Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
43 巻 , 4 号
選択された号の論文の6件中1~6を表示しています
  • S. O. IFEDILI
    1991 年 43 巻 4 号 p. 255-266
    発行日: 1991年
    公開日: 2010/09/14
    ジャーナル フリー
    The nature of atmospheric neutrons as well as their contributions to the earth's radiation belts are discussed. Our estimates of the trapped proton fluxes from atmospheric neutrons indicate that GRAND, cosmic ray albedo neutron decay, is the major source of protons (E>30MeV) in the radiation belts for L≤1.8. More trapped proton differential energy measurements at L>1.8 are required in order to test the CRAND theory at L>1.8.
    The CRAND as well as the solar proton albedo neutron decay (SPAND) source is found too weak to supply the large low energy (≤10MeV) inner zone proton intensities.
    However, the inner zone proton fluxes from our cross-L diffusion calculations are in reasonable agreement with the observed fluxes at energies ≤30MeV. Diffusion inward from the solar wind appears to be the major source of the low energy inner zone protons.
  • Masashi HAYAKAWA
    1991 年 43 巻 4 号 p. 267-276
    発行日: 1991年
    公開日: 2010/09/14
    ジャーナル フリー
    The morphological characteristics of whistler-triggered VLF emissions including diurnal, seasonal variations, Kp dependence, latitudinal distribution and spectral shape, were investigated based on the VLF data obtained at Moshiri (L=1.6) in Japan during a ten year span (1976 to 1985). The following results emerged; (1) There is no clear tendency for whistler-triggered emissions to occur at a particular local time, (2) an equinoctial maximum in occurrence probability is recognized, (3) the occurrence probability increases with increasing Kp in the range from 3 to 7, (4) the occurrence L shell is localized in two regions; one is L=2.1 to 3.4 (the electron slot region) and the other is just around L=1.6 (the inner radiation belt), and (5) a whistler-triggered emission is characterized by an initial component quasi-constant frequency and a subsequent large frequency drift with df/dt=10-20kHz/s. These characteristics are satisfactorily interpreted in terms of the gyroresonance interaction between lightning-generated whistlers and energetic electrons, with reference to previous results on lightning-induced particle precipitation.
  • Hidefumi TANAKA, Hideo TSUNAKAWA, Hiromitsu YAMAGISHI, Gaku KIMURA
    1991 年 43 巻 4 号 p. 277-294
    発行日: 1991年
    公開日: 2010/09/14
    ジャーナル フリー
    A paleomagnetic study was made for Miocene-Pliocene volcanic and sedimentary rocks from the Shakotan Peninsula, West Hokkaido, Japan (43.2°N, 140.5°E). Out of 20 rock units sampled, 18 sites were successful to reveal stable remanence but three sites were rejected because of their anomalous directions. Although most of the sites showed in situ directions coinciding with the direction of the present earth's field (PEF), we did not adopt the usual rejection criterion; the NRM in which the in situ direction is close to the PEF should be automatically rejected. Our opinion is that as long as the original stable remanence is detected there is no need to, rather better not to, reject such NRM directions. To support this idea we compared decay curves of remanence in AF demagnetization among NRM, IRM, and ARM. The total mean paleomagnetic direction (I=55.6°, D=14.7°, α95=9.5°) is slightly eastward and gives a paleomagnetic pole (77.9°N, 249.5°E, α95=12.1°) which might suggest a clockwise block rotation of the Shakotan Peninsula. However, we concluded that this pole for middle Miocene to Pliocene is not significantly apart from the present geographical pole on 95% confidence level. On the same confidence level, the pole position agrees with some of the contemporary poles from Northeast Japan implying the same block of West Hokkaido and Northeast Japan. This pole position also indicates that the Shakotan Peninsula did not suffered much tectonic deformation from the collision of East Hokkaido and the Kuril arc to the middle part of Hokkaido which is considered to have occurred after the late Miocene (KIMURA and TAMAKI, 1985). The northerly paleodirection revealed by the lowest sedimentary rock (-15Ma) might be an indication of the timing of rotation of Northeast Japan earlier than Southwest Japan.
  • K. PEC, J. PECOVÁ, Z. MARTINEC
    1991 年 43 巻 4 号 p. 295-306
    発行日: 1991年
    公開日: 2010/09/14
    ジャーナル フリー
    A numerical approach for solving forward electromagnetic induction problem has been suggested. It takes into consideration the terms involving the conductivity gradient. Some numerical solutions are presented for conductivity models containing narrow bellshaped zones in which the electrical conductivity varies very strongly. These zones of anomalous conductivity variations at depths of 100 or 600km influences the shape of response functions in the period range from 1 to 100 days.
  • A. N. GOLOVIN, V. P. GOLOVKOV, N. M. ROTANOVA
    1991 年 43 巻 4 号 p. 307-317
    発行日: 1991年
    公開日: 2010/09/14
    ジャーナル フリー
    The separation of the field of secular variations into the drifting and non-drifting parts by methods worked out by Yukutake and James-Nevanlinna is discussed. The reliability of these techniques is studied on the basis of the international geomagnetic reference field (IGRF) data. The conclusion is drawn about the statistical insignificance of the results of the separation. Using multipole analysis, the authors reject the hypothesis that the multipole grows (decays) and undergoes a rigid rotation around an axis without any structural changes.
  • H. NEVANLINNA, L. HÄKKINEN
    1991 年 43 巻 4 号 p. 319-321
    発行日: 1991年
    公開日: 2010/09/14
    ジャーナル フリー
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