Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
48 巻, 8 号
選択された号の論文の8件中1~8を表示しています
  • K. Kudela, D. Venkatesan, R. Langer
    1996 年 48 巻 8 号 p. 1017-1024
    発行日: 1996/08/20
    公開日: 2007/05/25
    ジャーナル フリー
    Variability of the power spectra of cosmic ray temporal profiles in the frequency interval 1.2 × 10-5 Hz (f1) to 1.7 × 10-3 Hz (f2) in the period of two years shows that the integrals of power spectrum density over the interval f1 to 2.8 × 10-4 Hz (P1) are significantly correlated at two neutron monitors differing inacceptance cones and cut-off rigidities. At high frequency region, J>2.8 × 10-4Hz, the integrals P2 are correlated much less. P1 are weakly correlated with the cosmic ray intensity itself. Cross correlation between the time series P1 and the daily averages of geomagnetic indices (Kp, Dst and Ap) is asymmetric, with the maximum shifted to positive time lag. This indicates the stronger relation of the daily averaged geomagnetic indices measured for given day with the P1 obtained a day before, than with the P1 at the same day. The shift is not obtained if cosmic ray intensity, instead of P1, is cross-correlated with geomagnetic indices.
  • S. O. Ifedili
    1996 年 48 巻 8 号 p. 1025-1031
    発行日: 1996/08/20
    公開日: 2007/05/25
    ジャーナル フリー
    The Forbush decrease in the cosmic-ray albedo neutron flux has been measured by a neutron detector on board the OGO-6 satellite. For the events of June 7-10 and September 27-30, 1969, the Forbush decrease totalled 4.6 and 6% in amplitude respectively for the Mt. Washington neutron monitor (Pc=1.24 GV) while the respective depressions on the OGO-6 neutron rates in the polar region (Pc < 0.3 GV) were 5 and 9%. The depression in the OGO-6 neutron rates was larger at higher geomagnetic latitudes than at lower latitudes. These results indicate that Forbush decrease has greater effect on lower-energy charged particles, and that the phenomenon is reflected in the production of neutrons in the earth's atmosphere. However, it appears that the integrated effects of Forbush decreases on cosmic-ray albedo neutrons do not significantly decrease the CRAND source of charged particles in the radiation belt. For vertical cutoff rigidities Pc, < 1 GV, the total percent decrease in the OGO-6 neutron rates (≤10 MeV) during the Forbush decreases, 1969 June 7-10, September 27-30, and November 21-December 6 can be represented by -mPc+k. Values of m and k are each constant for the particular Forbush decrease but increase with increasing Mt. Washington neutron monitor monthly average rates, an indication of a flattening of the rigidity dependence of Forbush decrease towards maximum solar modulation.
  • Pierre Langlois, Léonard Bolduc, Michel C. Chouteau
    1996 年 48 巻 8 号 p. 1033-1041
    発行日: 1996/08/20
    公開日: 2007/05/25
    ジャーナル フリー
    Solar flares emit charged particles and ionizing rays into space which, if they interact with the magnetosphere, induce magnetic and electric fields in the earth. After the loss of power of the entire Hydro-Québec network following a geomagnetic storm in March 1989, a number of companies realized the importance of GICs (geomagnetically induced currents) in power transmission. As part of the effort to understand the causes and effects of GICs, a research team at Hydro-Québec measured the electric and magnetic fields for a period of 500 days at a rate of 8640 points per day and found that the electric fields occur with a probability inversely proportional to their amplitude according to a type x law.
