Relating the South Atlantic Anomaly and geomagnetic flux patches

Research areas:
South Atlantic Anomaly
Physics of the Earth and Planetary Interiors
Abstract The South Atlantic Anomaly (SAA) is a region of weak geomagnetic field intensity at the Earth’s surface, which is commonly attributed to reversed flux patches (RFPs) on the core-mantle boundary (CMB). While the \{SAA\} is clearly affected by the reversed flux region below the South Atlantic, we show that the relation between the intensity minimum at Earth’s surface and \{RFPs\} is not straightforward. We map a field-dependent intensity kernel Constable, 2007 to study the relation between the radial geomagnetic field at the \{CMB\} and the field intensity at Earth’s surface. Synthetic tests highlight the role of specific patches in determining the surface intensity minimum and demonstrate that the \{SAA\} can indeed be explained by a few intense patches. Supported by these synthetic tests, our analysis highlights the role of specific flux patches (reversed and normal) in determining the location of the \{SAA\} minimum. We show that the level of axial dipolarity of the field determines the stability of the relation between the \{SAA\} minimum and RFPs. The present position of the \{SAA\} minimum is determined by the interplay among several robust geomagnetic flux patches at the CMB. The longitude of the \{SAA\} minimum appears near the longitude of the Patagonia \{RFP\} due to the low-latitude normal flux patches (NFPs) near Africa and mid-Atlantic which diminish the effect of the Africa RFPs. The latitude of the \{SAA\} minimum is lower than the Patagonia \{RFP\} latitude due to the South Pacific high-latitude \{NFP\} and the axial dipole effect. The motion of the \{SAA\} minimum is explained by the motions and changes in intensity of these robust geomagnetic flux patches. Simple secular variation (SV) scenarios suggest that while the \{SAA\} path can be explained by advection, its intensity decrease requires magnetic diffusion. In addition these \{SV\} scenarios provide some speculative predictions for the SAA.