Comparison of Turbulent Flows and Suspended Sediment Particle Motions Simulated around a Submerged Breakwater Using RANS and LES     

Yeon S. Chang  Jong Dae Do  Weon Mu Jeong  Sang Kwon Hyun  Won-Dae Baek  Jae Ho Choi  Jae-Youll Jin 《Ocean Science Journal》2020,55(1):1-16

Beach erosion is a serious problem that can be aggravated by human-made structures, and the modeling of breaking waves near the coast and around coastal st  相似文献   

Seismic stratigraphy of the western South Korea Plateau,East Sea: implications for tectonic history and sequence development during back-arc evolution     

Y. K. Kwon  S. H. Yoon  S. K. Chough 《Geo-Marine Letters》2009,29(3):181-189

The western South Korea Plateau in the East Sea (Sea of Japan) is occupied by rifted continental fragments formed in association with the early phase of back-arc opening. The present study focuses on the seismic stratigraphy of the sedimentary succession and the underlying acoustic basement in this region, based on closely spaced multichannel seismic reflection profiles. The sedimentary succession occurs mainly within a series of subparallel basement troughs (grabens or half grabens) bounded by faulted continental blocks (horsts) or volcanic ridges, and commonly floored by extrusive volcanic rocks showing hyperbolic reflectors. These features are strongly suggestive of continental rifting accompanied by normal faulting, volcanic activity and high rates of basin subsidence. The sedimentary succession can be subdivided into four seismic units. Unit 1 is characterized by short and irregular high-amplitude reflectors and interpreted as a syn-rift deposit consisting of a non-marine volcanics/sediment complex in topographic lows. Units 2 and 3 formed in an open marine environment during the Middle Miocene to Early Pliocene, characterized by an onlap-fill and later draping marine sedimentary succession dominantly composed of hemipelagic sediments and turbidites with frequent intercalation of mass-flow deposits. Along the western margin of the plateau, these units were deformed under a compressional regime in the Early Pliocene, associated with the back-arc closing phase. Unit 4 (deposited since the Early Pliocene) comprises hemipelagic sediments and turbidites with evidence of sporadic slides/slumps.  相似文献   

Stochastically-driven multidecadal variability of the Atlantic meridional overturning circulation in CCSM3   总被引：1，自引：1，他引：0  

Young-Oh Kwon  Claude Frankignoul 《Climate Dynamics》2012,38(5-6):859-876

The Atlantic meridional overturning circulation (AMOC) in the last 250?years of the 700-year-long present-day control integration of the Community Climate System Model version 3 with T85 atmospheric resolution exhibits a red noise-like irregular multi-decadal variability with a persistence longer than 10?years, which markedly contrasts with the preceding ~300 years of very regular and stronger AMOC variability with ~20?year periodicity. The red noise-like multi-decadal AMOC variability is primarily forced by the surface fluxes associated with stochastic changes in the North Atlantic Oscillation (NAO) that intensify and shift northward the deep convection in the Labrador Sea. However, the persistence of the AMOC and the associated oceanic anomalies that are directly forced by the NAO forcing does not exceed about 5?years. The additional persistence originates from anomalous horizontal advection and vertical mixing, which generate density anomalies on the continental shelf along the eastern boundary of the subpolar gyre. These anomalies are subsequently advected by the mean boundary current into the northern part of the Labrador Sea convection region, reinforcing the density changes directly forced by the NAO. As no evidence was found of a clear two-way coupling with the atmosphere, the multi-decadal AMOC variability in the last 250?years of the integration is an ocean-only response to stochastic NAO forcing with a delayed positive feedback caused by the changes in the horizontal ocean circulation.  相似文献   

On the role of Mn(IV) vacancies in the photoreductive dissolution of hexagonal birnessite   总被引：4，自引：0，他引：4  

Kideok D. Kwon  Keith Refson 《Geochimica et cosmochimica acta》2009,73(14):4142-1527

