Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
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Volume 43, Issue 12
Displaying 1-4 of 4 articles from this issue
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  • Method to Subtract an Effect of the Geocorona EUV Radiation from the Low Energy Particle (LEP) Data by the Akebono (EXOS-D) Satellite
    T. HIGUCHI
    1991 Volume 43 Issue 12 Pages 957-978
    Published: 1991
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.43.957
    JOURNAL FREE ACCESS
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    It was found that the LEP data was sometimes contaminated with unexpectedly larger noise mainly due to the geocorona EUV radiation. Its noise level is so high that we are obliged to subtract the background noise in ground processing when we intend to analyze such LEP data. We therefore propose an efficient and useful procedure for eliminating this background noise, which is highly implemented so as to reduce the computing time. This method is based on a Bayesian smoothness prior approach with a state space modeling. The estimated background noise component is easily realized as a fixed-interval smoothed value by using the recursive Kalman filter and smoother algorithm. In addition, since we use an objective criterion ABIC to choose the best model for the LEP data with the background noise, then the background noise component is automatically and objectively (not ad-hoc) subtracted according to the characteristics of noise such as the signal-to-noise ratio, its intensity, and various nonstationarity. A detail description of the whole procedure based on a Bayesian approach can be shown.
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  • Electromagnetic Response Function for the Period of 27 Day in the Chinese Region
    P. F. CHEN, P. C. W. FUNS
    1991 Volume 43 Issue 12 Pages 979-987
    Published: 1991
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.43.979
    JOURNAL FREE ACCESS
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    Using the “Sompi” spectral analysis method, the daily mean values for 14 geomagnetic observatories in the Chinese region have been analysed for determining the magnitudes and phases of the P10 response corresponding to the period of 27d. The contour maps for the apparent depth h and the conductivity σ of the perfect substitude conductor were then plotted for this period. The results indicate that the lateral changes of σ and h are not very large in the central and northern Chinese region, where the average value of h is around 950km and the average value of σ is around 1.0S/m. These values are basically in agreement with those obtained by SCHULTZ and LARSEN (1987) for the neighbouring observatories of China—Irkutsk, Memambetsu, Kakioka and Kanoya. In the southern Chinese observatories we have found lower values of σ and larger values of h. It is not clear whether this characteristic feature in the southern Chinese region is due to the influence of the highly conducting ocean or the equatorial electrojet current or the poor signal to noise ratio in the data of Z magnetic component.
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  • Paleomagnetism of Volcanic Rocks from Rarotonga and Rurutu, the Cook-Austral Island Chain
    Hayao MORINAGA, Satoru YAMAGUCHI, Masayuki HYODO, Hiroo INOKUCHI, Nobu ...
    1991 Volume 43 Issue 12 Pages 989-1006
    Published: 1991
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.43.989
    JOURNAL FREE ACCESS
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    Rarotonga (21°15′S, 159°45′W) and Rurutu (22°30′S, 151°20′W) are volcanic islands included in the Cook-Austral island chain. Volcanic rock samples were collected at seven and ten sites in Rarotonga and Rurutu, respectively. The mean direction of magnetization for Rarotonga is 173.8° in declination and 46.2° in inclination (k=72.0 and α95=7.9°) and is more reliable than that from a previous work. The mean direction for three young rock sites in Rurutu is 218.2° in declination and 39.5° in inclination (k=49.3 and α95=17.7°) which for five old rock sites is 188.1° in declination and 51.4° in inclination (k=254.2 and α95=4.8°).
    These paleomagnetic results are in accordance with the total intensity anomaly pattern on each island, calculated using observed values of the geomagnetic field total intensity. The implication for the formation of these two islands inferred from the present results is consistent with that inferred from K-Ar ages and 87Sr/86Sr ratios by previous works. The formation of Rarotonga and Rurutu may be explained well by the concept of a “hot line” in a previous work rather than by the well-known “fixed hot spot” hypothesis.
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  • International Geomagnetic Reference Field, 1991 Revision
    INTERNATIONAL ASSOCIATION OF GEOMAGNETISM AND AERO
    1991 Volume 43 Issue 12 Pages 1007-1012
    Published: 1991
    Released on J-STAGE: September 14, 2010
    DOIhttps://doi.org/10.5636/jgg.43.1007
    JOURNAL FREE ACCESS
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