Reflections on Geomagnetic Reversals

Abstract

Several investigators have noted that the Earth's magnetic dipole has been decreasing during the last century. Some have indicated that if the trend continues the dipole would be zero within a few thousand years, indicating that a reversal was occurring. Few if any take such suggestions seriously because of the weakness of the conditional if clause. An example of such a “prediction” is taken from the recent series of definitive models and reasons are given describing why such predictions of reversals are quite meaningless. It is known that the Earth's magnetic field, at the surface of the Earth is predominantly Bipolar. From paleomagnetic studies it is also known that this predominantly dipolar field has reversed its direction many times. Some studies indicate that although, at the present time, the dipole of the Earth is decreasing quite rapidly, the total magnetic energy outside the core is remaining nearly constant. This idea is reexamined using the recent definitive models and found to be true. The main purpose of this paper is to investigate the characteristics of relatively simple core sources which can produce the observed predominantly dipolar field and then cause the field to reverse without much loss of the total energy outside the core. A simple source in the outer core cannot produce the outstanding dipolar pattern that is observed. The right combination of many simple sources, the strongest of which must be very deep in the outer core, can create the dipolar pattern as has been shown in several previous studies. A very simple source system deep in the outer core is contrived to illustrate one way in which the main characteristics of a reversal can be realized.