Photoreductive dissolution of layer type Mn(IV) oxides (birnessite) under sunlight illumination to form soluble Mn(II) has been observed in both field and laboratory settings, leading to a consensus that this process is a key driver of the biogeochemical cycling of Mn in the euphotic zones of marine and freshwater ecosystems. However, the underlying mechanisms for the process remain unknown, although they have been linked to the semiconducting characteristics of hexagonal birnessite, the ubiquitous Mn(IV) oxide produced mainly by bacterial oxidation of soluble Mn(II). One of the universal properties of this biogenic mineral is the presence of Mn(IV) vacancies, long-identified as strong adsorption sites for metal cations. In this paper, the possible role of Mn vacancies in photoreductive dissolution is investigated theoretically using quantum mechanical calculations based on spin-polarized density functional theory (DFT). Our DFT study demonstrates unequivocally that Mn vacancies significantly reduce the band-gap energy for hexagonal birnessite relative to a hypothetical vacancy-free MnO₂ and thus would increase the concentration of photo-induced electrons available for Mn(IV) reduction upon illumination of the mineral by sunlight. Calculations of the charge distribution in the presence of vacancies, although not fully conclusive, show a clear separation of photo-induced electrons and holes, implying a slow recombination of these charge-carriers that facilitates the two-electron reduction of Mn(IV) to Mn(II).  相似文献   

Simulation of atmospheric states for a storm surge on the west coast of Korea: model comparison between MM5, WRF and COAMPS     

Ki-Young Heo  Jeong-Wook Lee  Kyung-Ja Ha  Ki-Cheon Jun  Kwang-Soon Park  Jae-Il Kwon 《Natural Hazards》2009,51(1):151-162

High-quality informations on sea level pressure and sea surface wind stress are required to accurately predict storm surges over the Korean Peninsula. The storm surge on 31 March 2007 at Yeonggwang, on the western coast, was an abrupt response to mesocyclone development. In the present study, we attempted to obtain reliable surface winds and sea level pressures. Using an optimal physical parameterization for wind conditions, MM5, WRF and COAMPS were used to simulate the atmospheric states that accompanied the storm surge. The use of MM5, WRF and COAMPS simulations indicated the development of high winds in the strong pressure gradient due to an anticyclone and a mesocyclone in the southern part of the western coast. The response to this situation to the storm surge was sensitive. A low-level warm advection was examined as a possible causal mechanism for the development of a mesocyclone in the generating storm surge. The low-level warm temperature advection was simulated using the three models, but MM5 and WRF tended to underestimate the warm tongue and overestimate the wind speed. The WRF simulation was closer to the observed data than the other simulations in terms of wind speed and the intensity of the mesocyclone. It can be concluded that the magnitude of the storm surge at Yeonggwang was dependent, not only on the development of a mesocyclone but on ocean effects as well.  相似文献   

Decadal change in relationship between western North Pacific tropical cyclone frequency and the tropical Pacific SST   总被引：1，自引：0，他引：1  

Sang-Wook Yeh  Sok-Kuh Kang  Ben P. Kirtman  Joo-Hong Kim  Min-Ho Kwon  Cheol-Ho Kim 《Meteorology and Atmospheric Physics》2010,106(3-4):179-189

In this study, we examine the relationship between the number of tropical cyclones (TCs) in the western North Pacific and the tropical Pacific sea surface temperature (SST) during the main TC season (July–November) for the period of 1965–2006. Results show that there are periods when TC frequency and the tropical Pacific SST are well correlated and periods when the relationship breaks down. Therefore, decadal variation is readily apparent in the relationship between the TC frequency and the SST variations in the tropical Pacific. We further examine the oceanic and atmospheric states in the two periods (i.e., 1979–1989 vs. 1990–2000) when the marked contrast in the correlation between the TC frequency and the tropical Pacific SST is observed. Before 1990, the analysis indicates that oceanic conditions largely influenced anomalous TC frequency, whereas atmospheric conditions had little impact. After 1990, there the reverse appears to be the case, i.e., atmospheric conditions drive anomalous TC frequency and oceanic conditions are relatively unimportant. A role of atmosphere and ocean in relation to the TC development in the western North Pacific changes, which is consistent with the change of the correlations between the TC frequency and the tropical Pacific SST.  相似文献   

Structure change of Typhoon Nari (2007) in the weakening stage     

In-Hyuk Kwon  Hyeong-Bin Cheong  Hyun-Gyu Kang  Hyun-Jun Han  Ja-Rin Park 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(3):327-340

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Restoration of an inner-city stream and its impact on air temperature and humidity based on long-term monitoring data     

