Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
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Volume 42, Issue 10
Displaying 1-6 of 6 articles from this issue
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  • Two-Dimensional Auroral X-Ray Image Observation at a Balloon Altitude in the Northern Auroral Zone
    T. YAMAGAMI, H. MIYAOKA, A. NAKAMOTO, Y. HIRASIMA, S. OHTA, M. NAMIKI, ...
    1990 Volume 42 Issue 10 Pages 1175-1191
    Published: 1990
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.42.1175
    JOURNAL FREE ACCESS
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    A balloon observation of auroral X-rays has been carried out by using two types of X-ray imagers. The first is a new type of imager consisting of a two-dimensional 5×5 matrix array of Si(Li) semiconductor detectors whereas the other is a one-dimensional array of 8 NaI(Tl) scintillation detectors. Both are pinhole camera type imagers. The balloon carrying these imagers was launched from Abelver, Norway, on July 5, 1985, and flew westward over Iceland. Near the location of L=5.2 at the geomagnetic midnight during a geomagnetic substorm, temporal variations of auroral X-ray images were observed with 3-s time intervals by the Si(Li) imager. These images were confirmed simultaneously by the NaI(Tl) imager. A time sequence of the auroral X-ray images did not show a stable arc structure, but rather a localized small-scale structure with rapid time variation. The present observation suggests that localized intermittent precipitations of energetic electrons with energies of several tens keV occurred in the post-break-up phase of an auroral substorm. It is fully possible that localized energetic electron precipitations are due to the localized field-aligned electric field.
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  • Rocket Measurements of O2 Atmospheric (0-0) and OH Meinel Bands in the Night Airglow
    Motoharu TAKANO, Takashi WATANABE, Masatoshi NAKAMURA
    1990 Volume 42 Issue 10 Pages 1193-1208
    Published: 1990
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.42.1193
    JOURNAL FREE ACCESS
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    O2(0-0) atmospheric and OH Meinel bands in the night airglow have been simultaneously measured using multi-color rocket-borne photometers in midlatitude. Atomic oxygen densities have been deduced from O2 airglow intensity profiles and the direct and two-step excitation mechanisms for the O2 airglow have been examined. The obtained atomic oxygen densities agree with in-situ measurements. The altitude profiles of the observed OH(8-3), (7-3) and (6-2) bands are reproduced by calculation using calculated atomic oxygen density profiles. It is clearly demonstrated that time-to-time variations of the altitude profile of atomic oxygen is basically important for the change of the OH altitude profile. The quenching rate of OH by O has been estimated to be small, with a best-fitted value of 5.1×10-12cm3sec-1.
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  • A New Inversion Scheme for Two-Dimensional Magnetotelluric Modelling
    Guoze ZHAO, Guodong LIU
    1990 Volume 42 Issue 10 Pages 1209-1220
    Published: 1990
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.42.1209
    JOURNAL FREE ACCESS
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    Based on the idea of electromagnetic skin depth, a two-dimensional magnetotelluric inversion scheme has been proposed in which the structure is determined step by step from a shallower to a deeper part. The inversion process begins at the shortest available period and then proceeds to longer periods successively. Forward calculation in the iteration process is carried out by using finite element technique. Construction of a starting model and modification of the model parameters during the iteration are accomplished automatically. Thus not only the resistivity, but also the geometry parameters of all blocks in the model can be determined. The Marquardt method is used in the inversion process. The results of application of the inversion technique to theoretical models and real field data show that the iteration process is so stable that convergence can be reached rapidly, which leads to significant reduction of computer time.
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  • Magnetic Shielding by a Spherical Shell Having a Hole (1)
    Tsuneji RIKITAKE
    1990 Volume 42 Issue 10 Pages 1221-1235
    Published: 1990
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.42.1221
    JOURNAL FREE ACCESS
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    Magnetic shielding by a spherical shell having a hole is studied. Solving the differential equation satisfied by magnetic potential, distributions of the potential are obtained for various combinations of hole size, shell thickness and magnetic permeability. Relaxation technique is used for solving the problem numerically. The shell is placed in a uniform external field parallel to the direction connecting the hole center to that of the shell.
    As expected, 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.
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  • Universal Diurnal Variation of F2-Layer Critical Frequency
    V. V. KUZNETSOV, V. V. PLOTKIN, I. I. NESTEROVA, M. S. POZDEEVA
    1990 Volume 42 Issue 10 Pages 1237-1240
    Published: 1990
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.42.1237
    JOURNAL FREE ACCESS
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  • Iron-Nickel Ordered Grains Produced by the Reaction of Metallic Film and Ultrafine Metallic Grains
    Chihiro KAITO, Yoshio SAITO
    1990 Volume 42 Issue 10 Pages 1241-1247
    Published: 1990
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.42.1241
    JOURNAL FREE ACCESS
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