Conductive Geodynamo: A Global Circuit Model Using Dual Disc Dynamos
Abstract
A single disc conductive dynamo has been introduced earlier to illustrate the generation of the earth's magnetic field. However, it is believed that such a dynamo embedded in a nearly spherical earth core would be short-circuited and would not support self-sustained dynamo action. This general belief has directed recent focus to fluid-convective motions of the core as a dominant and necessary source for the geodynamo. This paper reports the contributions of the conductive electrical currents in the core. Contrary to prior belief, a conductive dynamo can be operative in the earth core. The global circuit model has been developed using a stacked set of two dual-disc systems simulating the northern and southern global hemispheres. This conductive dynamo has provided some answers heretofore unavailable from convective dynamos. The key findings are as follows: (1) Conductive dynamos lead to a near constant magnetic field: The conductive current induced in the core cannot increase indiscriminately by the self-generated magnetic field. The temperature dependence of the earth core resistance, in effect, limits the current to about ~10E13 amps. A saturation effect sets in and limits the self-excited magnetic field to nearly constant levels (about 3 gauss and 1,000 gauss for dipole and toroidal fields, respectively, in the core). (2) They obtain dynamo energy from the earth's rotation: The Ohmic heating of approximately 10E14 watts is derived from the rotational energy of the earth. The Lorentz forces on the conductive electrons in the dynamo come directly from the earth's rotation. (3) They provide self-sustained conditions without a fluid core: A small part of the Lorentz-force driven current is converted into azimuthal current (about 10E9 amps), which is responsible for the dipole magnetic field. There are two main sources for this conversion: a Hall effect and the rotational component of the conductive currents. The physical model and computational methods used in this investigation were based upon a simplified dual dynano model. We strongly recommend further investigation of this conductive dynamo system with the resources, methodologies and extensive computational facilities being applied to convective dynamo research.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMGP31A0170W
- Keywords:
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- 0619 Electromagnetic theory;
- 1500 GEOMAGNETISM AND PALEOMAGNETISM;
- 1507 Core processes (8115);
- 1510 Dynamo theories