巻号一覧
48 巻, 10 号
選択された号の論文の6件中1～6を表示しています
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Yohei Yamauchi, Masayoshi Kojima, Munetoshi Tokumaru, Hiroaki Misawa, ...1996 年 48 巻 10 号 p. 1201-1217
発行日: 1996/10/20
公開日: 2007/05/25
ジャーナル フリーWe study the properties of micro-turbulence in the solar wind using interplanetary scintillation (IPS) observations made with the single dish antenna operating at 2.3 GHz and 8.5 GHz. Our IPS observations were made during September-October in 1992 and 1993 and covered a radial distance range of 5-76 solar radii (Es). We apply the spectral-fitting method to obtain properties of solar wind turbulence, such as axial ratio of anisotropy, inner scale of dissipation length, power-law spectral index, and solar wind velocity. We also examine the velocity dependence of the turbulence near the sun, and find the following results. (1) Both low-speed and high-speed solar-wind flows show acceleration at the distance range of 10-30 Rs, which is consistent with previous works. (2) The radial dependence of anisotropy and spectral index show no significant difference between the low-speed and high-speed solar wind. (3) Only the inner scale length shows a dependence on flow speed: the inner scale in the high-speed wind is 1.4 ± 0.3 times larger than that in the low-speed wind.抄録全体を表示PDF形式でダウンロード (46353K) -
T. Iyemori, M. Takeda, A. Saito, T. Araki, T. Hashimoto, Y. Tanaka1996 年 48 巻 10 号 p. 1219-1232
発行日: 1996/10/20
公開日: 2007/05/25
ジャーナル フリーThe solar and IMF effects were statistically detected in mid-latitude (L = 1.25) ionospheric electric field data obtained by the MU radar. It was found that the IMF-Bx component (sector polarity) and the solar radio flux (SRF) correlates with the north-south component of the electric field on the night-side. For more positive (sunward) Bx, or for greater SRF, the electric field is more southward/downward. However, strong mutual correlation between the IMF-Bx and the SRF is found in the period analyzed (1987-1993), suggesting that the night-side correlation between electric fields and IMF-Bx comes from the effect of the solar activity rather than the direct influence of the IMF-Bx. In fact it was also found from the data for almost two solar cycles that the IMF-Bx (or By) dependence of the ionospheric foF2 is very similar with the solar activity (sunspot number) dependence of it. This suggests that the mutual correlation between the solar activity and the IMF-Bx, (or By) causes the apparent correlation of the foF2 with the IMF-Bx which has been reported as a sector polarity effect. On the other hand, the direct effects of the IMF-Bx (or By) on the electric fields were also detected by taking the correlations between the time differentials of them and the results are consistent with the known IMF effects on the Sq focus location. The differentials of the IMF-Bz have significant correlation with the electric fields in limited local time zones and the sense of electric field is consistent with the penetration of the dawn-to-dusk electric field in the magnetosphere indicating the imperfect shielding by the plasmasphere.抄録全体を表示PDF形式でダウンロード (2653K) -
E. Apostolov, D. Altadill, L. Alberca1996 年 48 巻 10 号 p. 1233-1239
発行日: 1996/10/20
公開日: 2007/05/25
ジャーナル フリーIt is found that quasi-2-day oscillations persist in the geomagnetic activity indices an, as and am and time variations of the oscillation characteristics are examined. The 3-hourly indices for 1964-1986 are used for analysis. The main results are: 1) the oscillation persists almost continuously, 2) there are not significant hemispheric differences of the oscillation period and amplitude, 3) the dominant period is 48 hours, 4) there is expressed a semi-annual variation of the oscillation period with minimum in solstices and maximum in equinoxes, 5) the oscillation amplitude is modulated by semi-annual and long-term geomagnetic variations. A possible way for inducing such oscillations in the time variations of geomagnetic activity indices is proposed.抄録全体を表示PDF形式でダウンロード (18933K) -
Yu. I. Galperin, M. Hayakawa1996 年 48 巻 10 号 p. 1241-1263
発行日: 1996/10/20
公開日: 2007/05/25
