Cover: Variations in the Geomagnetic Field and in the Rate of the Earth's Rotation.

Variations in the Geomagnetic Field and in the Rate of the Earth's Rotation.

by Richard Henry Ball, Anne B. Kahle, Ernest H. Vestine


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Investigation of the hypothesis that variations in the earth's (mantle) rate of rotation are balanced by changes in the angular momentum of the core, as inferred from geomagnetic data on motion of the eccentric dipole (westward-drifting magnetic center of the earth). Improved data and the fact that the earth is now in a slow phase provide an opportunity to confirm the indications of previous work that there exists a correlation between variations in the length of the earth's day and the motion of the geomagnetic eccentric dipole. The observed lag in phase between the mantle and the magnetically inferred core motion can be explained by diffusion of the core magnetic signal through the conductivity of the mantle, which conversely gives an independent estimate of mantle conductivity. The suggested mantle conductivity required to account for the eccentric dipole lag is consistent with estimates from other sources; however, estimates of eccentric dipole velocity should more directly relate to the angular momentum of the outer core. 33 pp. Refs. (CC)

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