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Volume 46, Issue 5
Displaying 1-6 of 6 articles from this issue
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A. Prigancová, M. Bieleková, Ya. I. Feldstein1994 Volume 46 Issue 5 Pages 341-361
Published: May 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSUsing a large sample of storms of different intensity the ring current magnetic field development is followed in terms of varying interplanetary conditions. It is shown that although the storm depression field is associated with energy input into the magnetosphere, the sustained IEF intensity <-5 mV/m as a condition for the occurrence of intense storms appears not to be of general validity. Quantification of the magnetic storm development indicates the role of the actual state of the magnetosphere in the development of its response on interplanetary medium forcing. Ring current energization is considered for some storm models represented by pairs of energy injection rate and time decay parameter. A number of models are juxtaposed quantitatively. The adequacy of modeling of storm profiles and the significance of decay parameter in the magnetic storm development is discussed from the viewpoint of consistency of energy injection rate and energy decay rate and also with regard to an adequate distribution of dissipated energy within the ring current region and auroral ionosphere.View full abstractDownload PDF (58920K) -
Ken-ichi Kato, Natsuo Sato, Yutaka Tonegawa1994 Volume 46 Issue 5 Pages 363-372
Published: May 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSWe have attempted to estimate geomagnetic conjugate points using Pc5 geomagnetic pulsation data. The Pc5 pulsation data were obtained simultaneously at three coordinated stations in Iceland and at three stations in Antarctica, including Syowa Station, for the months of March and May in 1988. In this analysis, it was principally assumed that Pc5 pulsations have a form of odd mode standing oscillations of the geomagnetic field line with linear phase shifts among the stations in the horizontal plane. Conjugate points were calculated uniquely. The statistical result showed that conjugate points of Syowa Station estimated from the Pc5 events were concentrated around the conjugate points in Iceland calculated from the magnetic field model of Tsyganenko (1987) within the range of 66°-68° in latitude, and 70°-76° in longitude, i.e., less than 1/5 wave length.View full abstractDownload PDF (24985K) -
G. K. Rangarajan1994 Volume 46 Issue 5 Pages 373-380
Published: May 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSQuasi-bidaily Variation (BDV) in the geomagnetic field due to equatorial electrojet and planetary Sq currents is clearly detected in the Indian equatorial zone. The quasi-stationary signal is stronger in EEJ compared to SQ. Larger amplitude of the BDV in EEJ is confined only to late summer in the northern hemisphere indicative of its clear association with the planetary wave in the mesosphere below. A noticeable change in the BDV amplitude is seen following counter electrojet events. However, no concrete evidence is seen for the anticipated association between the movement of Sq focus caused by mesospheric winds and the BDV in EEJ or Sq.View full abstractDownload PDF (23569K) -
Jiro Segawa, Kin-ichiro Koizumi1994 Volume 46 Issue 5 Pages 381-391
Published: May 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSSince 1987 we have been working with the establishment of the sea floor observation stations in order to detect long-term geophysical changes. Study of the changes of geomagnetic field is one of the most important works to be carried out on the station. The sea floor observation station is a fixed and nonmagnetic platform installed firmly on the sea floor, which is easily accessible by manned submersibles. We have installed three such observation stations in the Sagami Bay which is close to Tokyo. The operation and observation were carried out with the aid of the Japanese Submersible SHINKAI 2000 every year. Measurements were made four times in the last four years. Duration of the measurement was from 1 hour to 25 hours depending on the conditions of the submersible. The equipment used to measure the geomagnetic total force is a proton magnetometer specially designed for the sea floor. The sensor is a toroidal coil dipped totally in Kerosene oil which is pressure-balanced by means of Beryllium-Copper bellows. The magnetometer is installed on the platform exactly in the same fashion every time. Transportation and installation are made by the submersible using manipulators. By comparing the data from the sea floor with those of the land geomagnetic stations, we confirmed the feasibility of detecting changes of geomagnetic total force on the sea floor.View full abstractDownload PDF (24681K) -
Jinqi Hao, Jianguo Zhou1994 Volume 46 Issue 5 Pages 393-402
Published: May 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSIn the present study, an experiment under uniaxial pressure with 126 samples of 26 rock types is carried out. The general nature of remanence changes with stress is far more complicated than estimated hitherto. The authors suggest that these changes can be distinguished into three types. In Type-I and -II effects, the changes of remanence with stress are. all regular, however the former is weakly irreversible and the latter is strongly irreversible when the stress is released. In Type-III effect, the remanence shows a very jumbly and irregular variation with stress. According to the comprehensive study on magnetism of these rocks, the appearance of the Type-III effect is relevant to dominant VRM in NRM and specific domain state of the magnetic minerals in the rocks. In this experiment it is also discovered that a sort of relatively high-frequency variation superimposes on the general change of remanence under pressure. It appears to be related with the closing of existed microcracks and opening of newly-developing microcracks. Above-mentioned three types of piezomagnetic effect seem corresponding to certain kinds of earthquake precursors, while some sorts of tremble-variation in magnetization could be distinguished from local magnetic field data. The results of this experiment imply that in order to search and understand complicated seismomagnetic effects, specific content and microscopic structure of medium in seismic regions should be noticed.View full abstractDownload PDF (23936K) -
Yasuo Ogawa, Makoto Uyeshima, Yoshimori Honkura, Hisashi Utada, Shiger ...1994 Volume 46 Issue 5 Pages 403-408
Published: May 20, 1994
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSA tensor audio-frequency (10, 000-1 Hz) magnetotelluric method was used to image the Kita-Izu fault system, a typical active strike-slip fault in Japan. Regional strike direction (N55°E) was first determined after decomposing tensor impedances; this direction is consistent with the strike of geomorphology and also with the strike of the fault. Local anisotropy and site gain were then corrected for each site. Finally, the impedances were inverted using two-dimensional modeling with a smoothness constraint. The model shows (1) that the fault corresponds to a discontinuity of the surface resistive volcanic cover and (2) that there is a significant conductive anomaly (∼ 1 Ωm) beneath the valley at 500 m depth from the surface, which may correspond to a fractured zone.View full abstractDownload PDF (14714K)
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