巻号一覧
45 巻, 1 号
選択された号の論文の9件中1～9を表示しています
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H. Nakajima, H. Fukunishi, T. Ono, F. J. Rich1993 年 45 巻 1 号 p. 1-22
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーThe particle data of the DMSP-F6 and -F7 satellites show the presence of suprathermal electron bursts in the diffuse aurora region. These bursts are characterized by intense (∼108-109 (cm2sr sec)-1), low energy (∼100-500 eV), and localized (∼20-30 km at satellite altitude h ≅ 830 km) electron precipitation. Simultaneous magnetic field data from the DMSP-F7 satellite show that these bursts are often, but not always, accompanied with intense (few μAm-2), small-scale (only few tens of km at satellite altitude) upward field-aligned currents. The bursts are observed from 19 h to 11 h MLT through midnight during the maximum to recovery phase of substorm. These bursts are less likely to be observed during geomagnetic storms than during times of isolated substorms. These results suggest that suprathermal electron bursts are generated by localized heating of ionospheric electrons which flow out from the ionosphere toward the magnetosphere during substorm.抄録全体を表示PDF形式でダウンロード (81037K) -
I. M. Podgorny, S. Sasaki, N. Kawashima1993 年 45 巻 1 号 p. 23-27
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーThe contributions of critical velocity ionization and ions production at charge exchange are compared in space experiment. The results of Space Shuttle experiment SEPAC are discussed. Observed phenomena are explained by electron heating during the development of a lower hybrid instability in beam-beam plasma interactions.抄録全体を表示PDF形式でダウンロード (92782K) -
Iwao Iwamoto1993 年 45 巻 1 号 p. 29-40
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーThe mass spectrometric observations by the ISS-b satellite at an altitude of 1100 km during a period of solar maximum (1978-1981) have enabled to investigate the diurnal behavior of the equatorial He+ trough. Case studies using the individual pass plots show that the depth of the trough tends to be maximum around midnight. A statistical analysis has revealed that at the crest latitude He+ density maximizes at midnight while at the equator it becomes minimum at night. From these characteristics, it is concluded that the latitudinal change of the reservoir effect of the plasmasphere is the primary mechanism for the formation of the equatorial He+ trough. The equatorial anomaly in the NmF2 distributions, which were observed simultaneously by ISS-b, has apparent similarity to the equatorial He+ trough, however, the statistical analysis has shown that the diurnal behavior of NmF2 at its crest is definitely different from that of He+. This difference suggests the adequacy of the interpretation of the He+ trough in terms of the reservoir effect rather than the fountain effect due to E x B drift, which has been known to be responsible for the equatorial anomaly in NmF2. The results of ISS-b on NmF2 are consistent with this fountain effect. It is also suggested that E x B drift and/or the neutral winds modify the distributions of NmF2 and He+ to the extent that they exhibit similar latitudinal profiles.抄録全体を表示PDF形式でダウンロード (122350K) -
Takehiko Aso1993 年 45 巻 1 号 p. 41-63
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーAtmospheric solar tides observed in the middle atmosphere reveal various temporal and spatial variability, and snap-shot observations sometimes deviate from “average” tidal features. To evaluate transient behavior of this global-scale wave, time evolution of solar atmospheric tide has been investigated by means of time-dependent numerical modelling. A spectral method is applied to the primitive equation system, in which horizontal momentum equations, thermodynamic equation and lower boundary condition for the geopotential height are solved by the appropriate time integration scheme, with the continuity and hydrostatic equations solved downward and upward, respectively, in the altitude direction. Boundary conditions assume non-slip hypothesis below and diffusion-dominated spongy layer above. Time evolution of (2, 2) mode for the forcing with rise time of 2 days exhibits set-up time of 20 days or more, and vertical group propagation in the lower altitude region is shown to be comparable to theoretical value of about 0.6 m/sec. For (1, -2) mode, set-up time is short, and oscillation of complex amplitude with period of about 1.2 day is detected which might be due to beats with excited 5∼7-day period normal mode wave. Propagating (1, 1) mode shows smaller vertical group velocity for the rise-up of tidal structure. Semidiurnal tide excited non-linearly by the diurnal thermotidal forcing shows horizontal velocity component of some 10 m/sec at around 90 km which might affect the linear description of semidiurnal tide. These and other findings are informative to delineate tidal variability quantitatively.抄録全体を表示PDF形式でダウンロード (172409K) -
