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261.
Kozo Yoshida 《Progress in Oceanography》1980,9(2):83-131
A simple three-dimensional model of a time-dependent coastal upwelling is discussed for time scales of several days to a week, with the linear, two-layer, flat-bottom and approximation. Emphasis is placed on the effects of longshore scales determined by the longshore variabilities in the wind stress distributions. The responses of the inshore motions are shown to depend critically on the longshore scales. For a certain wide range of the scales, the system reveals dominantly baroclinic responses and a full development of the poleward coastal undercurrent without β effect. Somewhat detailed discussions are given on the coastal upwelling, the coastal jet and the poleward undercurrent, which are interpreted simply as the orbital velocities of the forced Kelvin-type waves. 相似文献
262.
Examined here is a hypothetical idea of the splitting of the subtropical gyre in the western North Pacific on the basis of two independent sources of data,i.e., the long-term mean geopotential-anomaly data compiled by the Japanese Oceanographic Data Center and the synoptic hydrographic (STD) data taken by the Hakuho Maru in the source region of the Kuroshio and the Subtropical Countercurrent in the period February and March 1974. Both of the synoptic and the long-term mean dynamic-topographic maps reveal three major ridges, which indicate that the western subtropical gyre is split into three subgyres. Each subgyre is made up of the pair of currents, the Kuroshio and the Kuroshio Countercurrent, the Subtropical Countercurrent and a westward flow lying just south of the Countercurrent (18°N–21°N), and the northern part of the North Fquatorial Current and an eastward flow at around 18°N. The subgyres are more or less composed of a train of anticyclonic eddies with meridional scales of between 300 and 600 km, so that the volume transport of the subgyres varies by a factor of two or more from section to section. The upper-water characteristics also support the splitting of the subtropical gyre; the water characteristics are fairly uniform within each subgyre, but markedly different between them. The northern rim of each subgyre appears as a sharp density front accompanied by an eastward flow. The bifurcations of the sharp density fronts across the western boundary current indicate that the major part of the surface waters in the North Equatorial Countercurrent is not brought into the Kuroshio. The western boundary current appears as a continuous feature of high speed, but the waters transported change discontinuously at some places. 相似文献
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On the basis of the results confirmed in the new volume Kuroshio, a figure is presented on subsurface temperature arranged chronologically for the selected one-degree square to clearly document the bimodal state of the Kuroshio in this area. To extend this analysis of the state further into the non-documented past, a preliminary survey is attempted with the data on air and sea-temperatures at Hachijojima of these 45 years. As may be anticipated, those data are found to bear little in-phase correlation with the Cold Eddy, though they might prove useful after further analysis. Some ideas of analyzing tree-rings on Hachijojima and shallow sea sediments are also discussed in this connection. 相似文献
265.
Hidekuni Kuroki Hidemi M ItoAkio Yoshida 《Physics of the Earth and Planetary Interiors》2003,135(4):231-252
Using a 3D simulation model with a rate- and state-dependent friction law, Kuroki et al. (2002) discussed a process of a hypothetical great earthquake in the Tokai region, where the Philippine Sea plate subducts beneath the Eurasian plate. One of the main concerns was characteristic changes in volumetric strain and displacement on the ground surface which are caused by the evolution of the coupling between the two plates, i.e. evolution of a strongly coupled region between the plates which results in a preslip of the earthquake.In the present paper we discuss other observable phenomena which might help us to identify the stage of the coupling. The preslip of the earthquake could be more effectively detected by using full information about the change of strain rather than volumetric strain alone; the change in rotation angle of principal strain axes should amount to several tens of degrees while the order of the change in volumetric strain is 10−8 to 10−7 for 1 day before the earthquake. The spatial pattern of the displacement field on the ground surface provides us with information on the intermediate-term precursory changes in the plate coupling. Information given by micro-earthquakes is less direct. The seismicity should change considerably when a highly shear-stressed ring on the plate interface passes nearby, and ups and downs of seismicity rate will be estimated by Coulomb failure stress. On the other hand, focal mechanisms are rather insensitive to the progress of plate subduction. The changes may be not significant even at the time of the preslip. The interplate coupling yields a stress field that should produce reverse fault type mechanisms, but the stress field is modulated by a curved shape of the plate interface. Superposition of a regional tectonic stress to this field explains observed spatial distribution of focal mechanisms in the Tokai region which involve large strike-slip components. 相似文献
266.
This paper proposes a semiactive control system to reduce the coupled lateral and torsional motions in asymmetric buildings subjected to horizontal seismic excitations. Magnetorheological (MR) dampers are applied as semiactive control devices and the control input determination is based on a clipped‐optimal control algorithm which uses absolute acceleration feedback. The performance of this method is studied experimentally using a 2‐story building model with an asymmetric stiffness distribution. An automated system identification methodology is implemented to develop a control‐oriented model which has the natural frequencies observed in the experimental system. The parameters for the MR damper model are identified using experimental data to develop an integrated model of the structure and MR dampers. To demonstrate the performance of this control system on the experimental structure, a shake table is used to reproduce an El Centro 1940 N–S earthquake as well as a random white noise excitation. The responses for the proposed control system are compared to those of passive control cases in which a constant voltage is applied to the MR damper. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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270.
Boron isotopic composition of fumarolic condensates and sassolites from Satsuma Iwo-jima,Japan 总被引:1,自引:0,他引:1
Tadao Kanzaki Minoru Yoshida Masao Nomura Hidetake Kakihana Takejiro Ozawa 《Geochimica et cosmochimica acta》1979,43(11):1859-1863
11B/10B ratios of the high temperature fumarolic gases (>465°C) of this island were found to be constant within the limits of experimental error (11B/10B = 4.066). This value may represent the 11B/10B ratio of boron in the andesite magma. 11B/10B ratios of the low temperature fumarolic gases (<235°C) were found to vary from 4.053 to 4.077. 11B/10B ratios of some sassolites were approximately equal to that of the fumarolic condensates and the other ones were slightly enriched in 10B compared to the fumarolic condensates. 相似文献