Physics
Scientific paper
Nov 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989pepi...57..284g&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 57, Issue 3-4, p. 284-290.
Physics
10
Scientific paper
The geomagnetic polarity reversal record, for the past 165 Ma, is analysed for evidence of chaotic dynamics by searching for fractal scaling exponents in the statistical distribution of polarity intervals. The test involves counting the number of polarity intervals longer than a given cutoff size as a function of the cutoff size and plotting the results on log-log coordinates. The resulting graph does suggest a straight line pattern (i.e., `scaling' with an exponent roughly equal to -1.5) over a fairly large cutoff range (0.5-10 Ma) and could be interpreted as evidence for lack of an intrinsic time-scale in the dynamical processes leading to reversal. However, it is shown that a non-stationary Poisson model (the prevailing view of the statistics of polarity intervals) easily predicts such scaling and that it is arising from the trend toward longer intervals near the Mid-Cretaceous. Therefore the scaling does not warrant special significance here even though low-dimensional chaos has sometimes been advocated for the geodynamo based on the chaotic reversals of current flow in coupled disc-dynamo models. It is suggested that the long-term trend or non-stationarities in reversal rate may pose difficulties for the demonstration of chaos in the reversal record, as it has for other statistical questions concerning the record, such as interval independence and periodicities.
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