Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
Volume 29, Issue 2
Displaying 1-5 of 5 articles from this issue
  • Yutaka KONDO, Toshihiro OGAWA
    1977 Volume 29 Issue 2 Pages 65-80
    Published: 1977
    Released on J-STAGE: March 12, 2010
    JOURNAL FREE ACCESS
    The diurnal variations of odd nitrogen species (N, NO) in the thermosphere are modelled by solving the time-dependent, one-dimensional continuity equations with the diffusion transport which have been developed by OGAWA and SHIMAZAKI (1975). By comparing the calculated results with N and NO distributions which were determined in an airglow (NI 5, 200Å and NO gamma-bands) and mass spectrometric observations the following conclusions have emerged. (1) The quantum yield of N(2D) in the reactions energetically capable of producing the excited species should be larger than 0.5, and probably as large as 0.9. (2) The quenching of N(2D) by atomic oxygen is important at altitudes above 120km. In order to be consistent with the observation of NI 5, 200Å airglow, the quenching coefficient must be as large as 1×10-12cm3s-1. (3) The variability of NO density profiles obtained by various experimenters is largely interpreted to be due to the large diurnal variations of odd nitrogen expected from a large diurnal change in the thermospheric temperature which is also under the control of solar activities.
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  • Marianne MARESCHAL, Jerry L. KISABETH
    1977 Volume 29 Issue 2 Pages 81-104
    Published: 1977
    Released on J-STAGE: March 12, 2010
    JOURNAL FREE ACCESS
    A major problem encountered when modeling external current systems from ground-based magnetic observations is the evaluation of the earth's induction effects. Though it is quite difficult to represent accurately the effects of induced currents flowing inside the earth, they can be approximated relatively easily under certain circumstances (i. e. when global rather than local electrical properties of the earth are concerned). For this purpose, two general classes of earth models can be used, i. e. (1) the models which reduce the earth to a superconductor (either at the surface or at some depth) and (2) the models in which the earth is represented by a body of finite conductivity (either uniform or layered). The performances of these two types of earth models are tested with respect to substorm modeling from mid-latitude data (i. e. when neither the curvature of the earth nor the three-dimensional nature of the substorm current system can be neglected). The conclusions are almost identical to those obtained previously with high latitude data (i. e. when the induction problem can be reduced to the study of a flat electrojet flowing over a flat earth). They indicate that for most problems of substorm modeling from ground-based magnetic observations, it is sufficient to treat the earth as a superconductor (“perfect” conductor).
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  • S. O. OGUNADE, H. W. DOSSO
    1977 Volume 29 Issue 2 Pages 105-121
    Published: 1977
    Released on J-STAGE: March 12, 2010
    JOURNAL FREE ACCESS
    D'YAXONOV'S (1959) method for a sphere embedded in a uniform conducting half-space for an overhead vertical magnetic dipole has been extended to the case of a sphere embedded in the lower layer of a two layer conducting half space. The fields are evaluated at the interface of the two layer conductor. The numerical results obtained for a range of geophysical parameters have possible applications in the interpretation of ocean floor electric and magnetic field measurements.
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  • Leroy R. ALLDREDGE
    1977 Volume 29 Issue 2 Pages 123-135
    Published: 1977
    Released on J-STAGE: March 12, 2010
    JOURNAL FREE ACCESS
    Harmonic analyses have been made of the geomagnetic horizontal component (H) and the vertical component (Z) from several observatories. These analyses indicate variations of tens of nanoteslas in the period range 13 to 30 years. The largest variation occurred for periods of approximately 25 years. For the pass band 13 to 30 years, several cases were found in which a group of neighboring observatories displayed similar variations. It is quite clear that the origin of these signals must be found in the core of the earth rather than outside the earth. The variations can not be explained by the westward drift of a core dynamo with a detailed fine structure. Hydromagnetic waves in the core offer a better explanation.
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  • D. R. K. RAO, B. R. ARORA
    1977 Volume 29 Issue 2 Pages 137-142
    Published: 1977
    Released on J-STAGE: March 12, 2010
    JOURNAL FREE ACCESS
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