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

Abstract

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