Estimating snow distribution over a large area and its application for water resources     

So Kazama  Hirokazu Izumi  Priyantha Ranjan Sarukkalige  Takayuki Nasu  Masaki Sawamoto 《水文研究》2008,22(13):2315-2324

The spatial and temporal distribution of the snow water equivalent (SWE), snow density and snow depth were estimated by a method combining remote sensing technology and degree‐day techniques over a study area of 370 000 km². The advantages of this simulation model are its simplicity and the availability of degree‐day parameters, which can be successively evaluated by referring to snow area maps created from satellite images. This simulation worked very well for estimating SWE and helped to separate the areas of thin snow cover from heavier snowfall. However, shallow snow in warm regions led to some misjudgments in the snow area maps because of the time lag between when the satellite image was acquired and the simulation itself. Vulnerable areas, where a large variation in the amount of snow affects people's life, could be identified from the differences between heavy and light snow years. This vulnerability stems from a predicted lack of irrigation water for rice production caused by future climate change. The model developed in this study has the potential to contribute to water management activities and decision‐making processes when considering necessary adaptations to future climate change. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Data assimilation using the particle filter for identifying the elasto‐plastic material properties of geomaterials     

Akira Murakami  Takayuki Shuku  Shin‐ichi Nishimura  Kazunori Fujisawa  Kazuyuki Nakamura 《国际地质力学数值与分析法杂志》2013,37(11):1642-1669

A computational method, incorporating the finite element model (FEM) into data assimilation using the particle filter, is presented for identifying elasto‐plastic material properties based on sequential measurements under the known changing traction boundary conditions to overcome some difficulties in identifying the parameters for elasto‐plastic problems from which the existing inverse analysis strategies have suffered. A soil–water coupled problem, which uses the elasto‐plastic constitutive model, is dealt with as the geotechnical application. Measured data on the settlement and the pore pressure are obtained from a synthetic FEM computation as the forward problem under the known parameters to be identified for both the element tests and the ground behavior during the embankment construction sequence. Parameter identification for elasto‐plastic problems, such as soil behavior, should be made by considering the measurements of deformation and/or pore pressure step by step from the initial stage of construction and throughout the deformation history under the changing traction boundary conditions because of the embankment or the excavation because the ground behavior is highly dependent on the loading history. Thus, it appears that sequential data assimilation techniques, such as the particle filter, are the preferable tools that can provide estimates of the state variables, that is, deformation, pore pressure, and unknown parameters, for the constitutive model in geotechnical practice. The present paper discusses the priority of the particle filter in its application to initial/boundary value problems for elasto‐plastic materials and demonstrates a couple of numerical examples. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Ion microprobe analyses of oxygen three‐isotope ratios of chondrules from the Sayh al Uhaymir 290 CH chondrite using a multiple‐hole disk     

Daisuke NAKASHIMA  Takayuki USHIKUBO  Rudraswami N. GOWDA  Noriko T. KITA  John W. VALLEY  Keisuke NAGAO 《Meteoritics & planetary science》2011,46(6):857-874

Abstract– The ion microprobe is the only technique capable of determining high‐precision stable isotope ratios in individual tiny extraterrestrial particles (≤100 μm in diameter), but these small samples present special analytical challenges. We produced a new sample holder disk with multiple holes (three holes and seven holes), in which epoxy disks containing a single unknown sample and a standard grain are cast and polished. Performance tests for oxygen two‐isotope analyses using San Carlos olivine standard grains show that the new multiple‐hole disks allow accurate analysis of tiny particles if the particles are located within the 500 μm and 1 mm radius of the center of holes for seven‐hole and three‐hole disks, respectively. Using the new seven‐hole disk, oxygen three‐isotope ratios of eight magnesian cryptocrystalline chondrules (approximately 100 μm in diameter) from the Sayh al Uhaymir (SaU) 290 CH chondrite were analyzed by ion microprobe at the University of Wisconsin. Five out of eight chondrules have nearly identical oxygen isotope ratios (Δ¹⁷O = ?2.2 ± 0.6‰; 2SD), which is consistent with those of magnesian cryptocrystalline chondrules in CH/CB and CB chondrites, suggesting a genetic relationship, i.e., formation by a common (possibly impact) heating event. The other three chondrules have distinct oxygen isotope ratios (Δ¹⁷O values from ?6.4‰ to +2.2‰). Given that similar variation in Δ¹⁷O values was observed in type I porphyritic chondrules in a CH/CB chondrite, the three chondrules may have formed in the solar nebula, similar to the type I porphyritic chondrules.  相似文献   

Temporal changes in electrical resistivity at Sakurajima volcano from continuous magnetotelluric observations     

Koki Aizawa  Wataru Kanda  Yasuo Ogawa  Masato Iguchi  Akihiko Yokoo  Hiroshi Yakiwara  Takayuki Sugano 《Journal of Volcanology and Geothermal Research》2011,199(1-2):165-175

