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排序方式: 共有145条查询结果,搜索用时 31 毫秒
51.
Akio Ishida Kisaburo Nakata Shigeaki Aoki Hiroshi Kutsukake Michio J. Kishi Masahisa Kubota 《Journal of Oceanography》2001,57(4):433-450
Distributions and characteristics of water mass and chlorofluorocarbons (CFCs) in the North Pacific are investigated by using
a General Circulation Model (GCM). The anthropogenic CO2 uptake by the ocean is estimated with velocity fields derived from the GCM experiments. The sensitivity of the uptake to
different diffusion parameterizations and different surface forcing used in the GCM is investigated by conducting the three
GCM experiments; the diffusive processes are parameterized by horizontal and vertical eddy diffusion which is used in many
previous models (RUN1), parameterized by isopycnal diffusion (RUN2), and isopycnal diffusion and perpetual winter forcing
for surface temperature and salinity (RUN3). Realistic features for water masses and CFCs can be simulated by the isopycnal
diffusion models. The horizontal and vertical diffusion model fails to simulate the salinity minimum and realistic penetration
of CFCs into the ocean. The depth of the salinity minimum layer is better simulated under the winter forcing. The results
suggest that both isopycnal parameterization and winter forcing are crucial for the model water masses and CFCs simulations.
The oceanic uptake of anthropogenic CO2 in RUN3 is about 19.8 GtC in 1990, which is larger by about 10% than that in RUN1 with horizontal and vertical diffusive
parameterization. RUN3 well simulates the realistic water mass structure of the intermediate layer considered as a candidate
of oceanic sink for anthropogenic CO2. The results suggest that the previous models with horizontal and vertical diffusive parameterization may give the oceanic
uptake of anthropogenic CO2 underestimated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
52.
Y. Terada M. Ishida K. Makishima T. Imanari R. Fujimoto K. Matsuzaki H. Kaneda 《Monthly notices of the Royal Astronomical Society》2001,328(1):112-126
Extremely strong ionized Fe emission lines, with equivalent widths reaching ∼4000 eV, were discovered by ASCA from a few Galactic compact objects, including AX J2315−0592, RX J1802.1+1804 and AX J1842.8−0423. These objects are thought to be binary systems containing magnetized white dwarfs (WDs). A possible interpretation of the strong Fe K line is the line-photon collimation in the WD accretion column, as a result of resonance scattering of line photons. The collimation occurs when the accretion column has a flat shape, and the effect is augmented by the vertical velocity gradient, which reduces the resonant trapping of resonant photons along the magnetic field lines. This effect was quantitatively confirmed with Monte Carlo simulations. Furthermore, with ASCA observations of the polar V834 Centauri, this collimation effect was clearly detected as a rotational modulation of the equivalent width of the Fe K emission line. The extremely strong emission lines mentioned above can be explained consistently by our interpretation. Combining this effect with other X-ray information, the geometry and plasma parameters in the accretion column were determined. 相似文献
53.
54.
Yutaka?W.?WatanabeEmail author Hiroshi?Ishida Toshiya?Nakano Naoki?Nagai 《Journal of Oceanography》2005,61(6):1011-1016
Using time series of hydrographic data in the wintertime and summertime obtained along 137°E from 1971 to 2000, we found that
the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001∼0.004 μmol-PO4 l−1 yr−1 and 0.01∼0.04 μmol-NO3 l−1 yr−1 with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27∼0.48
mg-Chl m−2 yr−1 and 0.08∼0.47 g-C-NCP m−2 yr−1 with a clear oscillation of 20.8±0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation
Index (PDO) with a time lag of 2 years (R = 0.89 ± 0.02). Considering the recent significant decrease of O2 over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water
mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over
the western North Pacific. 相似文献
55.
We simulated two models of classical Cepheids with the same effective temperature and luminosity but different masses. Neither model has significant resonance among linear nonadiabatic periods of the fundamental, the first overtone, and the second overtone radial modes. The higher mass model found to approach to the second overtone-only state. The lower mass model shows a complicated three-mode interaction and none of the amplitudes of three modes is negligible. The relation of the higher mass model to the shortest period Cepheid HR 7308, and that of the lower mass model to the double-mode Cepheids are discussed. It appears that three-mode nonresonant coupling should be considered to explain the behaviours of both models. 相似文献
56.
T. Ishida 《Astrophysics and Space Science》1990,168(2):243-252
Amplitude equations, that are used in the investigation of stellar pulsations, for the three-mode nonresonant coupling case are inferred from that of the two-mode nonresonant coupling case. Characteristics of the fixed points of the amplitude equations are studied. Chaotic behaviour is expected when the amplitude equations consist of more than two modes. 相似文献
57.
