Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
Search
Advanced search
OR
Browse
Search
Volume 44, Issue 10
Displaying 1-7 of 7 articles from this issue
Show all abstracts
    • |<
    • <
    • 1
    • >
    • >|
  • Response of the Sq and Equatorial Electrojet Variations to the North-South Asymmetry in Geomagnetic Activity
    G. K. RANGARAJAN, Ajay DHAR
    1992 Volume 44 Issue 10 Pages 899-908
    Published: 1992
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.44.899
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    The nature of the diurnal variation of the ionospheric component of the equatorial electrojet and planetary Sq field is studied using the horizontal intensity data of a suitable triad of stations in the Indian zone separately for conditions of enhanced geomagnetic activity in the northern and southern hemispheres. It is shown that the influence of the North-South asymmetry is manifested in distinct fashions in the diurnal patterns of Sq and jet. Disturbance dynamo caused by even moderate geomagnetic activity appears to alter the shape and structure of the equatorial electrojet and the planetary Sq current systems. Conspicuous absence of the difference when the asymmetry in geomagnetic activity vanishes confirms the perceptible influence of the N-S asymmetry on the ionospheric current system at low and equatorial latitudes.
    View full abstract
    Download PDF (904K)
  • A Simplified Theory of the Neutral Wind System
    Ken-ichi MAEDA
    1992 Volume 44 Issue 10 Pages 909-917
    Published: 1992
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.44.909
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    In the theories of atmospheric tide and dynamo, a singularity appears in the equation of the neutral velocity owing to an effect of Coriolis force. To avoid the difficulty a certain mathematical technique has been devised and Hough function was born.
    The present paper shows that the difficulty is removed by applying the principle of continuity of the horizontal velocity. It is found that the wind system thus obtained is very close to the important modes such as (1, -2) obtained from the usual tidal and dynamo theories. Comparative study is made on the construction of driving force and velocity in the usual and the present theories.
    View full abstract
    Download PDF (498K)
  • Magnetic Shielding by a Spherical Shell Having a Hole (2)
    Tsuneji RIKITAKE
    1992 Volume 44 Issue 10 Pages 919-929
    Published: 1992
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.44.919
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    Magnetic shielding by a spherical shell having a hole is studied. Unlike RIKITAKE (1990), in which the magnetic field externally applied to a spherical shell is parallel to the line that connects the center of the shell to that of the hole, the field is directed perpendicular to the said line.
    Much of the evaluation of magnetic potential and field is similar to that of RIKITAKE (1990). It turns out that the smaller the hole size, the higher the shielding power. It is interesting and important, however, that the shielding power decreases only by a few tens of percent when the hole aperture radius is 30° or smaller. A fairly large defect of the shell may be allowed without losing much shielding power. The conclusions are much the same as those in RIKITAKE (1990).
    View full abstract
    Download PDF (753K)
  • Magnetic Field Reversal Resulting from a Dynamo Process in a Spherical Shell
    Y. HONKURA, T. IIJIMA, M. MATSUSHIMA
    1992 Volume 44 Issue 10 Pages 931-941
    Published: 1992
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.44.931
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    The magnetic field is one of the intrinsic properties of the Earth, originating in a magnetohydrodynamic (MHD) process in the liquid outer core. It also exhibits a variety of features of secular variation; most typically, reversals of the polarity of the axial dipole term and westward drifts of the non-zonal terms. Here we report on the results of our simulations of an MHD dynamo process in a rotating spherical shell and demonstrate that the above two typical features of the Earth's magnetic field can be understood quite naturally without any specific conditions. We also examine how the virtual geomagnetic pole (VGP) moves, in our MHD dynamo model, during transitional stages from one polarity to the other, and show that some features of the transitional behaviour derived from the paleomagnetic data can be seen in our dynamo model as well.
