Numerical modelling of space and time variations of seismic activity before major earthquakes     

Takeshi Mikumo  Takashi Miyatake 《Geophysical Journal International》1983,74(2):559-583

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Empirical formula to relate the auroral electrojet intensity with interplanetary parameters     

Takashi Murayama  Takao Aoki  Hitoshi Nakai  Kazuyuki Hakamada 《Planetary and Space Science》1980,28(8):803-813

An empirical formula has been constructed using the results of correlative analyses to determine in what form the AL index, as a measure of the intensity of the westward auroral electrojet, depends on interplanetary parameters. The formula thus obtained shows that AL is mainly determined by B_sV² where B_s is the southward component of the IMF and V is the solar wind velocity, and is modulated in a characteristic way by the combined effect of the east-west component of the IMF and the tilt angle of the Earth's dipole axis toward the Sun-Earth line. In contrast, effects of the solar wind density and the IMF variability were found to be insignificant.Implications of the empirical formula are discussed mainly in relation to the problem of the location in the dayside magnetosphere of the region where the reconnection process to initiate the substorm takes place.  相似文献   

Vibration of a disordered chain: A model to investigate light absorption of amorphous grain     

Takashi Onaka  Yoshikazu Nakada  Fumio Kamijo 《Astrophysics and Space Science》1979,65(2):259-273

Vibration of a two-component disordered chain of 500 atoms is investigated. The mass ratio is 28:16. Squared frequency-spectra are obtained for several cases with different degrees of disorder. For a simple case eigenvectors are also calculated to show that there exists a local vibration mode at disorder. If there is an additional impurity atom in the chain, there appear localized vibration modes at the impurity atom above the optical branch and between the optical and the acoustical branches. Vibration of the chain with variable force constants, which are governed by a probability distribution, is studied as a model for a glassy substance.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space Medium held at the Lunar and lanetary Institute, Houston, 6–8 September, 1978.  相似文献   

Altitude variation of ultraviolet oxygen night airglow     

Takashi Onaka  Mineo Sawamura  Wataru Tanaka  Toshihiro Ogawa 《Astrophysics and Space Science》1985,114(2):387-393

Night airglow of oxygen 130.4 and 135.6 nm emissions was measured by a spectrophotometer aborad an S520 sounding rocket, launched at 19:50 JST (10:50 UT) on 14 February, 1982 from Kagoshima, Japan. The altitude variation of the emissions was obtained from 110 to 266 km at zenith angles of 35.5°±4°. The emission intensity around 260 km was about 160R and is roughly compatible with model calculations taking account of O⁺+e ^– radiative recombination as well as O⁺–O^– mutual neutralization. Some excess of about 50R, compared to the model calculation, was observed around 200 km. Possible explanations of the excess are: (i) remnant oxygen ions during the transition period from day to night and (ii) diffuse radiation from the background sky. Model calculations taking account of remnant oxygen ions were also performed by adding an excess electron density to the original density profile. However, it was found that an unreasonably large electron density is required around 200 km (5×10⁵ cm^–3) to produce the observed intensity. It is also probable that some contribution from the background sky is present in the observed intensity.  相似文献   

Solubility of sulfur in some magmas at 1 atmosphere     

Takashi Katsura  Shigeru Nagashima 《Geochimica et cosmochimica acta》1974,38(4):517-531

In order to understand the distribution of sulfur in igneous rooks, we determined the solubility of sulfur in volcanic rock melts (tholeiite basalt, hawaiite and rhyodacite from Hawaii) at various gas compositions and at 1250° and 1300°C and 1 atm total pressure. The solubility of sulfur in the melt passes through a minimum with change in oxygen partial pressure, if other factors are held constant. For the basaltic liquid at 1200°C, most sulfur in the melt is as dissolved sulfide (S^?2) at oxygen partial pressures below 10^?8 atm and as dissolved sulfate at oxygen partial pressures above 10^?8 atm. Based on the present solubility data, 5 per cent is inferred for volcanic gas at 1 atm total pressure in equilibrium with subaerially extruded Hawaiian tholeiite basalt (Pele's hair with 180 ppm S) at 1200°C and 10^?8 atm P_O2.  相似文献   

Effects of CO<Subscript>2</Subscript> on Marine Fish: Larvae and Adults     

Atsushi Ishimatsu  Takashi Kikkawa  Masahiro Hayashi  Kyoung-Seon Lee  Jun Kita 《Journal of Oceanography》2004,60(4):731-741

