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21.
A pattern of slick streaks winding into a spiral, known as a spiral eddy, was identified in 5 images taken by the ERS-1/2
synthetic aperture radar (SAR) in Mutsu Bay (Japan); dynamic and kinematic models of these spiral eddies have been proposed.
Common characteristics of the five spiral eddies are: 1) an eddy diameter of about 15 km; 2) their location in the western
part of the bay; and 3) their cyclonic direction of rotation. Moreover, the wind conditions over the bay were common: prior
to acquiring the images, a strong easterly wind continued blowing for more than one day. The wind field on the bay is known
to be orographically steered and has strong windstress vorticity, which generates cyclonic circulation. The diameter and location
of the circulation simulated with a numerical ocean model corresponded well to those of the identified spiral eddies. Based
on these facts, we propose a dynamic model for the movement of a slick streak, and a kinematic model for the formation of
a spiral eddy. We have assumed calm air, a microlayer and seawater with a cyclonic circulation in the dynamic model. The balance
of forces is established in the microlayer among the frictional force from the seawater, the frictional force from the calm
air, the gravitational force, and the Coriolis force. As a result, the velocity vector of the microlayer deflects slightly
towards the center of the cyclonic circulation. We have assumed a point source of the microlayer in the kinematic model. The
shapes of a slick streak simulated with the models agree well with the identified patterns in the SAR images. 相似文献
22.
Wataru Takahashi Hiroshi Kawamura Takuo Omura Ken Furuya 《Journal of Oceanography》2009,65(5):647-656
A multi-spectral classification scheme is proposed to identify water with red tide(s) using satellite ocean color imagery
obtained by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The study area was the eastern Seto Inland Sea in Japan,
where serious red tides frequently occur. “Background Ocean Colors” (BOCs hereafter), or colors of water around a red tide
or those of the water before/after a red tide, are calculated as the monthly climatological average of normalized water-leaving
radiances (nLw) with 0.01 degree spatial resolution with SeaWiFS imagery. Criteria for detecting red-tide pixels are established
from analyses of characteristics of the nLws (in the 443, 490, 510, and 555 nm bands) anomalies from BOCs and the nLw spectra
together with the red-tide records in Osaka Bay. The proposed scheme can efficiently indicate the presence or absence of red
tides for independent match-ups with 83% accuracy. Additional validations of specific events indicate that the algorithm performed
well in the study area. These results suggest that the scheme is appropriate to detect red tides in the optically complex
coastal water of the eastern Seto Inland Sea. 相似文献
23.
Under strong surface wind forcing during winter, direct current observations in the northern Sea of Japan show the existence of strong near-inertial currents in the deep water that is characterized by the extremely homogeneous vertical structures of temperature and salinity. However, the mechanism generating internal waves in the deep water of the northern Sea of Japan has not been well understood. In this study, to clarify the dynamical link between the surface wind forcing and near-inertial currents in the deep water of the northern Sea of Japan, we drive a general circulation model taking into account realistic wind stress, ocean bottom and land topography. In the northern Sea of Japan, the numerical results show that vertically coherent horizontal currents with a speed of ~ 0.05 m s?1 are excited throughout the homogeneous deep water. A two-layer model successfully reproduces the pattern of the horizontal current velocities shown by the general circulation model, indicating that internal waves emanate westward from the northwestern coast of Japan through coastal adjustment to the strong wind forcing event and, while propagating into the ocean interior, they excite evanescent near-inertial response throughout the lower layer below the interface. 相似文献
24.
Tomohiro Nakamura Takahiro Toyoda Yoichi Ishikawa Toshiyuki Awaji 《Journal of Oceanography》2010,66(1):41-60
A steady quasi-geostrophic 2.5-layer model, forced by both Ekman pumping and a mass source/sink situated at the western boundary
has been constructed to investigate the effect of diapycnal transport due to convection in the Okhotsk Sea and tidal mixing
at the Kuril Straits on the intermediate layer in the North Pacific. The model illustrates a combined effect of the wind-driven
and mass-driven circulations. First, net mass input induces a “barotropic” mode inter-gyre flow along the western boundary
through the dynamical influence of Kelvin waves. This flow creates characteristic curves (geostrophic contours) that facilitate
inter-gyre communication through the western boundary layer from the location of the mass source to the subtropical gyre.
