Analysis of the Last Reversal, Last Excursions and important HoloceneAnomalies of the Geomagnetic Field using the Eccentric Dipole and a 360-Dipole Ring Mode

Eccentric dipole can be considered the next approximation of the geomagnetic field after the
generally used geocentric dipole. Considering that during reversals, excursions and important
anomalies the non-dipole contributions are relevant, we study the evolution of the eccentric
dipole during the last reversal (Matuyama-Brunhes transition, ~780 ka), last excursions
(Laschamp, ~41 ka and Mono-Lake, ~34 ka), the Levantine Iron Age Anomaly (LIAA, ~1000 BC)
and the South Atlantic Anomaly (SAA, from 700 AD to present day) according to
paleoreconstructions (IMMAB4, LSMOD.2, SHAWQ-Iron Age and SHAWQ2k, respectively). In
order to get as much as information as possible from the eccentric dipole, we design a simple
model based on 360-point dipoles evenly distributed in a ring close to the Inner Core Boundary
that can be reversed and/or changed their magnitude. We calculate the evolution of the
modeled eccentric dipole according to the 360-dipole ring model reproducing the eccentric
dipole from the paleoreconstructions. If we consider that each point dipole could be associated
to convective columns in the outer core of the Earth, we can relate the evolution of the eccentric
dipole with potential variations in the outer core that cause its displacement. We observe that
the modeled eccentric dipole moves away from regions where dipoles start to reverse (which
are the cases for the reversal, excursions and the SAA) and towards regions where there are
anomalous high-moment dipoles (such as the LIAA). The results show that the eccentric dipole
paths during the events studied correlate well to Core Mantle Boundary low heat flux regions
that is consistent with the development of instabilities in the geomagnetic field.