| Project/Area Number |
05640468
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体地球物理学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
TAKEDA Masahiko Kyoto University, Faculty of Science, Technical Officer, 理学部, 教務職員 (30236484)
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| Project Period (FY) |
1993 – 1994
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| Project Status |
Completed (Fiscal Year 1994)
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| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1994: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1993: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Keywords | External Geomagnetic Variation / Oceanic Electric Currents / Earth's Interior / Electric Conductivity / Geomagnetic Daily Variation / 地球内部電気伝導度 / 誘導電流 |
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| Research Abstract |
Internal terms of the geomagnetic variation fields are often used to estimate the electrical conductivity distribution in the Earth. However, conductivity of the ocean (4S/m) is much larger than that of the shallow part of the solid Earth (10^<-2>-10^<-4>S/m) , and thus currents induced by the variation of the external fields are much affected by the distribution of the ocean. Of cource, the effects depend on both the spatial and time scale of the external field, but geomagnetic solar quiet daily variation fieid (Sq) and geomagnetic disturbance field called Dst or Dp of less than a few days period are affected by the currents in the ocean because time constant of the currents induced in the ocean is about 10 hours.
In the present study, first currents induced in the ocean by the Sq field and Dp and Dst fields of the periods from one hour to a few days were globally simulated using spherical harmonics, and geomagnetic field variation at several observatories by the currents were estimated. It was found that the currents for the Dst field are weaker than those for the Sq or Dp fields of the same period. This is because the Dst field requires zonally flowing induced currents which are largely obstructed by the continents. Next, finer distribution of the induced currents around Japan was obtained. In the method detailed sea-land distribution is considered and the effects of the self inductance is treated self-consistently, and the values of the induced currents calculated globally are used as the boundary conduction. The resultant induced field estimated by only land-sea distribution will be used as a standard for anomalous distribution of the conductivity.
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