ジャーナル フリーA new analysis is described for the published data from the MASSA active experiments held in 1981-1983 in the USSR. These tests were aimed to simulate earthquake effects in the magnetosphere and ionosphere using surface chemical explosions. Measurements in the magnetosphere above the explosions were made from the AUREOL-3 satellite (Galperin et al., 1985a, 1985b). ELF/VLF noises were excited within an altitude range from 410 km to ≈ 2000 km along the Explosion plasma Flux Tube (EFT), based on the E-region above the explosion point (L ≈ 1.5). During the MASSA-1 experiment, at L ≈ 1.3, before the EFT crossing, 5 minutes after the explosion at L = 1.5, a strong upward moving MHD-impulse was registered with a sharp front. The front was accompanied by excited ion sound waves. Indirect arguments are presented for the origin of the impulse within the EFT, its bouncing and accompanied cross-L drift to, and then trapping at L = 1.3. The effects observed suggest the existence of a natural MHD-impulse generator and/or its power amplifier located in the middle atmosphere not higher than 70 km. It generates/amplifies the electromagnetic response in the magnetosphere and ionosphere. It is suggested that the form of electric discharges in the middle atmosphere known as “red sprites” or “blue jets” can serve the role of the natural generator/power amplifier for the effects in the ionosphere and magnetosphere observed in the MASSA experiments. If real, it can be speculated, that similar “amplification” effects through atmospheric electrical discharges could play a role in the generation of some earthquake precursor effects observed in the magnetosphere and ionosphere.抄録全体を表示PDF形式でダウンロード (5300K) -
Wataru Kanda, Hisashi Utada, Masaaki Mishina, Norihiko Sumitomo1996 年 48 巻 10 号 p. 1265-1280
発行日: 1996/10/20
公開日: 2007/05/25
ジャーナル フリーIn November 1993, a time domain electro-magnetic (TDEM) experiment was carried out in the northern part of Miyagi Prefecture, northeastern Japan. The observation area is of high seismic activity, where a magnitude 6.5 earthquake occurred in 1962 and its aftershocks can be still observed. The purpose of this observation is to investigate how this seismic activity is related to the electric resistivity structure. We aimed to investigate the resistivity structure down to a depth of 10 km or so, where most recent earthquakes took place. For the field experiment, an approximately 2 km long grounded wire was used as an artificial source. Receivers were located at a distance of several kilometers from the transmitter, where three components of the magnetic field were measured using a high sensitivity fluxgate magnetometer. High quality transient data were obtained from measurements made at 10 sites for 4 days, with total data length of about 27 hours. After proper techniques of the data analysis were applied, the resistivity structure was estimated by comparing not only the vertical but also the horizontal magnetic components with the synthetic master curve for one dimensional (1-D) resistivity model. Preliminary result shows that a highly conducting crustal layer exists below the north-eastern part of the survey area where micro seismicity is rather shallower. On the other hand, we could not find a crustal conductor within the range of field penetration depth in the southwestern part, where seismicity is deeper.抄録全体を表示PDF形式でダウンロード (41543K) -
Nagendra P. Singh, T. Lal1996 年 48 巻 10 号 p. 1281-1294
発行日: 1996/10/20
公開日: 2007/05/25
ジャーナル フリーThe problem of calculating the electromagnetic (em) field response of a horizontal magnetic dipole placed over a multi layer earth model with one of the layers having linear variation of conductivity with depth is formulated. Analytical solutions are obtained for the three layer earth model having linear variation of conductivity in the intermediate transition layer, for the case of quasi-static approximation. Computations are performed for the absolute-amplitude ratio, i.e. the ratio of the absolute amplitude of the field component over a multi-layer model and the corresponding component over a homogeneous half space possessing the conductivity of the top layer. The effects of transition layer thickness and conductivity contrast between the top and bottom layers are investigated by computing these ratios as a function of numerical distance. The results depict characteristic dependence of the em response on conductivity inhomogeneity.抄録全体を表示PDF形式でダウンロード (23923K)
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