    View full abstract
    Download PDF (1016K)
  • Separation of Paleomagnetic Secular Variation Components
    A Method and Its Application to a Sedimentary Record from Japan
    Chizu ITOTA, Masayuki HYODO, Katsumi YASKAWA
    1992 Volume 44 Issue 10 Pages 943-957
    Published: 1992
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.44.943
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    A new method is introduced to analyze paleosecular variations of the earth's magnetic field direction. The method consists of the following four steps. First, a time series of a pair of declination and inclination is transformed into two components defined in ADF reference frame. Second, characteristic periods are estimated with a spectral analysis. Third, the secular variation components of the periods are separated through band-pass filters. Finally, the motion of field vectors is investigated with respect to its curvature on a polar projection for each secular variation component. The present method has been applied to the sedimentary secular variation record from central and southwest Japan for the last 12000 years. The results indicate two main periodic motions of field vectors with the periods of about 700 and 2350 years. The 2350 years component is dominated by smooth clockwise motions. This suggests that the westward drifting field has persisted almost steadily for the last 12000 years. However, the breakup of the clockwise motion took place between 4500 and 8100 years B. P., which may have been generated by an accidental temporary standing field. The 700 years component is characterized by the thin elliptic motion whose major axes remained almost constant during more than 1750 years long and rotational sense changed frequently. This elliptic motion may have been caused by intensity changes in standing fields added with week drifting fields.
    View full abstract
    Download PDF (1451K)
  • Carboniferous-Triassic Paleomagnetism of South Korea
    Kwang Ho KIM, Jong Deok LEE, Min Ok CHOI
    1992 Volume 44 Issue 10 Pages 959-978
    Published: 1992
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.44.959
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    Middle Carboniferous to Early Triassic paleomagnetic directions from Northeast Okchon Fold Belt of South Korea have been obtained and used to calculate the paleopoles of South Korea. Many samples collected are strongly overprinted by the Brunhes normal magnetic field, but thermal demagnetization has been successful in isolating ancient, dualpolarity characteristic directions of magnetization, with results passing reversal and fold tests. An Early Triassic direction (D=76.8°/I=37.2°, α95=8.9°, k=29.3, Nchr=18), a Late Permian direction (D=258.0°/I=12.2°, α95=16.4°, k=14.4, Nchr=7), and a Middle Carboniferous direction (D=100.5°/I=-22.5°, α95=13.0°, k=17, Nchr=18) have been obtained from the Northeast Okchon Fold Belt of South Korea.
    Southern Korea and South China Block (SCB) yield Jurassic and younger paleopoles that are to first approximation similar, but on the other hand Carboniferous-Triassic Apparent Polar Wander Path is different from that of SCB. Inclinations and declinations calculated from these two paths for the Korean reference site are significantly different in the Carboniferous-Triassic. It is, therefore, insisted that the southern part of Korean Peninsula and SCB were different tectonic masses before the Jurassic.
    View full abstract
    Download PDF (1719K)
  • Self-Reversal of Thermo-Remanent Magnetization in Pyroclastics from the 1991 Eruption of Mt. Pinatubo, Philippines
    M. OZIMA, M. FUNAKI, N. HAMADA, S. ARAMAKI, T. FUJII
    1992 Volume 44 Issue 10 Pages 979-984
    Published: 1992
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.44.979
    JOURNAL FREE ACCESS
    Show abstractHide abstract
    We studied magnetic properties of the pyroclastics of the 1991 eruption of Mt. Pinatubo. At one locality of the pyroclastic flows, the directions of natural remanent magnetizations (NRMs) of dacite pumice fragments are dispersed, indicating that these fragments settled after their temperature reached their Curie points. At another locality, almost all dacite pumice fragments show reversed NRMs, indicating that these settled before their temperature reached the Curie point thereby acquiring a self-reversed thermo-remanent magnetization in the ambient geomagnetic field. Almost all the dacite pumice samples from both localities acquied self-reversed TRMs in the laboratory. Detailed examination revealed that these dacite pumice samples in the pyroclastic flows of the 1991 eruption of Mt. Pinatubo have characteristics of the Haruna-type self-reversal of thermo-remanent magnetization.
    View full abstract
    Download PDF (526K)
    • |<
    • <
    • 1
    • >
    • >|
feedback
 Top