Upper mantle conductivity determined from the solar quiet day ionospheric currents in the dip equatorial latitudes of West Africa
The magnetic data obtained from a chain of ten magnetotelluric stations installed in the African sector during the international equatorial electrojet year (IEEY) was used to establish the 1993 quiet day current system (Sq) for West Africa and to determine the Earth’s upper mantle electrical co...
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| Autores principales: | , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
D.Ghitu Institute of Electronic Engineering and Nanotechnologies
2010
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/c5fc6974e60f44c585d1d352c9d5d559 |
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| Sumario: | The magnetic data obtained from a chain of ten magnetotelluric stations installed in the
African sector during the international equatorial electrojet year (IEEY) was used to establish
the 1993 quiet day current system (Sq) for West Africa and to determine the Earth’s upper
mantle electrical conductivity in the region. A spherical harmonic analysis (SHA) was applied
in the separation of the internal and external field/current contribution to the Sq variations,
while a special transfer function was used to compute the conductivity – depth values from
the paired external and internal coefficient of the SHA. The variation in the currents is seen to
be a dawn to dusk phenomenon with the variation in the external currents different from that
of the internal currents both in amplitude and in phase. The seasonal variation in the external
current maximizes during the March equinox and minimizes in the December solstice. The
conductivity had a downward increase with a high conductivity region spotted between
100 km and 205 km, which is seen to correspond to the seismic low velocity region. The conductivity at the upper mantle is seen to be 1.05 times higher than that obtained both in the
Asian (Himalayan) and Australian regions.
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