Continuous magnetotelluric (MT) measurements were conducted from May 2008 to July 2009 at Sakurajima, one of the most active volcanoes in Japan. Two observation sites were established at locations 3.3 km east and 3 km west–northwest of the summit crater. At both observation sites, the high-quality component of the impedance tensor (Zyx) showed variations in apparent resistivity of approximately ± 20% and phase change of ± 2°, which continued for 20–180 days in the frequency range between 320 and 4 Hz. The start of the period of changes in apparent resistivity approximately coincided with the start of uplift in the direction of the summit crater, as observed by a tiltmeter, which is one of the most reliable pieces of equipment with which to detect magma intrusion beneath a volcano. A 2D inversion of MT impedance suggests that the resistivity change occurred at a depth around sea level. One of the possible implications of the present finding is that the degassed volatiles migrated not only vertically through the conduit but also laterally through a fracture network, mixing with shallow groundwater beneath sea level and thereby causing the observed resistivity change.  相似文献   

Recognition of an Early Triassic accretionary complex in the Nedamo Belt of the Kitakami Massif,Northeast Japan: New evidence for correlation with Southwest Japan     

Takayuki Uchino 《Island Arc》2021,30(1):e12397

The Kitakami Massif of the Tohoku district, Northeast Japan, consists mainly of the South Kitakami Belt (Silurian–Cretaceous forearc shallow-marine sediments, granitoids, and forearc ophiolite) and the North Kitakami Belt (a Jurassic accretionary complex). The Nedamo Belt (a Carboniferous accretionary complex) occurs as a small unit between those two belts. An accretionary unit in the Nedamo Belt is lithologically divided into the Early Carboniferous Tsunatori Unit and the age-unknown Takinosawa Unit. In order to constrain the accretionary age of the Takinosawa Unit, detrital zircon U–Pb dating was conducted. The new data revealed that the youngest cluster ages from sandstone and tuffaceous rock are 257–248 Ma and 288–281 Ma, respectively. The Early Triassic depositional age of the sandstone may correspond to a period of intense magmatic activity in the eastern margin of the paleo-Asian continent. A 30–40 my interval between the youngest cluster ages of the sandstone and the tuffaceous rock can be explained by the absence of syn-sedimentary zircon in the tuffaceous rock. The new detrital zircon data suggest that the Takinosawa Unit can be distinguished as an Early Triassic accretionary complex distinct from the Early Carboniferous Tsunatori Unit. This recognition establishes a long-duration northeastward younging polarity of accretionary units, from the Carboniferous to Early Cretaceous, in the northern Kitakami Massif. Lithological features and detrital zircon spectra suggest that the Early Triassic Takinosawa Unit in the Nedamo Belt is comparable with the Hisone and Shingai units in the Kurosegawa Belt in Shikoku. The existence of this Early Triassic accretionary complex strongly supports a pre-Jurassic geotectonic correlation and similarity between Southwest and Northeast Japan.  相似文献   

Uniformly mantle-like δ<Superscript>18</Superscript>O in zircons from oceanic plagiogranites and gabbros   总被引：1，自引：1，他引：0  

Craig B. Grimes  Takayuki Ushikubo  Barbara E. John  John W. Valley 《Contributions to Mineralogy and Petrology》2011,161(1):13-33

Lower ocean crust is primarily gabbroic, although 1–2% felsic igneous rocks that are referred to collectively as plagiogranites occur locally. Recent experimental evidence suggests that plagiogranite magmas can form by hydrous partial melting of gabbro triggered by seawater-derived fluids, and thus they may indicate early, high-temperature hydrothermal fluid circulation. To explore seawater–rock interaction prior to and during the genesis of plagiogranite and other late-stage magmas, oxygen-isotope ratios preserved in igneous zircon have been measured by ion microprobe. A total of 197 zircons from 43 plagiogranite, evolved gabbro, and hydrothermally altered fault rock samples have been analyzed. Samples originate primarily from drill core acquired during Ocean Drilling Program and Integrated Ocean Drilling Program operations near the Mid-Atlantic and Southwest Indian Ridges. With the exception of rare, distinctively luminescent rims, all zircons from ocean crust record remarkably uniform δ¹⁸O with an average value of 5.2 ± 0.5‰ (2SD). The average δ¹⁸O(Zrc) would be in magmatic equilibrium with unaltered MORB [δ¹⁸O(WR) ~ 5.6–5.7‰], and is consistent with the previously determined value for equilibrium with the mantle. The narrow range of measured δ¹⁸O values is predicted for zircon crystallization from variable parent melt compositions and temperatures in a closed system, and provides no indication of any interactions between altered rocks or seawater and the evolved parent melts. If plagiogranite forms by hydrous partial melting, the uniform mantle-like δ¹⁸O(Zrc) requires melting and zircon crystallization prior to significant amounts of water–rock interactions that alter the protolith δ¹⁸O. Zircons from ocean crust have been proposed as a tectonic analog for >3.9 Ga detrital zircons from the earliest (Hadean) Earth by multiple workers. However, zircons from ocean crust are readily distinguished geochemically from zircons formed in continental crustal environments. Many of the >3.9 Ga zircons have mildly elevated δ¹⁸O (6.0–7.5‰), but such values have not been identified in any zircons from the large sample suite examined here. The difference in δ¹⁸O, in combination with newly acquired lithium concentrations and published trace element data, clearly shows that the >3.9 Ga detrital zircons did not originate by processes analogous to those in modern mid-ocean ridge settings.  相似文献   

