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21.
Gas was sampled regionally, including by drilling into faults, in the South Kanto gas-field around Tokyo Bay, Japan. Gas samples were collected from cores in a gas sampling container immediately after drilling. A value of δ13C1 = −44.3‰ was obtained for gas in the container and δ13C1 = −36.3‰ for seeping gas in a fault zone. However, typical CH4 in this dissolved-in-water gas-field is mainly depleted in 13C, and δ13C1 values range from −66‰ to −68‰ owing to microbial degradation of organic material. 13C-rich CH4 is so far uncommon in the South Kanto gas-field. Seepages were observed from the surface along the north–south fault zone. The natural gas is stored below the sandstone layer by impermeable mudstone underlying the boundary at a depth of 30 m. Gas seepages were not observed below a depth of 40 m. Gas rises along the fault zone dissolved-in-groundwater up to the shallow region and then separates from the groundwater. 13C-rich CH4 (adsorbed CH4) was found to have desorbed from drilled mudstone core samples taken at depths of 1400–1900 m in the main gas-production strata. Similarly, 13C-rich CH4 was found in black shale overlying the oceanic crust forming part of a sedimentary accretionary prism underling the Tokyo region. It also appears in the spring-water of spa wells, originating at a depth of 1200–1500 m along a tectonic line. Methane generated by microbial degradation of organic material through CO2 reduction in the South Kanto gas-field mainly originates as biogenic gas mixed with a small amount of 13C-rich CH4, derived from thermogenic gas without oil components in strata. It is assumed that 12C-rich CH4 is easily detached from core or pore water through gas production, whereas 13C-rich CH4 is strongly adsorbed on the surfaces of particles. The 13C-rich CH4 rises along the major tectonic line or up the 50 m wide normal fault zone from relatively deep sources in the Kanto region. 相似文献
22.
Badri Bhakta Shrestha Hajime Nakagawa Kenji Kawaike Yasuyuki Baba Hao Zhang 《Natural Hazards》2012,61(2):577-602
Experience shows that debris flows containing large woody debris (driftwood) can be more damaging than debris flows without
driftwood. In this study, the deposition process of debris flows carrying driftwood was investigated using numerical simulations
and flume experiments. Debris-flow trapping due to driftwood jamming in a slit-check dam was also investigated. A numerical
model was developed with an interacting combination of Eulerian expression of the debris flow and Lagrangian expression of
the driftwood, in which the fluctuating coordinates and rotation of the driftwood were treated stochastically. The calculated
shapes and thicknesses of a debris-flow fan and the positions and orientations of the deposited driftwood on a debris-flow
fan were consistent with experimental flume results. The jamming of driftwood in a slit-check dam was evaluated based on geometry
and probability. The simulated results of outflow discharge and the proportion of driftwood passed through the slit-check
dam also agreed with the experimental results. 相似文献
23.
Duong Du Bui Akira Kawamura Thanh Ngoc Tong Hideo Amaguchi Naoko Nakagawa 《Hydrogeology Journal》2012,20(8):1635-1650
A groundwater-monitoring network has been in operation in the Red River Delta, Vietnam, since 1995. Trends in groundwater level (1995?C2009) in 57 wells in the Holocene unconfined aquifer and 63 wells in the Pleistocene confined aquifer were determined by applying the non-parametric Mann-Kendall trend test and Sen??s slope estimator. At each well, 17 time series (e.g. annual, seasonal, monthly), computed from the original data, were analyzed. Analysis of the annual groundwater-level means revealed that 35?% of the wells in the unconfined aquifer showed downward trends, while about 21?% showed upward trends. On the other hand, confined-aquifer groundwater levels experienced downward trends in almost all locations. Spatial distributions of trends indicated that the strongly declining trends (>0.3?m/year) were mainly found in urban areas around Hanoi where there is intensive abstraction of groundwater. Although the trend results for most of the 17 time series at a given well were quite similar, different trend patterns were detected in several. The findings reflect unsustainable groundwater development and the importance of maintaining groundwater monitoring and a database in the Delta, particularly in urban areas. 相似文献
24.
