Transient magnetic effects in a scale model of the earth's core.
Scale model experiments are described in which the contribution to the dipole magnetic field of a conducting sphere (simulating the earth's core) by initially closed, internal flux loops is measured. A magnetic loop is maintained by constant current in a toroidal coil, in a mercury sphere. The circuit is then opened, which allows the magnetic loop to diffuse and dissipate. The time development of the magnetic effects outside the sphere is recorded, especially the contribution in the dipole mode of the sphere. In a sample application of the result, a doughnut-shaped flux loop, of major and minor radii 0.17 and 0.053 R(c) (R(c) = earth's core radius) and centered at 0.68 R(c), of field strength 100 gauss, in optimal orientation and in a core of conductivity 3 x 10(-6) emu is assumed. If one such flux loop is set free on the average of every 40 years, the earth's dipole field is maintained. The relative intensity of the short-lived nondipole component that would accompany the process in the simplified example is estimated from the data and found not to be inconsistent with that observed in the real earth. Only the basic process of the feeding of a poloidal field by initially closed free flux loops in a static conducting sphere is investigated. The requirement that, in a real situation, the loops would have to be set free in a preferred orientation is discussed, and an existing model of a system that in some degree answers the requirement is cited.
Crane
H R
HR
Department of Physics, University of Michigan, Ann Arbor, Michigan 48109.