Mg and Si isotopic fractionation patterns in types B1 and B2 CAIs: Implications for formation under different nebular conditions     

Emma S. Bullock  Kim B. Knight  Frank M. Richter  Noriko T. Kita  Takayuki Ushikubo  Glenn J. MacPherson  Andrew M. Davis  Ruslan A. Mendybaev 《Meteoritics & planetary science》2013,48(8):1440-1458

Magnesium and silicon isotopic profiles across melilite grains in two type B1 and two type B2 calcium‐aluminum‐rich inclusions (CAIs) reveal differing but constant enrichments in heavy isotopes everywhere except ≤1000 μm from the CAI margins. There is no close correlation in the B1s or the B2s between isotopic composition and åkermanite content of the melilite, a measure of progressive igneous crystallization, yet such a correlation might be expected in a type B2: without a melilite mantle (as in B1s) to seal the interior off and prevent further evaporation, the melt would have maintained communication with the external gas. These observations indicate a model in which B1s and B2s solidified under differing conditions. The B2s solidified under lower hydrogen pressures ( ≤ 10^?4 – 10^?5 bars) than did B1s ( > 10^?4 bars), so surface volatilization was slower in the B2s and internal chemical and isotopic equilibrium was maintained over the interval of melilite crystallization. The outermost zones of the CAIs (≤1000 μm from the edge) are not consistently enriched in heavy isotopes relative to the interiors, as might be expected from diffusion‐limited surface evaporation of the melt. In all cases, the magnesium in the CAI margins is lighter than in the interiors. In one case, silicon in the margin also is lighter, but locally in some CAIs, it is isotopically heavier near the surface. If melt evaporation played a role in the formation of these outer zones, a later event in many cases caused isotopic re‐equilibration with an external and isotopically near‐normal reservoir.  相似文献   

Fall,classification, and exposure history of the Mifflin L5 chondrite     

Noriko T. Kita  Kees C. Welten  John W. Valley  Michael J. Spicuzza  Daisuke Nakashima  Travis J. Tenner  Takayuki Ushikubo  Glenn J. MacPherson  Linda Welzenbach  Philipp R. Heck  Andrew M. Davis  Matthias M. M. Meier  Rainer Wieler  Marc W. Caffee  Matthias Laubenstein  Kunihiko Nishiizumi 《Meteoritics & planetary science》2013,48(4):641-655

The Mifflin meteorite fell on the night of April 14, 2010, in southwestern Wisconsin. A bright fireball was observed throughout a wide area of the midwestern United States. The petrography, mineral compositions, and oxygen isotope ratios indicate that the meteorite is a L5 chondrite fragmental breccia with light/dark structure. The meteorite shows a low shock stage of S2, although some shock‐melted veins are present. The U,Th‐He age is 0.7 Ga, and the K‐Ar age is 1.8 Ga, indicating that Mifflin might have been heated at the time of the 470 Ma L‐chondrite parent body breakup and that U, Th‐He, and K‐Ar ages were partially reset. The cosmogenic radionuclide data indicate that Mifflin was exposed to cosmic rays while its radius was 30–65 cm. Assuming this exposure geometry, a cosmic‐ray exposure age of 25 ± 3 Ma is calculated from cosmogenic noble gas concentrations. The low ²²Ne/²¹Ne ratio may, however, indicate a two‐stage exposure with a longer first‐stage exposure at high shielding. Mifflin is unusual in having a low radiogenic gas content combined with a low shock stage and no evidence of late stage annealing; this inconsistency remains unexplained.  相似文献   

Evolution of protoplanetary disk inferred from 26Al chronology of individual chondrules     

Noriko T. KITA  Takayuki USHIKUBO 《Meteoritics & planetary science》2012,47(7):1108-1119

Abstract– We review the ²⁶Al ages of chondrules in various type 3.0 chondrites. The ²⁶Al ages of chondrules are 1–3 Myr after calcium‐aluminum‐rich inclusion (CAI) for LL3.0, CO3.0, and Acfer 094 (Ungrouped C 3.0). Available data for chondrules in CR chondrites indicate that many chondrules are relatively younger (≥3 Myr), although data from chondrules in CR3.0 are not yet available to confirm their younger ages. The total ranges for the ²⁶Al ages of chondrules in a single chondrite group are more than 0.5–1 Myr. However, most chondrules show relatively narrow range of ages in a single chondrite group (0.2–0.4 Myr, 1 SD), which might be short enough to preserve the group‐specific chemical and isotope signatures against radial diffusion of solid in the disk. Distinct oxygen isotope reservoirs might exist in the protoplanetary disk simultaneously, which could be spatially separated.  相似文献   

A natural symmetrization for the plummer potential     

Takayuki R. Saitoh  Junichiro Makino 《New Astronomy》2012,17(2):76-81

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