A simple model for geomagnetic field excursions and inferences for palaeomagnetic observations

Abstract

We explore simple excursion scenarios by imposing changes on the axial dipole component of the Holocene geomagnetic field model CALS10k.2 and investigate implications for our understanding of palaeomagnetic observations of excursions. Our findings indicate that globally observed directions of fully opposing polarity are only possible when the axial dipole reverses: linearly decaying the axial dipole to zero and then reestablishing it with the same sign produces a global intensity minimum, but does not produce fully reversed directions globally. Reversing the axial dipole term increases the intensity of the geomagnetic field observed at Earth’s surface across the mid-point of the excursion, which results in a double-dip intensity structure during the excursion. Only a limited number of palaeomagnetic records of excursions contain such a double-dip intensity structure. Rather, the maximum directional change is coeval with a geomagnetic field intensity minimum.