Kyu Rang KIM  Tae Heon KWON  Yeon-Hee KIM  Hae-Jung KOO  Byoung-Cheol CHOI  Chee-Young CHOI 《大气科学进展》2009,26(2):283-292

Spatiotemporal changes in air temperature and humidity associated with the restoration of an inner-city stream in Seoul, Korea, are investigated based on long-term monitoring data. The Cheonggye stream, covered under a concrete structure for 46 years, was restored in 2005 and runs 5.8 km eastward through a central region of Seoul. Long-term monitoring of the air temperature and relative humidity was made along the stream throughout the restoration and across the stream after the restoration. The area along the stream had a higher air temperature than the entire metropolitan area. The temperature anomaly between the monitoring area and the surrounding metropolitan area was 0.13^oC lower on average at the center of the stream after the restoration. The stream's effect on the air temperature was also evident in the temperature distribution along a street traversing the stream. The relative and specific humidities were increased due to the restoration. The restored stream modified the nearby urban climate in the opposite direction compared to urbanization. The results could be used as a model case in mitigating urban climate by a stream in future urban planning practices.  相似文献   

Error assessment of climate variables for FAO-56 reference evapotranspiration     

Hyojung Kwon  Minha Choi 《Meteorology and Atmospheric Physics》2011,112(1-2):81-90

Meteorological stations, which measure all the required meteorological parameters to estimate reference evapotranspiration (ET_o) using the Food and Agriculture Organization Penman?CMonteith (FAO56-PM) method, are limited in Korea. In this study, alternative methods were applied to estimate these parameters, and the applicability of these methods for ET_o estimation was evaluated by comparison with a complete meteorological dataset collected in 2008 in Korea. Despite differences between the estimation and observation of radiation and wind speed, the comparison of ET_o showed small differences [i.e., mean bias error (MBE) varying ?0.22 to 0.25?mm?day^?1 and root-mean-square-error (RMSE) varying 0.06?C0.50?mm?day^?1]. The estimated vapor pressure differed considerably from the observed, resulting in a larger discrepancy in ET_o (i.e., MBE of ?0.50?mm?day^?1 and RMSE of 0.60?C0.73?mm?day^?1). Estimated ET_o showed different sensitivity to variations of the meteorological parameters??in order of vapor pressure?>?wind speed?>?radiation. It is clear that the FAO56-PM method is applicable for reasonable ET_o estimation at a daily time scale especially in data-limited regions in Korea.  相似文献   

An operational MODIS aerosol retrieval algorithm at high spatial resolution,and its application over a complex urban region     

Man Sing Wong  Janet E. Nichol  Kwon Ho Lee 《Atmospheric Research》2011,99(3-4):579-589

Aerosol retrieval algorithms for the MODerate Resolution Imaging Spectroradiometer (MODIS) have been developed to estimate aerosol and microphysical properties of the atmosphere, which help to address aerosol climatic issues at global scale. However, higher spatial resolution aerosol products for urban areas have not been well-researched mainly due to the difficulty of differentiating aerosols from bright surfaces in urban areas. Here, an aerosol retrieval algorithm using the MODIS 500-m resolution bands is described, to retrieve aerosol properties over Hong Kong and the Pearl River Delta region. The rationale of our technique is to first estimate the aerosol reflectances by decomposing the top-of-atmosphere reflectances from surface reflectances and Rayleigh path reflectances. For the determination of surface reflectances, a Minimum Reflectance Technique (MRT) is used, and MRT images are computed for different seasons. For conversion of aerosol reflectance to aerosol optical thickness (AOT), comprehensive Look Up Tables specific to the local region are constructed, which consider aerosol properties and sun-viewing geometry in the radiative transfer calculations. Four local aerosol types, namely coastal urban, polluted urban, dust, and heavy pollution, were derived using cluster analysis on 3 years of AERONET measurements in Hong Kong. The resulting 500 m AOT images were found to be highly correlated with ground measurements from the AERONET (r² = 0.767) and Microtops II sunphotometers (r² = 0.760) in Hong Kong. This study further demonstrates the application of the fine resolution AOT images for monitoring inter-urban and intra-urban aerosol distributions and the influence of trans-boundary flows. These applications include characterization of spatial patterns of AOT within the city, and detection of regional biomass burning sources.  相似文献