of 180°. This in turn increases the BCEC from the EAPE to the eddy kinetic energy (EKE) over this region. The BCEC and generation of EAPE by diabatic h...

Abnormal storm waves around the Korean Peninsula: A case study of an extratropical explosive cyclone over East Sea

ABSTRACT Heo, K.-Y., Shim, J.-S., Kwon, J.-I., Jeong, J.-Y., Park, K.-S. and Choi, J.-W., 2013. Abnormal storm waves around the Korean Peninsula: A case study of an extratropical explosive cyclone over East Sea. On April 3, 2012, an extratropical explosive cyclone developed over East Sea, producing heavy rainfall and strong winds. This cyclone produced maximum wind speeds of up to around 21 m s−1 over the ocean around Korea. As the explosive cyclone developed rapidly from 00 UTC April 3, 2012, it began to affect the coastal areas, and abnormal storm waves were generated by the strong wind. The observed maximum wave heights and periods around Korea were 11.1 m and 9.1 s at Chilbaldo, 12.0 m and 9.1 s at Marado, and 13.7 m, and 5.8 s at Ulleungdo in the period 04–10 UTC April 3, 2012. The objectives of this study are to investigate the mechanisms and conditions favorable for the development of the explosive cyclone, and to investigate the influence of the cyclone on the abnormal storm waves. To achieve the above objectives, numerical studies are conducted using the Weather Research and Forecasting (WRF) model as an atmospheric model and the open ocean wave model WAM. The explosive cyclone is amplified by latent heat release as well as the formation of an upper-level cut-off low, which resulted in the rapid intensification of the cyclone; while surface heat fluxes had a lesser contribution to the explosion of the cyclone. In situ meteorological observation data and wave data from buoy measurements for this event are available for comparison and validation. The comparisons show that the WRF and WAM models can accurately predict the wind speed and wave height.

Model Optimization for Sea Surface Wind Simulation of Strong Wind Cases

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.

Evaluation of Wind and Wave Simulations using Different Global Reanalyses

ABSTRACT Heo, K.-Y.; Ha, T.; Choi, J.-Y.; Park, K.-S.; Kwon, J.-I., and Jun, K., 2017. Evaluation of wind and wave simulations using different global reanalyses. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 99–103. Coconut Creek (Florida), ISSN 0749-0208. Sea surface wind plays an important role in oceanic phenomena and coastal environment. There are many sources of meteorological data available, both global and regional, and they differ not only in spatial and temporal resolution, but also in the number of observations included in the reanalysis and in the method of data assimilation used. The performance of the weather research and forecasting (WRF) model and its variational data assimilation system (WRFDA) with two global reanalyses (ERA-Interim and NCEP FNL) used as initial and lateral boundary conditions has been assessed during the period from January to December of 2014. Both WRF model simulations using the ERA-interim and the NCEP FNL are in good agreement with observations, with correlation coefficients for 10-m wind speed ranging from 0.81 to 0.88 and from 0.77 to 0.88, respectively. Both the ERA-Interim and the NCEP FNL are good choices for the models initial and lateral boundary conditions, while the ERA-Interim simulation showed better results for surface pressure, wind direction and speed. As a result, the ERA-Interim simulation shows better results for the significant wave height and mean wave period. The results of this study should provide some guidance for the improvement and development of WRF simulation, skill assessment of numerical weather prediction systems, and guidance for further research. Furthermore, the reanalyses can be useful for offshore and coastal researchers in estimating extreme sea states and designing specific offshore and coastal structures.