Effects of large-scale wind on the Kuroshio path south of Japan in a 60-year historical OGCM simulation     

Hiroyuki Tsujino  Shiro Nishikawa  Kei Sakamoto  Norihisa Usui  Hideyuki Nakano  Goro Yamanaka 《Climate Dynamics》2013,41(9-10):2287-2318

The effects of large-scale wind forcing on the bimodality of the Kuroshio path south of Japan, the large meander (LM) and non-large meander (NLM), were studied by using a historical simulation (1948–2007) with a high-resolution Ocean general circulation models (OGCM). The Kuroshio in this simulation spent much time in the NLM state, and reproduced several aspects of its long-term path variability for the first time in historical OGCM simulation, presumably because the eddy kinetic energy was kept at a moderate level. By using the simulated fields, the relationships between wind forcing (or Kuroshio transport) and path variation proposed by past studies were tested, and specific roles of eddies in those variations were investigated. The long-term variation of the simulated net Kuroshio transport south of Japan was largely explained by the linear baroclinic Rossby wave adjustment to wind forcing. In the simulated LM events, a triggering meander originated from the interaction of a wind-induced positive sea surface height (SSH) anomaly with the upstream Kuroshio and was enlarged by cyclonic eddies from the recirculation gyre. The cyclonic eddy of the trigger meander was followed by a sizable anticyclonic eddy on the upstream side. Subsequently, a weak (strong) Kuroshio favored the LM (NLM). The LM tended to be maintained when the Kuroshio transport off southern Japan was small, and increasing Kuroshio transport promoted decay of an existing LM. The supply of disturbances from upstream, which is related to the wind-induced SSH variability at low latitudes, contributed to the maintenance of an existing LM.  相似文献   

The dependence of surface tidal stress on the internal structure of Europa: The possibility of cracking of the icy shell     

Yuji Harada  Kei Kurita 《Planetary and Space Science》2006,54(2):170-180

This study shows dependence of the surface diurnal tidal stress on the internal structure of Europa. Its purpose is to investigate possibility of cracking of the icy shell. The stress is evaluated under the plausible model of the internal structure constrained by the gravity field data. The possible effective stress at the sub-Jovian point decreases with thickening of the shell, while it does not depend on the core radius and the thickness of the H₂O layer. The range of this value is from 0.095 to 0.161 MPa, which does not exceed the tensile strength of ice. The stress required for the surface cracking would be mainly due to longer period deformations, especially non-synchronous rotation. And/or the actual strength of the ice at the surface would be smaller because of the preexisting cracks than that at a laboratory of the same temperature.  相似文献   

Statistical analyses and modeling approaches to hydrodynamic characteristics in alluvial aquifer     

Chie Imagawa  Junichiro Takeuchi  Toshihiko Kawachi  Shunsuke Chono  Kei Ishida 《水文研究》2013,27(26):4017-4027

This study is aimed at quantifying the difference in aquifer's response to recharge between some different locations in a fan aquifer and a delta aquifer for a preliminary study of revealing mechanisms of water transport in alluvial aquifer. The aquifer's response to recharge is statistically quantified with the two viewpoints: (1) timing and volume of recharge and (2) time length of aquifer's holding water. For the first point, a statistical model that links precipitation and groundwater level is introduced, and its parameters are identified using correlation analysis. Our results show that the recharge rate at the toe is higher than that at the apex and at the delta. For the second point, the concept of ‘memory effect’ of aquifer is adopted and quantified using the autocorrelation and spectral analyses. Our results show that the memory effect is longer at the toe of fan than at the apex, and thus, a temporary increase of water level has about five times as long‐term influence on subsequent water levels at the toe of the fan as at the apex. This study demonstrates that the statistical analyses and modeling of hydrological data are useful for characterizing aquifer's hydrodynamics. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Field measurement and modeling of near-bed sediment transport processes with fluid mud layer in Tokyo Bay     

Nakagawa  Yasuyuki  Nadaoka  Kazuo  Yagi  Hiroshi  Ariji  Ryuichi  Yoneyama  Haruo  Shirai  Kazuhiro 《Ocean Dynamics》2012,62(10):1535-1544

Tokyo Bay is one of the estuaries in Japan with a high population of almost 26 million people in the basin area. One of the major concerns for the environment in this water area is the decreasing ecosystem functions including the deterioration of water and sediment qualities caused by various anthropogenic activities. Since the bottom sediments around almost the entire area of the inner bay consist of fine materials with a high organic content, which cause the deterioration of water quality through processes such as hypoxia, an understanding of the fine sediment dynamics in the Bay is crucial for an environmental assessment of the water area. This paper proposes a model for the key processes of fine sediment dynamics, which reflects field data about muddy bed structures and their dynamics obtained during the monitoring campaign in 2007. One of the specific features of the sediment in the Bay at present is the persistent existence of fluid mud layers (water content over 300 %) with a thickness of around a few decimeters, which might be caused by deposition of abundant organic particles due to eutrophication. The present study shows that diffusion flux model delivers quite reliable results for estimating erosion flux from the top of fluid mud layers after calibrating the model parameter against the time series data of vertical flux measured by an acoustic Doppler velocimeter system. This study also derives analytical solutions, based on the Bingham fluid concept, of advection flux in the fluid mud layer on which external shear stress force is applied.

