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131.
Hyein Park Chul E. Chung Annica M. L. Ekman Jung-Ok Choi 《Asia-Pacific Journal of Atmospheric Sciences》2014,50(3):377-390
This study examines and evaluates simulated aerosol optical depth (AOD) and fine-mode AOD (fAOD) from the ACCMIP and CMIP5 global model archives. Satellite data nudged to AERONET data are used to construct reliable global observations of AOD and fAOD for validating the simulations. The difference in simulated global average AOD among models is of the order of a factor of 2, and the difference is even larger (~factor of 3) for fAOD. Compared to the observations, the models tend to underestimate AOD and fAOD significantly over eastern China. Another important discrepancy is that the models show larger fAOD over the Indus-Ganga Plain in summer than in winter, whereas the observations display an opposite feature. The models also overestimate the fAOD over the biomass burning regions of central Africa in DJF and underestimate the fAOD over the biomass burning regions of southern Africa in JJA. To evaluate the effect of the discrepancy between modeled and observed fAOD on aerosol direct radiative forcing, an offline radiation model is utilized. Comparing the model-fAODderived fine-mode forcing with the fine-mode forcing derived from the fAOD observation, the models tend to give too large (negative) value. This result implies that the calculated anthropogenic aerosol forcing in ACCMIP and CMIP5 models has a negative bias. 相似文献
132.
Choon-Ki?Lee Shin-Chan?HanEmail author Dieter?Bilitza Jong-Kyun?Chung 《Journal of Geodesy》2011,85(12):921-929
The in situ measurements of electron contents from GRACE K-band (dual-frequency) ranging system and CHAMP planar Langmuir
probe were used to validate the international reference ionosphere (IRI) models. The comparison using measurements from year
2003 to 2007 shows a general agreement between data and the model outputs. The improvement in the newer IRI model (IRI-2007)
is evident with the measurements from the GRACE satellites orbiting at the higher altitude. We present the comparison between
the models and data comprehensively for various cases in solar activity, local time, season, and latitude. The IRI models
do not well predict the electron density in the years 2006 and later, when the solar activity is extremely low. The IRI models
generally overestimate the electron density during local winter while they underestimate during local summer. In the equatorial
region, the large difference at local sunrise lasts for all years and all seasons. The IRI models do not perform well in predicting
the anomaly in the polar region such as the Weddell Sea Anomaly. These discrepancies are likely due to smoothed (12-month
averaged) solar activity indices used in the IRI models and due to insufficient spherical harmonic representation not able
to capture small spatial scales. In near future, further improvement on the IRI models is expected by assimilating those in
situ satellite data by implementing higher resolution (spatial and temporal) parameterizations. 相似文献
133.
Di-Cheng Zhu Zhi-Dan Zhao Yaoling Niu Xuan-Xue Mo Sun-Lin Chung Zeng-Qian Hou Li-Quan Wang Fu-Yuan Wu 《Earth and Planetary Science Letters》2011,301(1-2):241-255
The Lhasa Terrane in southern Tibet has long been accepted as the last geological block accreted to Eurasia before its collision with the northward drifting Indian continent in the Cenozoic, but its lithospheric architecture, drift and growth histories and the nature of its northern suture with Eurasia via the Qiangtang Terrane remain enigmatic. Using zircon in situ U–Pb and Lu–Hf isotopic and bulk-rock geochemical data of Mesozoic–Early Tertiary magmatic rocks sampled along four north–south traverses across the Lhasa Terrane, we show that the Lhasa Terrane has ancient basement rocks of Proterozoic and Archean ages (up to 2870 Ma) in its centre with younger and juvenile crust (Phanerozoic) accreted towards its both northern and southern edges. This finding proves that the central Lhasa subterrane was once a microcontinent. This continent has survived from its long journey across the Paleo-Tethyan Ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the Qiangtang Terrane to the north and with the Indian continent to the south. Zircon Hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks (e.g., ~ 50–90%, 0–70%, and 30–100% to the Mesozoic magmatism in the southern, central, and northern Lhasa subterranes, respectively). We suggest that much of the Mesozoic magmatism in the Lhasa Terrane may be associated with the southward Bangong–Nujiang Tethyan seafloor subduction beneath the Lhasa Terrane, which likely began in the Middle Permian (or earlier) and ceased in the late Early Cretaceous, and that the significant changes of zircon εHf(t) at ~ 113 and ~ 52 Ma record tectonomagmatic activities as a result of slab break-off and related mantle melting events following the Qiangtang–Lhasa amalgamation and India–Lhasa amalgamation, respectively. These results manifest the efficacy of zircons as a chronometer (U–Pb dating) and a geochemical tracer (Hf isotopes) in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics. 相似文献
134.
An open problem that arises when using modern iterative linear solvers, such as the preconditioned conjugate gradient method or Generalized Minimum RESidual (GMRES) method, is how to choose the residual tolerance in the linear solver to be consistent with the tolerance on the solution error. This problem is especially acute for integrated groundwater models, which are implicitly coupled to another model, such as surface water models, and resolve both multiple scales of flow and temporal interaction terms, giving rise to linear systems with variable scaling. This article uses the theory of "forward error bound estimation" to explain the correspondence between the residual error in the preconditioned linear system and the solution error. Using examples of linear systems from models developed by the US Geological Survey and the California State Department of Water Resources, we observe that this error bound guides the choice of a practical measure for controlling the error in linear systems. We implemented a preconditioned GMRES algorithm and benchmarked it against the Successive Over-Relaxation (SOR) method, the most widely known iterative solver for nonsymmetric coefficient matrices. With forward error control, GMRES can easily replace the SOR method in legacy groundwater modeling packages, resulting in the overall simulation speedups as large as 7.74×. This research is expected to broadly impact groundwater modelers through the demonstration of a practical and general approach for setting the residual tolerance in line with the solution error tolerance and presentation of GMRES performance benchmarking results. 相似文献
135.
