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Volume 32 (1980)
- Issue 12 Pages 721-
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Volume 16 (1964)
- Issue 4 Pages 221-
- Issue 3 Pages 165-
- Issue 2 Pages 75-
- Issue 1 Pages 1-
Volume 16, Issue 3
Displaying 1-6 of 6 articles from this issue
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Self-reversal and Recovery Phenomena of Remanent MagnetizationMituko OZIMA, Minoru OZIMA, Syun-iti AKIMOTO1964 Volume 16 Issue 3 Pages 165-177
Published: December 01, 1964
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSBehaviours of remanent magnetization of magnetite are studied for low temperature range from room temperature to liquid nitrogen temperature (-190°C). The remanent magnetization produced at room temperature on magnetite decreases sharply when magnetite is cooled from room temperature to liquid nitrogen temperature, and recovers a certain percentage of the intensity of the original remanent magnetization when heated to the room temperature (recovery phenomenon), or decreases further in the heating. In some of single crystal magnetites, however, the remanent magnetization was found to reverse its direction at about -145°C in the cooling in non-magnetic space.
In order to explain the anomalous behaviours of a remanent magnetization at low temperatures, it is assumed that the heterogenity in the stress distribution or in other physical conditions in a grain would result in a heterogeneous distribution of isotropic points (temperatures at which crystal anisotropy energy becomes minimum) within a grain. On the basis of these assumptions, it is shown that the regions with different isotropic points then would interact magnetostatically with each other resulting in the self-reversal or the recovery phenomenon.
Cobalt was found to show the similar recovery and reversal phenomena of a remanent magnetization when it is cooled from 400°C to room temperature in nonmagnetic space. Since cobalt has an isotropic point at about 250°C, the self-reversal and the recovery phenomena may be explained in the same way as in magnetite.View full abstractDownload PDF (1469K) -
T. YUKUTAKE, M. SAWADA, T. YABU1964 Volume 16 Issue 3 Pages 178-182
Published: December 01, 1964
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSRemanent magnetization of ash-fall tuffs, which were collected from successive layers at a certain locality of Oshima Volcano was measured. It was ascertained that the remanent magnetism of ash-fall tuffs was so stable that it can possibly be used for archaeomagnetic purpose. Declination and inclination obtained from ash-fall tuffs agree with those from lavas and so they can well be used for filling up the gap of the secular variation curve whicn has been obtained only from the archaeomagnetic studies of lavas.View full abstractDownload PDF (509K) -
T. YUKUTAKE, K. NAKAMURA, K. HORAI1964 Volume 16 Issue 3 Pages 183-193
Published: December 01, 1964
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSThe validity of making use of subaerial ash-fall tuffs in archaeomagnetism, was examined by measuring samples collected from the same ash-fall tuff bed at different parts of Izu-Oshima Island. Magnetization of these tuffs agrees with each other quite well. Moreover, it has turned out that the magnetization of ash-full tuffs is so stable and strong that even a small fluctuation of the magnetic field due to the local anomaly at the time of deposition, may be detected.
All the results so far obtained by archaeomagnetic study on lavas and pyroclastics of Oshima Volcano are summarized.View full abstractDownload PDF (1229K) -
Minoru OZIMA, Hazimu KINOSITA1964 Volume 16 Issue 3 Pages 194-200
Published: December 01, 1964
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSThe saturation magnetic anisotropy of andesite in a fault zone is measured. It is found that anisotropy is more remarkable for samples closer to a fault and the origin of the anisotropy is essentially due to the shape alignment of magnetic grains in rocks. On the basis of these experimental results it is suggested that the fault movement is responsible for the observed shape alignment of grains in the rocks. Finally, from the measurement of the magnetic anisotropy in three mutually perpendicular disks cut from the rock samples, the direction of the fault movement is estimated.View full abstractDownload PDF (656K) -
Pre-SC Field Intensity Increase of WWV 20Mc/s Received at Hiraiso, JapanTadanori ONDOH, Koji OBU, Yugoro TAKENOSHITA1964 Volume 16 Issue 3 Pages 201-209
Published: December 01, 1964
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSStorm-time variation of WWV 20Mc/s field intensity at Hiraiso is examined for about 50 geomagnetic storms during August 1957-February 1959. An abnormal increase of field intensity of WWV 20Mc/s appears from about 12 hours before a geomagnetic storm sudden commencement to a few hours after it. It is found that the storm-time variation of f0F2 deviation from the monthly median also shows pre-SC augmentations for the corresponding storm-time interval at Winnipeg and Fairbanks, which are located at approximate apexes of the Washington-Hiraiso 3 hops path. This close relation between these pre-SC phenomena suggests that the pre-SC intensity increase of HF polar path may be useful for the radio warning especially for periods of the solar minimum activity.View full abstractDownload PDF (1014K) -
Takesi NAGATA, T. IIJIMA1964 Volume 16 Issue 3 Pages 210-220
Published: December 01, 1964
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSThe average patterns of equivalent ionospheric current system of polar magnetic storms (Dp-field) for both northern and southern polar regions are constructed by analyzing exactly simultaneous data in both polar regions during the IGY period. Those data of magnetic storms are classified into two groups; i. e., severe storm for which Kp=7.2 and moderate storm for which Kp=4.3.
In both cases, the Dp patterns for the northern and southern polar regions are almost exactly symmetric with each other with respect to the geomagnetic coordinates, suggesting that the geomagnetic conjugacy well holds between the two polar regions.
Several remarks are made on mechanism of causation of the Dp field. It is emphasized, in particular, that the larger part of polar cap currents of the Dp field may be attributable to an enhancement of the Sqp field by a stronger solar wind.View full abstractDownload PDF (1296K)
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