CO₂-enriched seawater was far more toxic to eggs and larvae of a marine fish, silver seabream, Pagrus major, than HCl-acidified seawater when tested at the same seawater pH. Data on the effects of acidified seawater can therefore not be used to estimate the toxicity of CO₂, as has been done in earlier studies. Ontogenetic changes in CO₂ tolerance of two marine bony fishes (Pag. major and Japanese sillago, Sillago japonica) showed a similar, characteristic pattern: the cleavage and juvenile stages were most susceptible, whereas the preflexion and flexion stages were much more tolerant to CO₂. Adult Japanese amberjack, Seriola quinqueradiata, and bastard halibut, Paralichthys olivaceus, died within 8 and 48 h, respectively, during exposure to seawater equilibrated with 5% CO₂. Only 20% of a cartilaginous fish, starspotted smooth-hound, Mustelus manazo, died at 7% CO₂ within 72 h. Arterial pH initially decreased but completely recovered within 1-24 h for Ser. quinqueradiata and Par. olivaceus at 1 and 3% CO₂, but the recovery was slower and complete only at 1% for M. manazo. During exposure to 5% CO₂, Par. olivaceus died after arterial pH had been completely restored. Exposure to 5% CO₂ rapidly depressed the cardiac output of Ser. quinqueradiata, while 1% CO₂ had no effect. Both levels of ambient CO₂ had no effect on blood O₂ levels. We tentatively conclude that cardiac failure is important in the mechanisms by which CO₂ kills fish. High CO₂ levels near injection points during CO₂ ocean sequestration are likely to have acute deleterious effects on both larvae and adults of marine fishes. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Radioactive disequilibrium of thorium series nuclides in surface waters of the Seto Inland Sea     

Takashi Okubo 《Journal of Oceanography》1982,38(1):1-7

Surface samples of sea water collected in the Seto Inland Sea were analyzed for²³²Th and²²⁸Th. The concentrations of²³²Th were generally less than 2 dpm/1,0001 and these values are probably an upper limit for the²³²Th concentration in surface waters of the Seto Inland Sea. The²²⁸Th concentrations ranged between 4.2 to 42.3 dpm/1,0001. Remarkable seasonal and temporal variations in²²⁸Th concentrations were found, in comparison with the minimal variations in²²⁸Ra concentrations reported previously. The activity ratios of²²⁸Th/²²⁸Ra were about 0.18 in the southern part of the Kii and the Bungo Channels, and decreased markedly from the open ocean toward the central region of the Seto Inland Sea. The average value of the²²⁸Th/²²⁸Ra ratio in the central region of the Seto Inland Sea was 0.032±0.020. This suggests that removal residence time of²²⁸Th can be estimated to be about 34±22 days in surface waters of the Seto Inland Sea.  相似文献   

A weakly non-gaussian model of wave height distribution for random wave train   总被引：2，自引：0，他引：2  

Nobuhito Mori  Takashi Yasuda 《Ocean Engineering》2002,29(10):1219-1231

The wave height distribution with Edgeworth’s form of a cumulative expansion of probability density function (PDF) of surface elevation are investigated. The results show that a non-Gaussian model of wave height distribution reasonably agrees with experimental data. It is discussed that the fourth order moment (kurtosis) of water surface elevation corresponds to the first order nonlinear correction of wave heights and is related with wave grouping.  相似文献   

Coastal polynyas off East Queen Maud Land observed from NOAA AVHRR data     

Takayuki Ishikawa  Jinro Ukita  Kay I. Ohshima  Masaaki Wakatsuchi  Takashi Yamanouchi  Nobuo Ono 《Journal of Oceanography》1996,52(3):389-398

Coastal polynyas off East Queen Maud Land in Antarctica are examined using NOAA AVHRR infrared data. From image analyses, two locations of coastal polynyas in this region are identified; one in Breid Bay and the other along the shelf break. The areal coverage of the Breid Bay polynya is significantly related to the strength of katabatic winds, which maintain their strength over the coastal sea due to land topography favoring for their confluence, thereby being capable of removing newly formed ice. Land fast ice in the eastern part of the bay also plays an additional role in the formation mechanism. It is also found that the areal coverage of coastal polynyas in this region fluctuate coherently. Moreover, these fluctuations correspond to the synoptic index, which measures the strength of the offshore wind, with their peaks closely associated with the areal peaks. These facts strongly suggest the influence of synoptic scale weather on the formation and maintenance of polynyas in this region.  相似文献   

Change in the microzooplankton community during decay of aHeterosigma akashiwo bloom   总被引：2，自引：0，他引：2  

Kamiyama  Takashi 《Journal of Oceanography》1995,51(3):279-287

The temporal change in the microzooplankton community during the decay of a bloom ofHeterosigma akashiwo was investigated over a 10-day period in June–July 1991 at a site in western Hiroshima Bay, the Seto Inland Sea, Japan. The density ofH. akashiwo was at the order of 10⁴ cells·ml^–1 during the first 5 days, and decreased drastically when vertical mixing occurred.Heterosigma akashiwo cells disappeared after the eighth day. When the density ofH. akashiwo decreased suddenly, the density of microzooplankton increased rapidly. The increase in microzooplankton density was due to non-tintinnid ciliates. The species diversity of tintinnids was significantly higher in 1 and 2-m layers during the post-bloom period than during the bloom period. One species of tintinnid,Codonellopsis nipponica, was the most abundant in the bottom layer during the bloom period but decreased in abundance during the decay of the bloom. Populations of two species of hyaline tintinnids,Eutintinnus tubulosus andHelicostomella longa, were at low levels during the bloom period, and then developed suddenly after the bloom disappeared. It was demonstrated that the abundance and species composition of the ciliate community change dramatically during the decay of theHeterosigma bloom.  相似文献