Changing Geomagnetic Field from the Ionosphere to the Core-Mantle Boundary

In this study two aspects of the geomagnetic field have been investigated. The first part focuses on perturbations of the external field, as seen by the CHAMP satellite and predicted by the Thermosphere-Ionosphere Electrodynamic General Circulation Model, for the purpose of helping to separate out ionospheric sources from the ambient geomagnetic field using a physics based approach. Part two looks at variations of the internal field through an examination of the South Atlantic Anomaly. The NCAR Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIE-GCM) is a self-consistent, global, atmospheric model that can be used to estimate magnetic perturbations at satellite altitude. These computed perturbations can then be compared with the magnetic vector data provided by low-earth orbiting satellites. Analogous CHAMP magnetic vector residuals were computed for these intervals using the CHAOS model to remove the core and crustal geomagnetic contributions. Under various input parameters, the TIE-GCM predictions were compared with the CHAMP residuals on an orbit by orbit basis demonstrating a reasonable agreement between the TIE-GCM estimates and the CHAMP residuals in non-polar, dayside regions (±50° magnetic latitude). Although no clear component or temporal correlation was discerned, evidence showing overall residual decrease in the comparisons presents the possibility of using the TIE-GCM to preprocess geomagnetic data for main field modeling purposes. A group of spherical harmonic field test models, developed utilizing this correction, verify the feasibility of this application. Variations of the internal field are investigated through study of the South Atlantic Anomaly, a region of low geomagnetic field measured at the Earth's surface. The time evolution of this feature is tracked at the surface over the last 400 years. Subsequently, its associations with the axial dipole moment and radial geomagnetic flux are examined at the core-mantle boundary, revealing in the process, a possible link between total unsigned flux and geomagnetic jerks.