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Long-range transport of particulate polycyclic aromatic hydrocarbons at Cape Hedo remote island site in the East China Sea between 2005 and 2008     

Kei Sato  Hong Li  Yurie Tanaka  Shiho Ogawa  Yuka Iwasaki  Akinori Takami  Shiro Hatakeyama 《Journal of Atmospheric Chemistry》2008,61(3):243-257

Particle-associated polycyclic aromatic hydrocarbons (PAHs) in outflow from East Asia were observed at Cape Hedo, Okinawa, Japan between 2005 and 2008. The filter samples of the total suspended particles were analyzed by means of gas chromatography-mass spectrometry. The total concentration of fourteen 3–7-ring PAHs was 0.01–24 ng m^?3 (average 1.6 ng m^?3). The average PAH concentration increased in the winter-spring season and decreased in the summer-fall season. The average benzo(a)pyrene to benzo(e)pyrene ratio was 0.49 in the winter-spring season and was lower than the literature values for East Asian cities in the same season. This result shows that aging of organic aerosol particles proceeds during long-range transport from East Asia. In the Asian Pacific region, these pollutants are transported from East Asia in the winter-spring season, whereas clean air mass is transported from the Pacific Ocean in the summer-fall season.  相似文献   

The stability and origin of sodicgedrite in ultrahigh-temperature Mg-Al granulites: a case study from the Gondwana suture in southern India     

Tomohito Kanazawa  Toshiaki Tsunogae  Kei Sato  M. Santosh 《Contributions to Mineralogy and Petrology》2009,157(1):95-110

Mg-Al-rich rocks from the Palghat-Cauvery Shear Zone System (PCSZ) within the Gondwana suture zone in southern India contain sodicgedrite as one of the prograde to peak phases, stable during T = 900–990°C ultrahigh-temperature metamorphism. Gedrite in these samples is Mg-rich (Mg/[Fe + Mg] = X _Mg = 0.69–0.80) and shows wide variation in Na₂O content (1.4–2.3 wt.%, Na^A = 0.33–0.61 pfu). Gedrite adjacent to kyanite pseudomorph is in part mantled by garnet and cordierite. The gedrite proximal to garnet shows an increase in Na^A and Al^IV from the core (Na^A = 0.40–0.51 pfu, Al^IV = 1.6–1.9 pfu) to the rim (Na^A = 0.49–0.61 pfu, Al^IV = 2.0–2.2 pfu), suggesting the progress of the following dehydration reaction: Ged + Ky → Na-Ged + Grt + Crd + H₂O. This reaction suggests that, as the reactants broke down during the prograde stage, the remaining gedrite became enriched in Na to form sodicgedrite, which is regarded as a unique feature of high-grade rocks with Mg-Al-rich and K–Si-poor bulk chemistry. We carried out high-P-T experimental studies on natural sodicgedrite and the results indicate that gedrite and melt are stable phases at 12 kbar and 1,000°C. However, the product gedrite is Na-poor with only <0.13 wt.% Na₂O (Na^A = 0.015–0.034 pfu). In contrast, the matrix glass contains up to 8.5 wt.% Na₂O, suggesting that, with the progressive melting of the starting material, Na was partitioned into the melt rather than gedrite. The results therefore imply that the occurrence of sodicgedrite in the UHT rocks of the PCSZ is probably due to the low H₂O activity during peak P-T conditions that restricted extensive partial melting in these rocks, leaving Na partitioned into the solid phase (gedrite). The occurrence of abundant primary CO₂-rich fluid inclusions in this rock, which possibly infiltrated along the collisional suture during the final amalgamation of the Gondwana supercontinent, strengthens the inference of low water activity.  相似文献   

The geochemistry of volatile species in melt inclusions and sulfide minerals from Izu-Oshima volcano, Japan     

Kei Ikehata  Atsushi Yasuda  Kenji Notsu 《Mineralogy and Petrology》2010,99(1-2):143-152

Olivine-hosted melt inclusions in the O95 pyroclastic layer of Izu-Oshima volcano, Japan are basaltic to basaltic-andesitic in composition. The negative correlation between SiO₂ and H₂O in melt inclusions and reverse compositional zoning observed in olivine and other mineral phenocrysts is inferred to arise from mixing between a highly evolved and a less evolved magma. The latter is characterized by the highest S (0.15 wt.%) and H₂O (3.4 wt.%) concentrations among those described in reports of previous studies. The S⁶⁺/S_total ratios in melt inclusions were 0.64?–?0.73, suggesting a relatively high oxidation state (NNO + 0.87 at 1150°C). The presence of pyrrhotites, which are found only in titanomagnetite microlites, suggests that sulfide saturation occurred during microlite growth under at a sulfur fugacity (log fS₂) value of around + 0.5 for T = 1060°C. The groundmass glass compositions are more evolved (andesitic composition) than any melt inclusions containing high amounts of Cl (0.13 wt.%) but negligible H₂O (0.20 wt.%) and S (< 70 ppm), suggesting that Cl was retained in the magma, in contrast to S and H₂O, which degassed strongly during magma effusion.  相似文献   