Yasuharu Sano1993 年 45 巻 1 号 p. 65-77
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーA new scaling law for the planetary magnetism was developed on the assumption that the Lorentz force balances the Coriolis force in the planetary core. In deriving the scaling law we decomposed the vector fields into the toroidal and the poloidal components, and dealt with them separately. From the scaling law, not only we can predict the dipole moments of the planets, but also can we estimate the toroidal magnetic field intensity in the planetary core; the result implies a typical toroidal magnetic field intensity of 100 [G], and the toroidal and the poloidal velocity fields respectively of the orders of 1 x 10-5 [ms-1] and 4 x 10-7 [ms-1] in the Earth's core. Since the present study is based on an αω-dynamo model, the resultant scaling law depends on the efficiency of the α-effect. If we adopt the dependence of the form α ∝ Ω (with Ω the angular velocity of the planet's self-rotation), the magnetic dipole moment M of a planet scales as M ∝ (characteristic length)7/2(mean density)1/2(angular velocity). The predictions agree well with the observations except Venus and Mars.抄録全体を表示PDF形式でダウンロード (203962K) -
Masayuki Seki, Keisuke Ito1993 年 45 巻 1 号 p. 79-88
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーIt is generally considered that the polarity reversal intervals have an exponential distribution. We have examined the distribution using all reversal data back to about 165 m.y. ago, and found that this distribution follows a power-law rather than an exponential. Power laws are common in critical phenomena, and therefore we propose that the geodynamo is marginally stable and that the geomagnetic polarity reversal is a kind of critical phenomenon. We present a simple model in which turbulent eddies in the outer core are assumed to behave as magnetic spins. By numerical simulation, we found that intervals of polarity reversals in the model follow a power-law at a critical state. When the energy dissipation accompanying polarity reversals is taken into account, the model self-organizes to the critical state.抄録全体を表示PDF形式でダウンロード (23K) -
Masaki Takahashi, Yoshio Watanabe1993 年 45 巻 1 号 p. 89-101
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーPaleomagnetism of the Miocene igneous rocks in the Uchiyama area, central Japan, have been determined in an effort to clarify the rotation of the Kanto Mountains located on the east wing of the sharp bent structure of the pre-Neogene basement rocks (Kanto Syntaxis). A mean tilt-corrected paleomagnetic direction of the Yaekubo Formation (D = -145.3°, I = -51.2°, α95 = 4.4°) shows eastward deflected declination indicating the clockwise rotation of the east wing of the Kanto Syntaxis. The radiometric ages of the andesite lava in the Yaekubo Formation (11.9 ± 0.9 Ma, 12.2 ± 0.3 Ma and 12.4 ± 0.4 Ma) signify that the about 35° clockwise rotation of the east wing of the Kanto Syntaxis occurred since 12 Ma. Along with the previous paleomagnetic studies in the Kanto Mountains and in its adjacent area into consideration, we can conclude that the lateral bending of the Kanto Syntaxis was formed in the Middle to Late Miocene.抄録全体を表示PDF形式でダウンロード (35207K) -
Chihiro Kaito, Yoshio Saito, Kazushi Ohtsuka, Tsuyoshi Watanabe1993 年 45 巻 1 号 p. 103-107
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーPericlase fine grains have been formed by evaporating magnesium in mixture gases of Ar (80%) and O2 (20%) at 13 kPa by heating at 1000°C. Forsterite fine grains have been produced by flushing SiO powders into the flame during MgO grain formation. Periclase and metal magnesium grains were also produced in atmosphere.抄録全体を表示PDF形式でダウンロード (15594K) -
J. Y. Liu, Y. N. Huang, F. T. Berkey1993 年 45 巻 1 号 p. 109-114
発行日: 1993/01/20
公開日: 2007/04/03
ジャーナル フリーPrevious theoretical models showed that, in the middle geomagnetic latitudes the oscillations in the Doppler frequency shift lag and lead the H component of ULF pulsations field on the ground, owing to the advection and compression mechanisms by 90°, respectively. On March 24, 1991, measurements obtained from a CW-HF Doppler sounding system and a fluxgate magnetometer show phase differences of 15°-77° between the Doppler frequency shift oscillations and the H component of ULF pulsations field at ground level, which indicates that the Doppler velocity arises from predominant changes due to the compression mechanism.抄録全体を表示PDF形式でダウンロード (15509K)
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