INHIBITION AND GEOMAGNETIC-FIELD REVERSALS

Analysis of the geomagnetic reversal chronology indicates a positive correlation between reversal rate and reversal inhibition. Such a correlation is to be expected between reversal rate and any inhibition resulting from the fact that a reversal transition requires a finite time. The very nature of the way that reversal chronologies are constructed dictates the existence of an interval of about 5000 years, following the initiation of a successful reversal, during which the probability of observing a further reversal is zero. Modeling indicates that the observed estimates of inhibition are consistent with an interval of depressed probability much longer than this. OUT preferred model is that reversals are triggered by internal instabilities of the fluid motion of the core and that, after the (approximately) 5000-year interval required for successful reversal of the direction of the magnetic field, the probability for further reversals gradually recovers to its initial value over an interval of about 45,000 years. We suggest that this recovery period is related to subsequent diffusion of the magnetic field in the core. A corollary of this interpretation is that it is possible to make a rough estimate of the electrical conductivity of the core fluid from paleomagnetic data. The estimated value is 6 x 10(5) S m-1.