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Inversion of Paleomagnetic Data

Research Project

Project/Area Number 10440124
Research Category

Grant-in-Aid for Scientific Research (B)

Allocation TypeSingle-year Grants
Section一般
Research Field 固体地球物理学
Research InstitutionOkayama University (1999)
The University of Tokyo (1998)

Principal Investigator

KONO Masaru  Institute for Study of the Earth's Interior, Okayama University, Professor, 固体地球研究センター, 教授 (20011596)

Co-Investigator(Kenkyū-buntansha) TANAKA Hidefumi  Faculty of Education, Kochi University, Associate Professor, 教育学部, 助教授 (80108191)
Project Period (FY) 1998 – 1999
Project Status Completed (Fiscal Year 1999)
Budget Amount *help
¥7,700,000 (Direct Cost: ¥7,700,000)
Fiscal Year 1999: ¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1998: ¥4,900,000 (Direct Cost: ¥4,900,000)
KeywordsGeomagnetic field / Paleosecular variation / Inverse problem / Dynamo simulation / 古地磁気データ / 古地磁気強度
Research Abstract

First of all, we examined the problem which arise because of the fact that paleomagnetic data are mostly given by inclination and declination, which depend nonlinearly on the parameters (Gauss coefficients) of the magnetic field model. Gubbins and Kelly (1993) and Johnson and Constable (1995, 1997) already published models of the time-averaged field for the last 5 million years. However, they implicitly assumed that there is a direct correspondence between the parameters and the data (I, D), which is not correct. By using the Taylor expansion method we showed that the mean of the nonlinear data depend not only on the means of parameters but on the variances of parameters. The variance of the data, on the other hand, depend only on the variance of the parameters, at the approximation to the second order terms.
Next, in order to avoid the complexity discussed above, we applied the inversion only to paleointensity data for the last 5 million years. Paleointensity data are usually accompani … More ed by the directional information, so that they can readily be converted to the three components (X, Y, Z) which are linear functions of the parameters. In this case, it is possible to solve the inverse problem separately for the means and for the variances. The results show that the mean magnetic field is more axial dipole like than the present field, and that largest nodipole power is contained in the (2, 1) harmonics. The inversion of variances resulted in a large g【0!1】 component, which is about 30% of the mean value. For other terms, unambiguous results were not obtained possibly because of the number of paleointensity data were not enough.
Thirdly, we developed a three-dimensional dynamo code in this research period and studied the origin of the geomagnetic field. Using the simulation results obtained by this code, we analyzed the behavior of dynamo magnetic field from the point of view of paleosecular variation. The comparison with the observed field show that dynamo field has many similar properties such as the dominance of the axial dipole component, about the same power on the surface of the core in harmonics of different degrees, and Gauss coefficients behave as random variates following zero-mean normal distributions. Other interesting properties such as the westward and eastward drift of surface features was seen only in the models. Less

Report

(3 results)
  • 1999 Annual Research Report   Final Research Report Summary
  • 1998 Annual Research Report
  • Research Products

    (20 results)

All Other

All Publications (20 results)

  • [Publications] Sakuraba, A., et al.: "Effect of the inner core on the numerical solution of the magnetohydro dynamic dynamo"Phys. Earth Planet. Inter.. Vol. 111. 105-121 (1999)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Udagawa, S., et al.: "Age and magnetism of lavas in Jokuldalur area, Eastern Iceland : Gilsa event revisited"Phys. Earth Planet. Inter.. Vol. 115. 147-171 (1999)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Tanaka, H.: "Circular symmetry of the paleomagnetic directions of served at low latitude volcanic sites"Earth Planets Space. Vol. 51. 1279-1286 (1999)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Kono, M. et al.: "Spherical harmonic inversion of paleomagnetic data : The case of linear mapping"J. Geophys. Res.. Vol. 105. 5817-5833 (2000)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Kono, M. et al.: "Dynamo simulation and paleosecular variation models"Phil. Trans. Roy. Soc. Lond.. A358. 1123-1139 (2000)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Sakuraba, A., et al.: "Deformation of vortex rolls in a rotating fluid spherical shell caused by an externally imposed magnetic field"Geophys. Astrophys. Fluid. Dynam.. (in press). (2000)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Sakuraba, A. and M. Kono: "Effect of the inner core on the numerical solution of the magnetohydrodynamic dynamo"Phys. Earth Planet. Inter.. 111. 105-121 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Udagawa, S., H. Kitagawa, A. Gudmundsson, O. Hiroi, T. Koyaguchi, H. Tanaka, L. Kristjansson, and M. Kono: "Age and magnetism of lavas in Jokuldalur area, Eastern Iceland : Gilsa Event revisited"Phys. Earth Planet, Inter.. 115. 147-171 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Tanaka, H.: "Circular asymmetry of the paleomagnetic directions observed at low latitude volcanic sites"Earth Planets Space. 51. 1279-1286 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Kono, M., H. Tanaka, and H. Tsunakawa.: "Spherical harmonic inversion of paleomagnetic data : The case of linear mapping"J. Geophys. Res.. 105. 5817-5833 (2000)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Kono, M., A. Sakuraba, and M. Ishida: "Dynamo simulation and paleosecular variation models"Phil. Trans. R. Soc. Lond.. A358. 1123-1139 (2000)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Sakuraba, A. and M. Kono.: "Deformation of vortex rolls in a rotating fluid spherical shell caused by an externally imposed magnetic field"Geophys. Astrophys. Fluid, Dynam.. (in press). (2000)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1999 Final Research Report Summary
  • [Publications] Kono, M.: "Spherical harmonic inversion of paleomagnetic data : The case of linear mapping"J. Geophys. Res.. Vol. 105, No. B3. 5817-5833 (2000)

    • Related Report
      1999 Annual Research Report
  • [Publications] Kono, M.: "Dynamo simulation and paleosecular variation models"Phil. Trans. Roy. Soc. Lond.. (in press). (2000)

    • Related Report
      1999 Annual Research Report
  • [Publications] Sakuraba, A.: "Deformation of vortex rolls in a rotating fluid spherical shell caused by an externally imposed magnetic field"Geophys. Astrophys. Fluid Dynam.. (in press). (2000)

    • Related Report
      1999 Annual Research Report
  • [Publications] Sakuraba,A.and M.Kono: "Effect of the inner core on the numerical solution of the magnetohydrodynamic dynamo" Phys.Earth Planet.Inter.(in press). (1999)

    • Related Report
      1998 Annual Research Report
  • [Publications] Kono,M., H.Tanaka, and H.Tsunakawa: "Spherical harmonic inversion of Paleomagnetic data: The case of linear mapping" J.Geophy.Res.(in press). (1999)

    • Related Report
      1998 Annual Research Report
  • [Publications] Udagawa,S., H.Kitagawa, ...and M.Kono: "Age and Magnetism of Lavas in Jokuldalur Area, Eastern Iceland: Gilsa Event Revisited" Phys.Earth Planet.Inter.(in press). (1999)

    • Related Report
      1998 Annual Research Report
  • [Publications] 桜庭 中,河野 長: "地球ダイナモの数値シミュレーション" 月刊地球. 20号. 288-292 (1998)

    • Related Report
      1998 Annual Research Report
  • [Publications] 河野 長: "“磁気工学ハンドフック",川西 健次・近角聡信・桜井良文偏" 「地球磁気現象」, 1204-1209 (1998)

    • Related Report
      1998 Annual Research Report

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Published: 1998-04-01   Modified: 2016-04-21  

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