Abstract
Paleomagnetic studies clearly show that the polarity of the magnetic fi eld has been subject to reversals. It is generally assumed that polarity intervals are exponentially distributed. Here, the geomagnetic polarity reversal record, for the past 166 Ma, is analysed and a new approach to the study of the reversals is presented. In detail, the occurrence of 1/f-noise in the Power Spectral Density (PSD), relative to geomagnetic fi eld reversals, the existence of a Zipf's law behaviour for the cumulative distribution of polarity intervals, and the occurrence of punctuated equilibrium, as shown by a sort of Devil's staircase for the reversal time series, are investigated. Our results give a preliminary picture of the dynamical state of the geomagnetic dynamo suggesting that the geodynamo works in a marginally stable out-of-equilibrium confi guration, and that polarity reversals are equivalent to a sort of phase transition between two metastable states.
Highlights
At the beginning of the last century, the French scientists P
In the last three decades, growing interest has been devoted to many natural phenomena that are characterised by Power-Law Distributions (PLDs)
In order to check the occurrence of punctuated equilibrium for geomagnetic reversals we introduced a surrogate «Accumulated Activity» AA(t) as t
Summary
Paola De Michelis and Giuseppe Consolini of these reversals it is possible to try to gain information on gradually changing conditions at the core-mantle boundary. Taking into account that reversal sequences are not stationary and that a reversal requires a finite amount of time, one can think that there has to be some statistical correlation between the lengths of successive polarity intervals In this case, the process cannot be truly Poisson and it has been shown (Naidu, 1971; Phillips, 1977) that a gamma distribution could provide a better fit to the observed intervals. One possible answer to the geomagnetic field time reversals debate is to describe these events as typical nonlinear behaviour of a highly complex dynamical system especially if one takes into account that nonlinear systems are capable of a vast range of responses. In this picture we investigated the possible occurrence of Zipf’s law, 1/f noise, and punctuated-equilibrium in the geomagnetic polarity reversals, analysing all reversal data back to about 166 Ma ago
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