The testing of geomagnetic reversal models: recent developments

• Published in: Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1982
• Subjects: Geomagnetic Pole
• Online Access: http://dx.doi.org/10.1098/rsta.1982.0075; https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.1982.0075

The number of available palaeomagnetic records displaying detailed transitional field behaviour has increased significantly over the past few years. The expanded data set of transitions now includes records of sequential reversals from the same site locality as well as multiple recordings of a particular reversal from widely separated sites. Such data are most useful with regard to the testing of geomagnetic reversal models. First, records of successive reversals may make it possible to distinguish whether transitional fields originate primarily with the configurational characteristics of the reversing geodynamo or whether a non-reversing portion of the field is responsible. Such an analysis does not yet provide conclusive evidence in support of either hypothesis. Second, multiple records from distant sites furnish the best possible data with regard to the determination of the harmonic content of particular transitional fields. In this regard, two quite independent, testable models have been applied to the several recordings of the Matuyama-Brunhes transition. Findings support the hypothesis that the intermediate field geometry during this particular polarity transition was indeed controlled by non-dipole zonal harmonic terms. Moreover, analysis of the paths of the virtual geomagnetic pole associated with the available records strongly suggests that the most extreme dominance of transitional fields by axisymmetric components occurs during the onset of the reversal, a finding that now has support on purely theoretical grounds. Finally, field behaviour associated with existing igneous-recorded palaeomagnetic excursions is not unlike that observed at the onset of field reversals. Hence, there is growing evidence in support of the hypothesis that attempts by the geodynamo to reverse are not always successful. These recordings of apparent abortive reversals may be of considerable value with regard to our understanding of transitional fields and geomagnetic reversal.