Norihisa?UsuiEmail author Shiro?Ishizaki Yosuke?Fujii Masafumi?Kamachi 《Journal of Oceanography》2011,67(3):253-262
We assess validity of a Gaussian error assumption, the basic assumption in data assimilation theory, and propose two kinds
of constraints regarding non-Gaussian statistics. In the mixed water region (MWR) off the east coast of Japan exhibiting complicated
frontal structures, a probability density function (PDF) of subsurface temperature shows double peaks corresponding to the
Kuroshio and Oyashio waters. The complicated frontal structures characterized by the temperature PDF sometimes cause large
innovations, bringing about a non-Gaussianity of errors. It is also revealed that assimilated results with a standard three-dimensional
variational (3DVAR) scheme have some issues in MWR, arising from the non-Gaussianity of errors. The Oyashio water sometimes
becomes unrealistically cold. The double peaks seen in the observed temperature PDF are too smoothed. To improve the assimilated
field in MWR, we introduce two kinds of constraints, J
c1 and J
c2, which model the observed temperature PDF. The constraint J
c1 prevents the unrealistically cold Oyashio water, and J
c2 intends to reproduce the double peaks. The assimilated fields are significantly improved by using these constraints. The
constraint J
c1 effectively reduces the unrealistically cold Oyashio water. The double peaks in the observed temperature PDF are successfully
reproduced by J
c2. In addition, not only subsurface temperature but also whole level temperature and salinity (T–S) fields are improved by
adopting J
c1 and J
c2 to a multivariate 3DVAR scheme with vertical coupled T–S empirical orthogonal function modes. 相似文献
25.
By using the Euler-Lagrangian method, we examine water movements within the layer of minimum oxygen concentration and estimate local oxygen consumption rates for 15 regions of the global ocean. To do this, a number of labeled particles (which represent water parcels) are deployed at the center of a grid with 15 depth levels and tracked backward in time for 50 years in a three-dimensional velocity field. We assume that a particle picks up oxygen when it encounters the point of maximum oxygen concentration along the 50 years segment of its path. We introduce a contribution rate from waters distributed throughout the global ocean to the oxygen concentration of a local layer under consideration. Water parcels which are assumed to pick up oxygen within the oxygen minimum layer of an oceanic region under consideration make a very small contribution to the overall oxygen concentration of this layer. In addition, these parcels move out of the layer and water parcels from the upper layers take their place. The averaged Lagrangian local oxygen consumption rate is 0.033 ml/l/yr for the depth of the oxygen minimum layer, 0.20 ml/l/yr at 100 m depth (euphotic layer), 0.043 ml/l/yr for layers from 150 m to 800 m depth and 0.012 ml/l/yr for deep layers from 800 m to 3000 m. The present Lagrangian numerical experiment produces a maximum difference between observed and calculated concentrations of oxygen and, therefore, a maximum oxygen consumption rate. Although the present method has an ambiguity as to how oxygen is picked up, we nevertheless were able to identify regions in which the water parcels pick up oxygen of maximum concentration. We found that the South Equatorial Current (SEC) transports oxygen of higher concentration to the middle latitude regions of both the North Atlantic and the North Pacific across the equator. 相似文献
26.
Yozo Kudo Osam Sano Naokuni Murashige Yoshiaki Mizuta Koji Nakagawa 《Pure and Applied Geophysics》1992,138(4):641-656
The double-torsion test using Aji granite was carried out to investigate the interaction between stress-induced crack path and mineral grains. Crack velocities were controlled at range 10–7 m/s to 10–1 m/s. After the stressed specimens were dyed, we checked the crack path by thin section analysis, using an optical microscope. The stress-induced crack path was divided into two types, transgranular and intergranular cracks, and each path was subdivided with respect to mineral grains. In spite of the extensive range of crack velocities, the ratios between the transgranular and intergranular crack lengths did not change. The crack paths were all jagged, and often showed detour around the grain boundary when faced with obstacles like hard grains or preexisting cracks. That is to say, quartz grain played an important role as an obstacle. Feldspar grain could change the crack path because of its cleavage plane. Biolite grain had a serious effect on the path even if its constitution ratio is very small. Fractal dimensions of the crack paths were calculated by three methods, as indicators of surface roughness. The fractal dimensions were shown in a slight trend with the change of crack velocity. This trend can be explained from the point of limited cracking rate in stress corrosion. 相似文献
27.