Characterizing lipid biomarkers in methanotrophic communities of gas hydrate-bearing sediments in the Sea of Okhotsk 总被引:1,自引:0,他引:1
Jin-Yong Yang Kyung-Ho Chung Young-Keun Jin Kyung-Hoon Shin 《Marine and Petroleum Geology》2011,28(10):1884-1898
We studied specific lipid biomarkers of archaea and bacteria, that are associated with the anaerobic oxidation of methane (AOM) in a cold seep environment as well as the origin of sedimentary organic matter on the continental slope off NE Sakhalin in the Sea of Okhotsk. The organic geochemical parameters demonstrated that most of the sedimentary organic matter containing hydrate layers could be derived from marine phytoplankton and bacteria, except for a station (LV39-29H) which was remarkably affected by terrestrial vascular plant. Specific methanotrophic archaea biomarkers was vertically detected in hydrate-bearing cores (LV39-40H), coinciding with the negative excursion of the δ13Corg at core depths of 90–100 cm below the seafloor. These results suggest that methane provided from gas hydrates are already available substrates for microbes thriving in this sediment depth. In addition, the stable isotope mass balance method revealed that approximately 2.77–3.41% of the total organic carbon (or 0.036–0.044% dry weight sediment) was generated by the activity of the AOM consortium in the corresponding depth of core LV39-40H. On the other hand, the heavier δ13C values of archaeol in the gas hydrate stability zone may allow ongoing methanogenesis in deeper sediment depth. 相似文献
136.
Fengqing Li Namil Chung Mi-Jung Bae Yong-Su Kwon Tae-Sung Kwon Young-Seuk Park 《Climatic change》2013,119(2):421-434
Peninsular environments are ecosystems that are one of the most vulnerable to global warming. Despite the importance of conserving regional biodiversity, peninsular environments are among the least studied with respect to the influences of global warming. In this study, we used data on benthic macroinvertebrate communities from 521 sites across Korea (a nationwide scale) to evaluate the potential impact of temperature increases on river ecosystems. Weighted averaging regression models (WARMs) were used to project the relationships between relative macroinvertebrate abundance and water temperature, based on the temperature data of the Intergovernmental Panel on Climate Change (IPCC) A1B scenario. Maximum tolerance water temperatures were used to quantify the risks to macroinvertebrates at the catchment and national scales. Ambient air temperatures in the 2090s were projected to increase by an average of 3.4?ºC relative to the baseline of the 2000s at the national scale. Mayflies, stoneflies and caddisflies were identified as potentially the most sensitive taxa to global warming. The impact of global warming on macroinvertebrates was predicted to be minimal prior to the 2060s; however, by the 2080s, species loss was predicted to be 55 %. Potential distribution ranges of cold water species in the future decades were expected to decrease continuously over time, while those of warm species were expected to increase from the 2000s to the 2040s and then decrease until the 2080s. Our projections may be useful for understanding how climate parameters affect the biogeographical patterns of aquatic biodiversity from a thermal-preference perspective. 相似文献
137.
Grid adaptive methods combined with domain adaptation are discussed for two-dimensional seepage flow problems with free boundaries through porous media. Examples of grid and domain adaptive methods are presented to demonstrate several ways to predict grids and shapes of free boundaries using an iterative scheme. Finally, the combined adaptive methods are applied to obtain smooth non-oscillatory shape of a free boundary of seepage flow through non-homogeneous porous media. 相似文献
138.
Journal of Oceanology and Limnology - Hong Kong has a long historical record of harmful algal blooms (HABs). In the 1980s–1990s, HABs were mainly pollution-related and most of the events... 相似文献
139.
A. Nguyen Van Nghia Jougnot Damien Thanh Luong Duy Van Do Phan Thuy Tran Thi Chung Hue Dang Thi Minh Hung Nguyen Manh 《Hydrogeology Journal》2021,29(6):2017-2031
Hydrogeology Journal - Predicting the permeability of porous media in saturated and partially saturated conditions is of crucial importance in many geo-engineering areas, from water resources to... 相似文献
140.
S. Selvam C. Singaraja S. Venkatramanan S. Y. Chung 《Journal of the Geological Society of India》2018,92(3):313-320
Groundwater qualities of coastal aquifers in the Ottapidaram taluk of Thoothukudi district, Tamil Nadu have been extensively monitored in post monsoon seasons in 2014 to assess its suitability in relation to domestic and drinking uses in four regions (N-S-EW). 34 groundwater samples were analyzed for various physicochemical attributes like pH, electrical conductivity (EC), Total dissolved solid (TDS), Na, K, Ca, Mg, Cl, HCO3, CO3, SO4, NO3, PO4. Most of these parameters fall under not permissible limits. The western part of the study area is highly polluted from K, Cl, HCO3 due to industrial/agriculture activity. The southern part is less polluted compared to other region. Hydrogeochemical processes controlling the water chemistry (Gibbs) indicates that most of groundwater samples fall at rock-weathering supremacy zone. Geochemical processes and temporal variation in the groundwater in this area are influenced by evaporation processes, ion exchange and dissolution of minerals. Major cation and anion ionic interaction indicate that weathering reactions have an inconsequential role in the hydrochemical processes of the shallow groundwater system. As a result of the hydrogeochemical analysis, seawater intrusion, aquifer rock weathering, sewer leakage are the overriding factors that determine the major ionic composition. The appropriate management plan is necessary to preserve precious groundwater resources. 相似文献