  • G. G. Bowman
    1996 年 48 巻 8 号 p. 1043-1057
    発行日: 1996/08/20
    公開日: 2007/05/25
    ジャーナル フリー
    Days of maximum 10.7 cm solar flux associated with solar rotations have been used as controls to investigate, using superposed-epoch methods, spread-F occurrence levels over a range of latitudes from sub-auroral regions to equatorial-anomaly crest regions. For all latitude regions, 27-day periodicities, and other periodicities of lesser significance, were recorded in the spread-F plots, with minima in the oscillations located near the central positions. For these oscillations spread-F occurrence levels changed by 5 percent in sub-auroral regions, about 15 percent in mid-latitude regions and 10 percent in low-latitude regions. It can be seen that, as the sun rotates, solar-activity changes have a significant influence on spread-F occurrence. With some complications, generally the spread-F minima were delayed after the solar-flux maxima by a few days. These and other experimental results suggest an explanation in terms of an hypothesis which considers the so-called 27-day variation of the upper-atmosphere neutral-particle density (neutral density) associated with the solar-rotations. The proposal is that it is the control by the neutral density of the medium-scale travelling ionosphere disturbance wave amplitudes which determines whether or not spread-F is observed on ionograms.
  • T. Iyemori, T. Kamei, Y. Tanaka, M. Takeda, T. Hashimoto, T. Araki, T. ...
    1996 年 48 巻 8 号 p. 1059-1070
    発行日: 1996/08/20
    公開日: 2007/05/25
    ジャーナル フリー
    Impulsive co-seismic geomagnetic variations were observed at two stations nearly 100 km apart from the source region of the 1995 Hyogoken-Nanbu earthquake (M= 7.2). The maximum amplitude at the main shock was 0.6∼1.0 nT and the duration was 20∼30 seconds. These variations seem to have commenced at the origin time and before the arrival of the seismic waves to the observation site of 17 seconds later. A superposed epoch analysis for the aftershocks also reveals similar geomagnetic variations though the amplitude of them is one order of magnitude smaller than that of the main shock. A crustal dynamo mechanism is discussed as a possible cause of such co-seismic geomagnetic variations.
  • Satoshi Furwara, Hiroaki Tou
    1996 年 48 巻 8 号 p. 1071-1101
    発行日: 1996/08/20
    公開日: 2007/05/25
    ジャーナル フリー
    Repeated measurements of the Earth's time varying magnetic field have been made across Japan by the Geographical Survey Institute. Such measurements are known as a first order geomagnetic survey. There are 105 geomagnetic stations located uniformly across the whole of Japan. Since 1987, triaxial fluxgate magnetometers have been used to obtain one-minute data at almost all stations. From the geomagnetic data, transfer functions were determined for each station. Traditional vertical field transfer functions of wide period range (from 4 min to 128 min) were obtained, making use of the interstation method. Additionally, we calculated transfer functions for the horizontal field. The distribution of the transfer functions can be used to form a reference map of geomagnetic induction in Japan. Moreover, the distribution of the horizontal transfer functions in Japan has been examined for the first time. After eliminating the effect of the sea water using thin-sheet models, large regional anomalies are found to remain. These anomalies are diagnostic of the resistivity structure and show patterns of current channeling in Japan.
  • Kazuo Saito, Masaki Takahashi, Naoto Onozuka
    1996 年 48 巻 8 号 p. 1103-1109
    発行日: 1996/08/20
    公開日: 2007/05/25
    ジャーナル フリー
    Thermochronological investigations have been carried out on the Chichibu Quartz Diorite in order to elucidate the detailed timing of intrusion and its cooling history. The Chichibu Quartz Diorite is a small pluton (6 × 3 km) situated in the central part of the Kanto Mountains, Japan. Newly obtained K-Ar ages from 6 biotites, ranging from 5.6 to 6.8 Ma, and from 2 hornblendes, ranging from 6.0 to 6.1 Ma, strongly suggest that the Chichibu Quartz Diorite experienced a considerably rapid cooling. Combining with previously reported paleomagnetic results, we can conclude that the body formed and subsequently cooled around Chron C3A of Cande and Kent's (1995) geomagnetic polarity time scale.
  • 1996 年 48 巻 8 号 p. 1111
    発行日: 1996年
    公開日: 2011/08/11
    ジャーナル フリー
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