巻号一覧
48 巻, 12 号
選択された号の論文の8件中1～8を表示しています
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V. I. Shishov, M. Tokumaru1996 年 48 巻 12 号 p. 1461-1480
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーThe theory of the scintillation temporal power spectrum and two frequency co-spectrum for radio waves propagating through the near-Sun interplanetary plasma is considered. The relative contributions of the regular motion, turbulent velocity fluctuations and turbulent wave propagation are discussed. The comparison of theory and the known observational data indicates that for distances r < 10R, velocity fluctuations due to large scale Alfvénic waves are most important. For distances 10R < r < 40R, the temporal spectrum is determined by the solar wind motion and slow magnetosonic wave propagation.抄録全体を表示PDF形式でダウンロード (2797K) -
R. G. Rastogi, H. Crandra, M. E. James1996 年 48 巻 12 号 p. 1481-1488
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーThe disintegration of vortex type of ionospheric Sq current system in the northern hemisphere along the Asian longitudes during the local winter months (December solstices) is manifested by the abnormally low daily variation of the eastward component of the geomagnetic field (Y) at any of the stations. Such a weakening of the Sq(Y) field during local winter months is not observed at east African or Australian stations.抄録全体を表示PDF形式でダウンロード (21415K) -
Yih-Hwa Chen, Yen-Hsyang Chu, Chao-Han Liu1996 年 48 巻 12 号 p. 1489-1497
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーWith employing 52 MHz Chung-Li VHF radar, the ionospheric irregularities embedded in sporadic E layer in equatorial anomaly crest zone are observed. It shows that in general the echoes of sporadic E irregularities in association with plume-like structures are occurred in the height range from 99 km to 122 km and centered at around 108 km, quite consistent with the observations made by local HF ionosonde. Spectrally analyzing the radar returns indicates that the low-velocity type 1 (or type 3) and type 2 radar spectra are both observed and may appear simultaneously in the same Doppler spectrum. Their characteristics are estimated and discussed in the text. Differing from those obtained by using VHF radars situated in equatorial and auroral zone, the Doppler velocities of type 1 (or type 3) radar spectra observed here are generally within 95∼115 ms-1, fairly smaller than the former ones. The typical Doppler velocity and spectral width for type 2 radar spectra are within -150-160 ms-1 and 16-30 Hz, respectively. The average drift velocity of 3-meter irregularities deduced from type 2 spectra is also presented. It displays that the drift is toward the radar at the lower height, while away above approximately 104 km. Moreover, below the altitude of around 108 km the drift velocity varies substantially with height at the gradient of about 10 ms-1/km. Above that height, the drift velocity changes slightly with height. The plausible process corresponding to these two distinct behaviors of height variation of drift velocity are also discussed in this article.抄録全体を表示PDF形式でダウンロード (2172K) -
Yasuyuki Iwase1996 年 48 巻 12 号 p. 1499-1514
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーWe study the numerical simulations of 3-D inifinite Prandtl number convection with temperature-dependent viscosity in a spherical shell. Control volume method coupled with SIMPLE algorithm is used to solve the basic equations. Both constant and temperature-dependent viscosity cases are studied under the condition that the ratio of the inner to the outer shell radius is 0.55, which is appropriate for mantle convection of the Earth, with only basal heating. For the case of constant viscosity, when the Rayleigh number (Ra) is less than 105, steady state solutions (both cubic and tetrahedral types) are obtained. However, for Ra = 106, we find only a time-dependent solution. For the temperature-dependent viscosity case, we assume that the viscosity changes with temperature exponentially and we can successfully obtain solutions with the viscosity variation up to 10000. For the viscosity contrast of 1000 times and the surface Rayleigh number of Ra0 = 5 × 103, we get the flow patterns which consist of the sheet-like downwelling and small upwellings.抄録全体を表示PDF形式でダウンロード (32709K) -
Tsuneji Rikitake1996 年 48 巻 12 号 p. 1515-1521
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーA method for numerically solving Laplace's equation in three-dimensional spherical space is developed relying on relaxation technique. It is demonstrated that upward continuation of magnetic potential for the 1990 IGRF non-dipole field expressed by spherical harmonics of low degree and order can be successfully made on a personal computer.抄録全体を表示PDF形式でダウンロード (945K) -
Luiz Muniz Barreto1996 年 48 巻 12 号 p. 1523-1530
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーThe determination of geographic azimuths is an essential step in field magnetic surveys. In spite of the relatively low precision required for declination values, it is strongly recommended that those true azimuths should be measured with an error in the order of 0.1' to avoid contamination of desired magnetic values. The applicability and ease of use, as well the deficiencies of the various methods of azimuth determination must be considered in the light of the different field work conditions encountered during repeat station surveys. In general, four classes of methods could be considered: geodetic, astronomical, use of a gyro-theodolite and use of a GPS system. The strengths and weakness of each of these methods are discussed and a comparison between them is made. Notwithstanding a possible worldwide interest of this subject, a special emphasis is given to magnetic repeat station work in developing countries. As a conclusion, we could say that the most suitable method for azimuth determination at a magnetic repeat station strongly depends on regional conditions. For developing countries (latitude range between 30°N and 30°S), mainly for Latin American countries, the gyro-theodolite method proves to be very effective at the present time.抄録全体を表示PDF形式でダウンロード (1983K) -
M. E. Evans, L. Jiang1996 年 48 巻 12 号 p. 1531-1540
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーA survey of the main magnetomineralogical characteristics of 92 archeomagnetic samples from 37 sites in Greece, Italy, North Africa, and China is presented. Coercive force spectra suggest that magnetite and/or titano-magnetite dominates both natural and laboratory remanences (NRM, ARM and IRM). This is confirmed by thermal demagnetization, which establishes the overwhelming role played by these minerals. Magnetic granulometry techniques indicate that no particular domain state predominates. Some samples are dominated by very small particles near the single-domain/superparamagnetic boundary, some by pseudo-single domain particles, and others by what we interpret as mixtures.抄録全体を表示PDF形式でダウンロード (1407K) -
Hideo Tsunakawa, Makoto Okada, Nobuaki Niitsuma1996 年 48 巻 12 号 p. 1541-1552
発行日: 1996/12/20
公開日: 2007/05/25
ジャーナル フリーThe method of deconvolution of post-depositional DRM (detrital remanent magnetization) is applied to the paleomagnetic directions of continuous sedimentary sections from two sites in the Boso Peninsula, Japan. These sections have different accumulation rates and cover a time span of about 1000 years that includes the Matuyama-Brunhes reversal. Since the remanences are thought to be of the post-depositional DRM origin, a new deconvolution method with an exponential fixing function is applied. The deconvolution restores relative intensities of three components in the original fields from the remanence directions. As a result, the half-fixing depth is estimated to be 21 cm and the three-dimensional plot of the relative intensity is given. In the diagram of X and Z components, the polarity change in the geocentric axial dipole field with some additional field is recognized during the main reversal, while there seems to be no correlation between X and Y. After the deconvolution, the VGP path during the main reversal does not show longitudinal confinement, but does show longitudinal drift near the equator.抄録全体を表示PDF形式でダウンロード (28425K)
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