A Phase-Transition Model for Geomagnetic Polarity Reversals

Abstract

It is generally considered that the polarity reversal intervals have an exponential distribution. We have examined the distribution using all reversal data back to about 165 m.y. ago, and found that this distribution follows a power-law rather than an exponential. Power laws are common in critical phenomena, and therefore we propose that the geodynamo is marginally stable and that the geomagnetic polarity reversal is a kind of critical phenomenon. We present a simple model in which turbulent eddies in the outer core are assumed to behave as magnetic spins. By numerical simulation, we found that intervals of polarity reversals in the model follow a power-law at a critical state. When the energy dissipation accompanying polarity reversals is taken into account, the model self-organizes to the critical state.