The Earth's core

Abstract

The modern view of the origin of the geomagnetic field associates it with motions in the liquid core of the Earth. This new approach, suggested by W. Elsasser, hasled to a revival of interest in the main geomagnetic field and phenomena connected with it. The hypothesis of motions in the Earth's core not only accounts for the remarkably rapid changes in the geomagnetic field but also for the irregular fluctuations in the rate of rotation of the Earth. E. C. Bullard has given convincing arguments for the belief that these motions in the Earth's core arise from thermal convection. It may easily be demonstrated that the motions are to a high degree dominated by the Coriolis forces arising from the Earth's rotation. Consequently model experiments on thermal convection under the influence of Coriolis forces are of great importance in understanding the physics of the Earth's core. Such experiments, done by R. Hide of the Department of Geodesy and Geophysics of Cambridge University, give rise to an interesting explanation of the westerly drift of the geomagnetic field, discovered by E. H. Vestine, and give patterns of motion involving jet streams, which are incidentally of remarkable similarity to the motions in the upper atmosphere. The essentially two‐dimensional motions which result from the dominance of the Coriolis forces are thought to supply a fundamental reason for the axial character of the geomagnetic field. Though much is known about the physical processes in the core relating to the geomagnetic field, the mechanisms by which these motions set up electromotive forces are still obscure, though two lines of approach look promising. The first is that the motions maintain the field by a dynamo action and the second is that they set up temperature distributions which give rise to thermoelectric currents.