Observing, Modeling, and Interpreting Magnetic Fields of the Solid Earth

Abstract

Many Earth system processes generate magnetic fields, either primary magnetic fields or in response to other magnetic fields. The largest of these magnetic fields is due to the dynamo in the Earth's core, and can be approximated by a geocentric axial dipole that has decayed by nearly 10% during the last 150 years. This is an order of magnitude faster than its natural decay time, a reflection of the growth of patches of reverse flux at the core-mantle boundary. The velocity of the North magnetic pole reached some 40 km/yr in 2001. This velocity is the highest recorded so far in the last two centuries. The second largest magnetic field in the solid Earth is caused by induced and remanent magnetization within the crust. Controlled in part by the thermo-mechanical properties of the crust, these fields contain signatures of tectonic processes currently active, and those active in the distant past. Recent work has included an estimate of the surface heat flux under the Antarctic ice cap. In order to understand the recent changes in the Earth's magnetic field, new high-quality measurements are needed to continue those being made by Ørsted (launched in 1999), CHAMP and the Ørsted-2 experiment onboard SAC-C (both launched in 2000). The present paper is motivated by the advent of space surveys of the geomagnetic field, and illustrates how our way of observing, modeling, and interpreting the Earth's magnetic field has changed in recent years due to the new magnetic satellite measurements.

Toward a better representation of the secular variation. Case study: The European network of geomagnetic observatories

“…An inspection of sources that contribute the observed geomagnetic field at Earth's surface reveals the well known three main contributors, namely the core field (also called the main field), the lithospheric field and the external field (Mandea and Purucker, 2005;Olsen et al, 2007). They are produced, respectively, by a dynamo process in the outer core, by the magnetized rocks above the Curie temperature in the lithosphere and by the interaction of solar radiative and particle output with the ionosphere and magnetosphere.…”

The magnetic field changing over the southern African continent: a unique behaviour

“…Separating these contributions is not an easy task (e.g. Mandea and Purucker, 2005;Maus and Lühr, 2005;Maus et al, 2006;Olsen et al, 2006;Thomson and Lesur, 2007). However, using a spherical harmonic expansion of the geomagnetic field potential, a separation between internal and external contributions to the field can be obtained.…”

“…In addition, the highly uneven coverage of the globe by magnetic observatories also makes their study difficult (e.g. Mandea and Purucker, 2005).…”

The Origin of Mercury’s Internal Magnetic Field

“…In the ocean area, striped anomalies are associated with sea-floor spreading; this pattern is characterized by a nearly constant magnetization direction over many hundreds of km and can be correlated with the dipole reversal sequence over millions of years. More details on magnetic field contributions of internal origin can be found in Mandea and Purucker (2005).…”