Due to the effect of wind-driven circulation, the offshore part turns eastward into the interior, encircles the outer rim
of the region (which would otherwise be the pool region in the absence of mass input), and then encounters the western boundary.
Eventually, the water fed into the lower layer flows mostly along this path and later flows away to the equatorial region.
Conversely, in the upper layer, water is fed from the equator to the subtropics, and to the subpolar interior region through
the western boundary current. The water then circulates along the outer rim and is absorbed into the mass sink. The model
is controlled mainly by three nondimensional parameters: (1) the ratio of net mass input rate to the maximum Sverdrup transport
(Q/T
Sv
max
), which affects the inter-gyre communication by altering the paths of geostrophic contours, (2) the ratio of a mass input
rate into the lower layer to that in total (Q
2/Q), which controls the vertical structure of the inter-gyre flow, and (3) the measure of the wind forcing effect relative to
the β effect, which determines the horizontal extent of the area influenced by the mass input. The other parameter regimes with
respect to Q/T
Sv
max
and Q
2/Q are also presented. 相似文献
25.
Mitsuhiko Hayashi Ichiro Tamura Osamu Shimomura Hiroshi Sawamoto Haruki Kawamura 《Physics and Chemistry of Minerals》1987,14(4):341-344
Néel temperature (Tm N of α-Fe2SiO4 (fayalite) was measured as a function of pressure by means of Mössbauer spectroscopy in the pressure range 0–16 Gpa. High pressure was generated using a clamp-type miniature diamond anvil cell which was inserted into a cryostat. The Néel temperature increased linearly with increasing pressure at a rate of dT N /dp=2.2±0.2 K/GPa. The result is discussed on the basis of the model proposed for the magnetic structure of fayalite by Santoro et al. (1966). The observed dT N /dp suggests that the superexchange interactions vary as the ?10/3 power of the volume while the volume dependence of the direct exchange interactions is positive and small. 相似文献
26.
We describe in detail the deformation structures and textures of a large-scale landslide body that developed in the Betto-dani
Valley in northern central Japan. We studied the shape-preferred orientation of clasts and clay flakes and the development
of internal shear planes within the slip zone of the landslide. The slip has an average rate of 5–10 cm/year under the overburden
pressure of approximately 1.6 MPa; these values are similar to those of the proto-decollement zone of the Nankai accretionary
prism in SW Japan. The anisotropy of magnetic susceptibility of samples obtained from the slip zone reveals that the long
axes of clay flakes define an imbricate structure. The slip was due to a long-term periodical creep, which occurs during the
thaw seasons with an average slip rate of 0.16–0.32 μm/min. During the creep, the long axes of grains including clay flakes
in the slip zone are developed from parallel to perpendicular to the slip direction. The observed textures provide a clue
to elucidate the deformation textures and process in the decollement zone of the Nankai prism. 相似文献
27.
Toshiyuki Masuzawa Nobuhiko Handa Hiroyuki Kitagawa Minoru Kusakabe 《Earth and Planetary Science Letters》1992,110(1-4):39-50
Two sandy sediment cores (Cores D227-120 and D380) were collected from inside a deep-sea giant clam (Calyptogena soyoae) community off Hatsushima Island, western Sagami Bay, central Japan (35°59.9′N, 139°13.6′E; 1160 m deep) and a muddy sediment core (Core D227-202) was obtained from outside the community by the submersibleShinkai 2000. The chloride concentration of the pore waters is constant vertically and sulfate reduction using sedimentary organic matter occurs in Core D227-202 (21 cm long). The chloride concentrations are lower by 7% at the 7.5–9 cm depth in Core D227-120 (9 cm long) and by 3% at the 11–12 cm depth in Core D380 (16 cm long) than those of the overlying bottom waters in the cores from inside of the community. Sulfate concentration decreases remarkably and dissolved inorganic carbon, alkalinity, ammonium-N, and hydrogen sulfide concentrations increase significantly with increasing depth in Core D380.δ34S values of sulfate ions increase from +20.5 to +35.3‰ andδ13C values of dissolved inorganic carbon decrease drastically from −7.0 to −45‰ with increasing depth from the top to the bottom of the core, although theδ13C values of the organic carbon of the sediments are−23.7 ± 0.9‰ in Core D380. These results indicate that sulfate reduction using methane is active within the sediments just beneath the living clams and that the hydrogen sulfide produced can be used by endosymbiotic sulfur oxidizing bacteria living in the gills ofC. soyoae in the community. 相似文献
28.
