Cheol-Ho Kim

Wavelet Galerkin METHODES FOR GAME THEORETIC CONTROL OF DISTRIBUTED PARAMETER SYSTEMS

This paper presents a novel strategy for obtaining finite dimensional approximations of Riccati operators arising in game theoretic control problems on Hilbert spaces. While extensive progress has been made in the utilization of the newly developed field of wavelet analysis in signal and image processing, for less progress has been made in applicationa to computational mechanics. This fact is surprising considering the inherent multiresolution properties of wavelet analysis. This paper derives a wavelet galerkin formulation of a specific class of computational control problems: zero sum dynamic games on Hilbert spaces. This work extends previous research in that not only are convergence, exponential stability and robust stability of soft constrained differtial games on Hilbert spaces considered, but quantitative numerical conditioning results are also presented. In fact, a precise bound is given on the error induced by truncating wavelet quadratures used in the weak formulation of computational control problems. The theory presented is verified by modeling a robust control strategy for a beam subjected to piezocerarnic actuation and structured uncertainty.

Long-term Variability of Sea Surface Temperature in the East China Sea: A Review

The long-term variability of sea surface temperature in the East China Sea was reviewed based mainly on published literatures. Though the quantitative results are not the same, it is generally shown that sea surface temperature is increasing especially in recent years with the rate of increase about 0.03℃/year. Other meaningful results presented in the literatures is that the difference of water properties between layers upper and lower than the thermocline in summer shows an increasing trend both in temperature and salinity, suggesting that the stratification has been intensified. As a mechanism by which to evaluate the wintertime warming trend in the region, the weakening of wind strength, which is related to the variation of sea level pressure and atmospheric circulation in the western North Pacific and northern Asian continent, is suggested in the most of related studies.

Seasonal variation of semidiurnal internal tides in the East/Japan Sea

The seasonal variation of semidiurnal internal tides in the East/Japan Sea was investigated using 25 month long output from a real-time ocean forecasting system. The z coordinate eddy-resolving high-resolution numerical model, called the RIAM ocean model, incorporates data assimilation that nudges temperature and salinity fields together with volume transport through the Korea Strait to produce realistic oceanic currents and stratification. In addition to atmospheric forcing, it includes tidal forcing of 16 major components along open boundaries. The model generates energetic semidiurnal internal tides around the northern entrance of the Korea Strait. Energy conversion from barotropic to baroclinic (internal) tides varies seasonally with maxima in September (ranging 0.48–0.52 GW) and minima in March (ranging 0.11–0.16 GW). This seasonal variation is induced by the seasonality in stratification near the southwestern East/Japan Sea. The propagation distance of the internal tides is associated with generation intensity and wavelength. From late summer to early winter, the semidiurnal internal tides travel relatively far from the generation region due to stratification changes; its energy dissipates less as a result of longer wavelengths. Our results suggest that spatiotemporal variation of internal-tide-induced mixing due to the seasonality in the generation, propagation, and dissipation of internal tides should be considered for a more realistic simulation of water masses and circulation in models of the East/Japan Sea.

지구시스템모형을 이용한 황동중국해 이산화탄소분압 분포 특성 평가

Using results from an earth system model, the distribution of partial pressure of CO₂ (pCO₂) in surface seawater over the East China Sea is investigated. In this area pCO₂ shows minimum along the edge of the continental break along the path of the Taiwan-Tsushima Current System. Apparently modelled chlorophyll is also great along the current but the maximum of the chlorophyll and the minimum of pCO₂ do not coincide suggesting that the primary production is not the main cause of the pCO₂ minimum. As we move toward the Yellow Sea from the Kuroshio area the temperature decreases so that the pCO₂ becomes smaller. If we move further toward the Yellow Sea beyond the Taiwan-Tsushima Current System, alkalinity starts to drop substantially to intensify pCO₂ while overcoming the effect of decreasing temperature and salinity. Thus pCO₂ minimum occurs along the Taiwan-Tsushima Current System. Of course, the primary production lower pCO₂ during spring when it is high but the effect is local. Near the Yangtze river mouth and northeastern corner of the Yellow Sea the fresh water input is large enough and dissolved inorganic carbon (DIC) becomes low enough so that pCO₂ becomes lower again.

Correction to “Patterns of recent sea level rise in the East/Japan Sea from satellite altimetry and in situ data”

[1] In the paper ‘‘Patterns of recent sea level rise in the East/Japan Sea from satellite altimetry and in situ data’’ by Sok Kuh Kang et al. (Journal of Geophysical Research, 110, C07002, doi:10.1029/2004JC002565, 2005), the boxes around regions UB,YB, YR, and SE were inadvertently dropped from Figure 1. The correct figure and its caption appear below. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, C07006, doi:10.1029/2005JC003413, 2006

Analysis of Sea Surface Temperature Simulation in the Northwestern Pacific and the East Asian Marginal Seas using HadGEM2-AO

In this study, we evaluated the model performance with respect to Sea Surface Temperature (SST) and Net Heat Flux (NHF) by considering the characteristics of seasonal temperature variation and contributing factors and by analyzing heat budget terms in the Northwestern Pacific and East Asian Marginal Seas (110˚E−160˚E, 15˚N−60˚N) using the HadGEM2-AO historical run. Annual mean SST of the HadGEM2-AO is about 0.065oC higher than observations (EN3_v2a) from 1950 to 2000. Since 1960, the model has simulated well the long-term variation of SST and the increasing rate of SST in the model (0.014℃/year) is comparable with observations (0.013℃/year). Heat loss from the ocean to the atmosphere was simulated slightly higher in the HadGEM2-AO than that in the reanalysis data on the East Asian Marginal Seas and the Kuroshio region. We investigated the causes of temperature variation by calculating the heat budget equation in the two representative regions. In the central part of the Kuroshio axis (125˚E−130˚E, 25˚N−30˚N: Region A), both heat loss in the upper mixed layer by surface heat flux and vertical heat advection mainly cause the decrease of heat storage in autumn and winter. Release of latent heat flux through the heat convergence brought about by the Kuroshio contributes to the large surface net heat flux. Positive heat storage rate is mainly determined by horizontal heat advection from March to April and surface net heat flux from May to July. In the central part of the subtropical gyre (155˚E−160˚E, 22˚N−27˚N: Region B), unlike Region A, vertical heat advection predominantly causes the decrease of heat storage in autumn and winter. In spring and summer, surface heat flux contributes to the increase of heat storage in Region B and the period is two times longer than the period for Region A. In this season, shoaling of the mixed layer depth plays an important role in the increase of SST.