Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
42 巻, 5 号
選択された号の論文の6件中1~6を表示しています
  • Takehiko ASO, Takeshi HASHIMOTO, Minoru ABE, Takayuki ONO, Masaki EJIR ...
    1990 年 42 巻 5 号 p. 579-595
    発行日: 1990年
    公開日: 2010/09/14
    ジャーナル フリー
    A method of analysis is investigated for the monochromatic aurora stereo TV observations at Antarctica. First, a camera model is obtained by using calibration data for the background stars. Second, an inverse problem is solved which reconstructs threedimensional luminosity structures of aurora photoemission from two-dimensional projection of auroral images. The method assumes prescribed spatial distributions of luminosity, parameters of which are to be determined by the nonlinear least squares method. A series of numerical tests indicates that stereo data give plausible estimation of the model parameters, but in some cases, the method is jeopardized due to unfavorable geometrical conditions. A preliminary analysis of the stereoscopic observation for the stable aurora arc is carried out, and the presumed structure of luminosity at 557.7[nm] wavelength is inferred.
  • J. S. KIM, G. S. N. MURTY, S. OKANO
    1990 年 42 巻 5 号 p. 597-606
    発行日: 1990年
    公開日: 2010/09/14
    ジャーナル フリー
    A large geomagnetic storm commenced at 00:00 UT in conjunction with a southward turning of the IMF on September 18, 1979. Ground-based measurements of the thermospheric temperatures and the meridional winds were made with a Fabry-Perot interferometer from Albany, New York. A meridian scanning multicolor photometer recorded a weak SAR-arc emission which reached a peak intensity of only 160R. Since the arc remained rather weak, the temperature enhancements within the arc were not noticeable and the meridional wind structure did not show any deviations. There was, however, a significant interruption in the development of the ring current between about 03:00 UT and 05:00 UT. But the growth phase re-emerged shortly after 05:00 UT, resulting in major changes in the auroral dynamics. The neutral temperatures showed general enhancements of 100K to 150K, consistent with the storm time conditions. The mean temperature was about 1324±164K. The meridional winds were directed equatorward and they ranged between 30m/s and 370m/s. Both the temperature and wind speed, as expected, decreased during the first half of the night, and then they showed a rapid and dramatic increase as several substorms occurred in rapid succession and the electrojet moved equatorward for the period between 05:00 and 10:00 UT. The maximum wind speed occurred some 40 minutes earlier than the occurrence of the maximum temperature, indicating that the temperatures and meridional winds in the mid-latitude thermosphere respond to substorm intensification in a different way.
    Cross-correlation analysis showed that there is a strong correlation between the enhanced neutral temperature and a parameter (AE2/D), which represents a ratio between the energy input by the auroral electrojet activity and the distance between the point of observation and the location of the energy deposition. The correlation coefficient is nearly 0.84.
  • Two-Dimensional Case Studies
    N. OSHIMAN
    1990 年 42 巻 5 号 p. 607-619
    発行日: 1990年
    公開日: 2010/09/14
    ジャーナル フリー
    A general theory of piezomagnetism in a uniform medium leads to the conclusion that a 1-nT change in the geomagnetic total intensity represents a change of 1.8×10-5 in strain. Empirically, however, a much larger tectonomagnetic change ΔF in units of nT has been observed for a strain ε. The ΔF/ε ratio amounts to some 10-3 in actual cases in contrast to 0.6×10-4 as expected from the theory.
    It is the aim of this paper to understand the reason why such a discrepancy takes place on the basis of non-uniform distribution of magnetic layers in the crust. For that purpose, the tectonomagnetic effect arising from an infinitely long cylinder, which is embedded in a semi-infinite medium and is subjected to internal hydrostatic pressure, is estimated for a number of models which represent non-regular distributions of magnetic layers.
    It turns out that, unlike the uniform model, the magnetic field arising from stress-induced magnetization is enhanced at some portions on the earth's surface depending on magnetic layer configurations because of the lack of symmetry of magnetization.
    Since the earth's crust is magnetically complicated, it is not unreasonable to expect tectonomagnetic changes of an appreciable order in favourable cases.
  • Mounir TRIGUI, Alain TABBAGH
    1990 年 42 巻 5 号 p. 621-636
    発行日: 1990年
    公開日: 2010/09/14
    ジャーナル フリー
    Susceptibility measurements were undertaken over 32 samples of oceanic basalts in weak uniform alternative field, in order to determine the variations of both in-phase and quadrature susceptibilities with frequency in the range 1Hz-10kHz.
    Multidomain grain basalts exhibit variations clearly different from single domain and pseudo-single domain ones, but in most cases a decrease of the in-phase susceptibility with frequency is verified. Except for four samples the direct proportionality between quadrature susceptibility and the first derivative of the in-phase susceptibility with frequency logarithm is also experimentally observed.
  • Song XU, Ronald T. MERRILL
    1990 年 42 巻 5 号 p. 637-652
    発行日: 1990年
    公開日: 2010/09/14
    ジャーナル フリー
    Stable moments associated with pinned walls in a multidomain (MD) grain can be screened by regions in which walls are free to move. This screening problem is investigated by using a new approximation method that linearizes the demagnetizing field acting on individual domain walls in a grain. The approximation is shown to be usually excellent by comparing results obtained from it to more precise numerical solutions. In addition, the approximation enables one to carry out analytical calculations. Screening in a MD grain is generally very complex, and it was argued by MOON and MERRILL (1986a) that it might even lead to a self-reversal of a grain in some cases. However, it is shown in this paper that the particular domain state required for such a self-reversal will not likely ever be realized in practice. Moreover, it is found that the screening effect cannot explain the decrease of partial thermoremanent magnetization (pTRM) on cooling that is sometimes observed in MD magnetites; instead some other process such as a transdomain process is likely involved.
  • Natsuo SATO, Thorsteinn SAEMUNDSSON
    1990 年 42 巻 5 号 p. 653-662
    発行日: 1990年
    公開日: 2010/09/14
    ジャーナル フリー
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