A model of a coronal region of enhanced Fexv and Fexvi emission is developed and its energy balance is examined using extreme ultraviolet observations from OSO-7 together with calculations of possible force-free coronal magnetic field configurations. The coronal emissions overlying the photospheric boundary between regions of opposite magnetic polarity are found to be associated with generally non-potential (current-carrying) magnetic fields in the forms of arches with footpoints in regions of opposite polarity. The orientation of these arches relative to the neutral line changes with degree of ionization of the emitting ion (which we infer from our limb observations to be a function of height) and may be evidence of differing electric currents along various field lines. The appearance of a coronal arch, seen side-on, can conveniently be represented by a parabola and a detailed analysis (Appendix) shows this to be a realistic approximation that should be generally useful in analyzing two-dimensional pictures of coronal structures. Applying this analysis to the most prominent coronal region observed in the radiations of Fexv and Fexvi, we find a maximum in the electron temperature, T e , of 2.6 × 106K at the top of arches whose heights are 20000–40000 km and whose footpoints are separated by ≈ 100000 km. A temperature gradient of ▽T e ≈5 × 10-5K cm-1 is found in this coronal structure. Radiative losses are typically fifteen times greater than conductive losses and the energy deposition required to maintain the coronal feature is nearly uniformly distributed along its length. 相似文献
28.
Which is more important for tropical cyclone (TC) intensity and intensification, sea surface temperature (SST) or tropical cyclone heat potential (TCHP)? Investigations using best-track TC central pressures, TRMM/TMI three-day mean SST data, and an estimated TCHP based on oceanic reanalysis data from 1998 to 2004, show that the central pressure is more closely related to TCHP accumulated from TC formation to its mature stages than to the accumulated SST and its duration. From an oceanic environmental viewpoint, a rapid deepening of TC central pressure occurs when TCHP is relatively high on a basin scale, while composite distributions of TCHP, vertical wind shear, lower tropospheric relative humidity, and wind speed occurring in cases of rapid intensification are different for each TC season. In order to explore the influence of TCHP on TC intensity and intensification, analyses using both oceanic reanalysis data and the results of numerical simulations based on an ocean general circulation model are performed for the cases of Typhoons Chaba (2004) and Songda (2004), which took similar tracks. The decrease in TCHP due to the passage of Chaba led to the suppression of Songda’s intensity at the mature stage, while Songda maintained its intensity for a relatively long time because induced near-inertial currents due to the passage of Chaba reproduced anticyclonic warm eddies appearing on the leftside of Chaba’s track before Songda passed by. This type of intensity-sustenance process caused by the passage of a preceding TC is often found in El Niño years. These results suggest that TCHP, but not SST, plays an important role in TC intensity and its intensification. 相似文献
29.
Masanori Konda Norihisa Imasato Katsuya Nishi Takashi Toda 《Journal of Oceanography》1994,50(1):17-30
The sea surface emissivity in the infrared region is determined on the basis of data analyses. Net radiation, surface irradiance and other oceanographical and meteorological variables are measured throughout most of the year at the oceanographical observatory tower in Tanabe Bay, Japan. We have found that 0.984±0.004 is a reliable emissivity value from the night time data. Surface emission radiates not from the subsurface water but from the sea surface. The thermal skin layer on the sea surface, however, is disturbed and disappears under high wind speed over 5 m/s through the analyses of the radiation observation using the emissivity value of 0.984. Under low wind speed, the sea surface can be cooler or warmer than the subsurface due to overlying thermal conditions and the skin layer can be neutral as the transient process between them. By using an emissivity value of 0.984, the temperature difference between the sea surface temperature and the temperature determined from surface irradiance that has been reported in the satellite data analyses is found to be reduced by half. 相似文献
30.
Norihisa Imasato 《Journal of Oceanography》1976,32(1):21-32
The development process of wind-waves of which spectral peak distributes from 0.6 cps to 9.3 cps will be discussed on the basis of the wind tunnel experiments and of the field observations performed at Lake Biwa. The characteristics of power and slope spectra are here presented. The development process of these wind-waves is characterized by three stages;i.e. initial-wavelets, transition stage and sea-waves. In the wind tunnel experiments, the transition from the stage of the initial-wavelets to the transition stage occurs when the wave spectral peak arrives at the line 6.40×10–4
k
–2cm2·sec (wherek is wave number) or when the slope spectral density at the frequencyf
max becomes larger than 6.40×10–4 sec. In the stage of sea-waves, the component wave of a wave-spectral peak is steepest in the component waves. And the wave spectral peak develops along the line 1.02×102
f
–6 cm2·sec (wheref is the frequency corresponding to the wave numberk) untill it reaches the line 33.3f
–4cm2·sec, and thereafter develops along the latter line, which indicates the constant density of slope spectrum. It is suggested that the nonlinearity of wind-waves must become stronger as wind-waves develop. The effective momentum flux
ws
from the air flow to wind-waves in this stage is evaluated to be about 49% of the total stress
0. 相似文献