Earth's Collapsing Dipole in the Context of Long-term Geomagnetic Field Behavior

Over the time interval for which direct geomagnetic field measurements have been made the strength of the geomagnetic dipole has been monotonically decreasing, at the rate of several percent per century. The significance of this decrease (collapse?) must be considered in the light of what is known about geomagnetic field behavior over longer timescales, behavior which includes mean strength, variance, and temporal correlation, in addition to the rates of occurrence of and time taken to accomplish individual geomagnetic reversals. Paleomagnetic data suggest that the decreasing trend has been present at least since 1000~AD, although estimation of the actual dipole moment becomes increasingly difficult as one goes further back in time because of sparse temporal and spatial data coverage. However, it is also abundantly clear from paleomagnetic data that the present dipole is not anomalously low, and that even if it were, extreme DIPs (Decreases in Paleointensity) are not necessarily accompanied by full geomagnetic reversals. Such DIPs may nevertheless have important influences on Earth's immediate magnetic environment. This

work adopts a statistical approach in attempting to answer the following questions: Is the next geomagnetic reversal overdue? Is the current rate of decrease of the dipole moment anomalously large? Is the variance in the geomagnetic field related to reversal rate? What does the spectrum of secular variation look like? Paleomagnetic datatsets drawn from times that include

both low and high reversal rates are evaluated in the context of Gaussian statistical models for paleosecular variation.