Non-monotonic growth and motion of the South Atlantic Anomaly

Hagay Amit,Maxime Lézin,Ricardo I Trindade,Filipe Terra-Nova

doi:10.1186/s40623-021-01356-w

Abstract

The South Atlantic Anomaly (SAA) is a region at Earth’s surface where the intensity of the magnetic field is particularly low. Accurate characterization of the SAA is important for both fundamental understanding of core dynamics and the geodynamo as well as societal issues such as the erosion of instruments at surface observatories and onboard spacecrafts. Here, we propose new measures to better characterize the SAA area and center, accounting for surface intensity changes outside the SAA region and shape anisotropy. Applying our characterization to a geomagnetic field model covering the historical era, we find that the SAA area and center are more time dependent, including episodes of steady area, eastward drift and rapid southward drift. We interpret these special events in terms of the secular variation of relevant large-scale geomagnetic flux patches on the core–mantle boundary. Our characterization may be used as a constraint on Earth-like numerical dynamo models.

Highlights

The South Atlantic Anomaly (SAA) is a region at Earth’s surface where the intensity of the magnetic field is low
Understanding the past and present locations and mobility as well as the future trajectory of the SAA is both a fundamental scientific challenge—it involves understanding the working of the geodynamo and the impact of core–mantle coupling on core dynamics, as well as an important societal issue—it has major consequences for the operation and protection of surface instruments and spacecrafts, from global positioning systems to the Hubble Space Telescope, which cannot obtain observations over the SAA region
The current location of the SAA center in Brazil is related to the location of reversed geomagnetic flux patches (RFPs) at the core–mantle boundary (CMB) (Bloxham et al 1989; Olson and Amit 2006) though this relation is not trivial (Terra-Nova et al 2017)

Summary

Introduction

The South Atlantic Anomaly (SAA) is a region at Earth’s surface where the intensity of the magnetic field is low. The current location of the SAA center in Brazil is related to the location of reversed geomagnetic flux patches (RFPs) at the core–mantle boundary (CMB) (Bloxham et al 1989; Olson and Amit 2006) though this relation is not trivial (Terra-Nova et al 2017). It is under debate whether the current SAA location represents a persistent boundary-driven feature of Earth’s magnetic field or it is chaotically variable. Based on archeological materials, it was argued that the SAA has influenced the surface geomagnetic field for several millennia in Africa (Tarduno et al 2015; Hare et al 2018) and South America (Trindade et al 2018; Hartmann et al 2019). Tarduno et al (2015) used such local intensity and directional timeseries, together with observation of a Large Low Shear Velocity Province (LLSVP) in the lowermost mantle below Africa coincident with a historical African RFP on the CMB (e.g. Jackson et al 2000), to propose that core flux expulsion occurred preferentially

Methods

Findings

Conclusion