T. Ishida 《Astrophysics and Space Science》1990,167(1):173-176
A criterion for the occurrence of double-mode pulsations is derived from linear adiabatic coupling coefficients The criterion indicates that double-mode pulsations of classical Cepheids occur at a shorter period range than the observed one, and that the evolutionary mass models are preferable for the double-mode pulsations. 相似文献
58.
mille E.O. Ishida Ribamar R.R. Reis Alan V. Toribio Ioav Waga 《Astroparticle Physics》2008,28(6):547-552
Cosmic acceleration is investigated through a kink-like expression for the deceleration parameter (q). The new parametrization depends on the initial (qi) and final (qf) values of q, on the redshift of the transition from deceleration to acceleration (zt) and the width of such transition (τ). We show that although supernovae (SN) observations (Gold182 and SNLS data samples) indicate, at high confidence, that a transition occurred in the past (zt > 0) they do not, by themselves, impose strong constraints on the maximum value of zt. However, when we combine SN with the measurements of the ratio between the comoving distance to the last scattering surface and the SDSS + 2dfGRS BAO distance scale (Sk/Dv) we obtain, at 95.4% confidence level, and for (Sk/Dv+Gold182), and and for (Sk/Dv+SNLS), assuming qi = 0.5 and qf = −1. We also analyze the general case, qf (−∞, 0) finding the constraints that the combined tests (Sk/Dv+SNLS) impose on the present value of the deceleration parameter (q0). 相似文献
59.
Two categories of earthquake precursors,physical and tectonic,and their roles in intermediate-term earthquake prediction 总被引:1,自引:0,他引:1
Katsuhiko Ishibashi 《Pure and Applied Geophysics》1988,126(2-4):687-700
I suggest that earthquake precursors can be divided into two major categories, physical and tectonic. I define physical precursor to be a direct or indirect indication of initiation or progression of an irreversible rupture-generating physical process within the preparation zone of a forthcoming earthquake. Tectonic precursor is defined as a manifestation of tectonic movement which takes place outside the preparation zone of an impending earthquake as a link in a chain of particular local tectonism in each individual area preceding the earthquake.Most intermediate-term, short-term and immediate precursors of various disciplines within the source regions of main shocks are considered physical ones. Some precursory crustal deformations around the source regions are, however, possibly tectonic precursors, because they may be caused by episodic plate motions or resultant block movements in the neighboring regions of the fault segments that will break. A possible example of this phenomena is the anomalous crustal uplift in the Izu Peninsula, Japan, before the 1978 Izu-Oshima earthquake ofM
s
6.8. Some precursory changes in seismicity patterns in wide areas surrounding source regions also seem to be tectonic precursors, because they were probably caused by the particular tectonic setting of each region. A typical example is a so-called doughnut pattern before the 1923 Kanto, Japan, earthquake ofM
s
8.2.Although most studies on earthquake precursors so far seem to regard implicitly all precursory phenomena observed as physical ones, the two categories should be distinguished carefully when statistical analysis or physical modeling is carried out based on reported precursory phenomena. In active plate boundary zones, where a practical strategy for earthquake prediction may well be different from that in intraplate regions, tectonic precursors can be powerful additional tools for intermediate-term earthquake prediction. 相似文献
60.
Overview of the MITI Nankai Trough Wells: A Milestone in the Evaluation of Methane Hydrate Resources 总被引:4,自引:0,他引:4
Yoshihiro Tsuji Hisashi Ishida Masaru Nakamizu Ryo Matsumoto Satoshi Shimizu 《Resource Geology》2004,54(1):3-10
Abstract. Bottom-simulating reflectors suggestive of the presence of methane hydrates are widely distributed below the ocean floor around Japan. In late 1999, drilling of the MITI Nankai Trough wells was conducted to explore this potential methane hydrate resource and a Tertiary conventional structure. The wells are located in the Northwest Pacific Ocean off Central Japan at a water depth of 945 m. A total of six wells were drilled, including the main well, two pilot wells, and three post survey wells at intervals of 10–100 m. All wells except the first confirmed the occurrence of hydrates based on logging-while-drilling, wire-line logging and/or coring using a pressure and temperature coring system in addition to conventional methods. Based on the various well profiles, four methane hydrate-bearing sand-rich intervals in turbidite fan deposits were recognized. Methane hydrates fill the pore spaces in these deposits, reaching saturation of up to 80 % in some layers. The methane hydrate-bearing turbiditic sand layers are less than 1 m thick, with a total thickness of 12–14 m. The bottom depth of high hydrate concentration correlates well with the depth of the bottom-simulating reflector. Based on these exploration results, the Japanese government inaugurated a 16-year methane hydrate exploitation program in 2001. 相似文献