Solubilities of nitrogen and noble gases in silicate melts under various oxygen fugacities: implications for the origin and degassing history of nitrogen and noble gases in the earth     

Akiko Miyazaki  Hajime Hiyagon  Kei Hirose 《Geochimica et cosmochimica acta》2004,68(2):387-401

Solubility experiments for nitrogen and noble gases (Ar and Ne) in silicate melts were conducted using two experimental configurations: one was conducted at 1 atmospheric pressure, T =1300°C and oxygen fugacity (fO₂) of IW + 0.9 (i.e., 0.9 log units higher than the iron-wüstite buffer) and the other at high pressures (P_total ∼ 2 × 10⁸ Pa), 1500°C and fO₂ ∼ IW + 6. For the former experiment, isotopically labeled-nitrogen (¹⁵N¹⁵N-enriched) was used to distinguish dissolved nitrogen from contaminating atmospheric or organic nitrogen and to examine dissolution mechanisms of nitrogen in silicate melts. The results obtained for the two series of experiments are consistent with each other, suggesting that Henry's law is satisfied for fN₂ of up to ∼250 atm (2.5 × 10⁷ Pa). The results are also consistent with our earlier results (Miyazaki et al., 1995) obtained at highly oxidizing conditions (fO₂ ∼ IW + 10). All these results support physical dissolution of nitrogen as N₂ molecules in silicate melts for fO₂ from ∼IW + 10 down to ∼IW. The observed solubility (Henry's constant) of nitrogen (3-5 × 10⁻⁹ mol/g/atm) is comparable to that of Ar (2-4 × 10⁻⁹ mol/g/atm), and much lower than that of Ne (11-14 × 10⁻⁹ mol/g/atm) at 1300°C. A preliminary experiment was also performed for partitioning of nitrogen and noble gases between clinopyroxene (cpx) and basaltic melt using a piston cylinder-type apparatus at 1.5 GPa and at 1270 to 1350°C. The obtained cpx/melt partition coefficient of nitrogen is 0.06, slightly lower than those of noble gases (∼0.1 for Ne to Xe), suggesting that nitrogen is as incompatible as or even slightly more incompatible than noble gases. The present results imply that a large nitrogen/Ar fractionation would not be produced by magmatic processes. Therefore, the two orders of magnitude difference between the N₂/³⁶Ar ratios in the Earth's atmosphere (∼10⁴) and that in the mantle (∼10⁶) must be explained by some other processes, such as incomplete segregation of metal blobs into the core and their later oxidation.  相似文献   

Application of a Simulation Model for the Formation of Methane Hydrate to the Nankai Trough and the Blake Ridge: Natural Examples of Two End-member Cases     

Kei Baba  Arata Katoh 《Resource Geology》2004,54(1):125-135

Abstract. Simulation experiments with a one-dimensional static model for formation of methane hydrate are used to demonstrate models of hydrate occurrence and its generation mechanism for two end-member cases. The simulation results compare well with experimental data for two natural examples (the Nankai Trough and the Blake Ridge).
At the MITI Nankai Trough wells, the hydrate occurrence is characterized by strongly hydrated sediments developing just above the BGHS. Such occurrence can be reproduced well by simulation in which the end-member case of upward advective fluid flow from below the BGHS is set. The strongly hydrated sediments is formed by oversaturated solution with free gas which directly enters the BGHS by the upward advective fluid flow. The recycling of dissociated methane of preexisting hydrate also contributes to the increase of hydrate saturation.
At the Site 997 in the Blake Ridge area, the hydrate occurrence is characterized by thick zone with poorly hydrated sediments and no hydrate zone developing above the hydrate zone. Such occurrence can be reproduced well by simulation in which the end-member case of in-situ biogenic production of methane in the sediment of methane hydrate zone is set. The distribution pattern of hydrate saturation is basically controlled by that of TOC. However, the hydrate concentration near the bottom of the hydrate zone is increased by the effect of recycling of dissociated methane of pre-existing hydrate. No hydrate zone expresses the geologic time needed until the local concentration of methane exceeds the solubility by gradual accumulation of in-situ biogenic methane with burial.  相似文献   

Book reviews     

S. J. Gibowicz  John W. Rudnicki  Vladimir Pinsky  Gary Mavko  William L. Power  A. V. Koloskov  Randall Lee Mackie  Yu. N. Korenkov  Kei Katsumata 《Pure and Applied Geophysics》1991,135(1):135-164

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