Apparent fracture toughness in Mode I of microcracking materials such as rocks under confining pressure is analyzed based
on a cohesive crack model. In rocks, the apparent fracture toughness for crack propagation varies with the confining pressure.
This study provides analytical solutions for the apparent fracture toughness using a cohesive crack model, which is a model
for the fracture process zone. The problem analyzed in this study is a fluid-driven fracture of a two-dimensional crack with
a cohesive zone under confining pressure. The size of the cohesive zone is assumed to be negligibly small in comparison to
the crack length. The analyses are performed for two types of cohesive stress distribution, namely the constant cohesive stress
(Dugdale model) and the linearly decreasing cohesive stress. Furthermore, the problem for a more general cohesive stress distribution
is analyzed based on the fracture energy concept. The analytical solutions are confirmed by comparing them with the results
of numerical computations performed using the body force method. The analytical solution suggests a substantial increase in
the apparent fracture toughness due to increased confining pressures, even if the size of the fracture process zone is small. 相似文献
29.
The Resonance Capacity Method is proposed for the earthquake response analysis of hysteretic structures. Resonance Capacity is a physical quantity of structures which is related to the hysteretic energy absorbed by structures in one cycle and is equated to the acceleration, velocity and displacement amplitudes α0, d0 and d0 of earthquake ground motions at resonance.1 According to the idealized trapezoidal approximation of earthquake ground motions in the logarithmic period–velocity plane as proposed by Veletsos and Newmark,8 the Resonance Capacity property applies in each period range, short, medium and long, where α0, v0 and d0 respectively are approximately constant. In the medium range of periods, the energy dissipated in hysteretic loops and the deformation amplitudes of a single-degree system with elasto–plastic force–deformation relationships are calculated for the case of El Centro 1940, 18 May earthquake, by this Resonance Capacity Method. The result is compared with results from conventional numerical response analyses obtained by Berg and Thomaides,14 Kato and Akiyama12 and Veletsos and Newmark,8 and the general agreement is seen to be good. Therefore, it may be possible to apply this Resonance Capacity Method over the entire range of periods. By means of this method the earthquake response analysis of hysteretic systems can be performed easily, and the hysteretic energy and fatigue characteristics of structures may be taken into account directly, up to the point of fracture. 相似文献
30.
Toshiyuki Wakatsuki Hisao Furukawa Kazutake Kyuma 《Geochimica et cosmochimica acta》1977,41(7):891-902
Sixteen alluvial and terrace soils from Japan and Thailand were separated into six fractions ; an amorphous sesquioxide and combined organic matter fraction, crystalline sesquioxides, clay, silt, fine sand and coarse sand. Content of ten major and minor elements in these six fractions was analyzed; SiO2, A12O3, Fe2O3, MgO, CaO, K2O, TiO2, Rb2O and SrO were determined by X-ray fluorescence spectrometry, and Na2O was determined by neutron activation analysis. The clay, silt, fine sand and coarse sand mineralogy were estimated semi-quantitatively by X-ray diffraction methods.We propose three indices of geochemical maturity for the soils and test their usefulness as measures of the degree of weathering. Three concomitant factors are proposed to measure the relative resistate, hydrolyzate and oxidate nature of the major elements in the soils. 相似文献