Abstract
The South Atlantic Magnetic Anomaly (SAMA) is one of the most outstanding anomalies of the geomagnetic field. The SAMA secular variation was obtained and compared to the evolution of other anomalies using spherical harmonic field models for the 1590-2005 period. An analysis of data from four South American observatories shows how this large scale anomaly affected their measurements. Since SAMA is a low total field anomaly, the field was separated into its nondipolar, quadrupolar and octupolar parts. The time evolution of the non-dipole/total, quadrupolar/total and octupolar/total field ratios yielded increasingly high values for the South Atlantic since 1750. The SAMA evolution is compared to the evolution of other large scale surface geomagnetic features like the North and the South Pole and the Siberia High, and this comparison shows the intensity equilibrium between these anomalies in both hemispheres. The analysis of non-dipole fields in historical period suggests that SAMA is governed by (i) quadrupolar field for drift, and (ii) quadrupolar and octupolar fields for intensity and area of influence. Furthermore, our study reinforces the possibility that SAMA may be related to reverse fluxes in the outer core under the South Atlantic region.
Highlights
The morphology and time variation of the geomagnetic field result from magnetohydrodynamic processes that take place in the Earth’s outer core
The study of the main characteristics of the field observed at the Earth’s surface, together with their variations in historical and geological time scales, has enabled the elaboration of numerical geodynamo simulations that have been successful in providing explanations for features of the field such as its predominantly dipolar character, secular variation and field reversals (e.g. Glatzmaier and Roberts 1995a, b, Kageyama et al 1995, Kageyama and Sato 1997, Kuang and Bloxham 1999)
South Atlantic Magnetic Anomaly (SAMA) shows a westward drift, and predictions of its variations have been made based on a linear extrapolation (Heirtzler 2002), but they are rather approximate and do not reflect the current configuration of the geomagnetic field
Summary
The morphology and time variation of the geomagnetic field result from magnetohydrodynamic processes that take place in the Earth’s outer core. Another remarkable feature of the geomagnetic field is the Siberia High, a region where field intensities are considerably higher than those for comparable latitudes. Show how the SAMA variation affected measurements of four South American observatories, the non-dipolar source character of the South Atlantic magnetic field, and the relation between SAMA and other geomagnetic anomalies. The high degree terms that correspond to the non-dipole fields have been increasing significantly, indicating the importance of these terms for SAMA
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call