Evolução do campo geomagnético no período pré e pós-surgimento da anomalia magnética do Atlântico Sul

Abstract

Earth’s magnetic field extends into space and is predominantly dipolar. It plays a critical role in sustaining life by partially shielding the planet from electrically charged particles emitted by the Sun. Over the past few centuries, a region of low magnetic field intensity has emerged in southern Africa, migrated across the South Atlantic Ocean, and recently reached South America. This feature, known as the South Atlantic Magnetic Anomaly (SAMA), represents an area where the geomagnetic field is weaker. To investigate the past behavior of Earth’s magnetic field, mathematical models can estimate geomagnetic elements over time and space. In this study, the CALS10k.2 and IGRF-13 models were employed to analyze the evolution of geomagnetic Field intensity at the surface and at altitude from 1000 to 2024, focusing on the SAMA. The analysis involved evaluating the temporal evolution of the SAMA’s center and área relative to the global average geomagnetic field intensity outside the anomaly. The results revealed that the point of lowest geomagnetic field intensity across Earth's surface, currently identified as the SAMA’s center, was located over the Indian Ocean in the year 1000. This point shifted to the South Atlantic Ocean around 1130, which was defined in this study as the onset of the SAMA. Moreover, analyses incorporating the global variation of the geomagnetic field outside the anomaly indicated that the point of lowest intensity does not always coincide with the anomaly's center of mass, particularly during periods when the SAMA's area becomes more asymmetric. When defining the SAMA’s area based on the global average geomagnetic intensity outside the anomaly, a slower rate of area variation was observed over time compared to the traditional criterion, which typically relies on a fixed intensity contour to delineate the anomaly. This suggests that using a fixed threshold may overestimate fluctuations in the SAMA’s area over time. Additionally, geomagnetic field analyses at varying altitudes demonstrated that the SAMA's features become progressively smoother at higher altitudes, reflecting the diminished influence of non-dipolar components and the predominance of the dipolar field. Finally, if the SAMA’s trends over the past two centuries persist, the associated effects of intensified particle fluxes will likely expand over a larger area, amplifying the potential impacts.