“main ” — 2009/5/6 — 10:43 — page 243 — #1 Anais da Academia Brasileira de Ciências (2009) 81(2): 243-255(Annals of the Brazilian Academy of Sciences)ISSN 0001-3765www.scielo.br/aabc Time evolution of the South Atlantic Magnetic Anomaly

• Main Authors: Gelvam A. Hartmann, Igor G. Pacca
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Key words; geomagnetic field; non-dipole field anomalies; secular variation; South Pole; South pole; Siberia
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.652.6734; http://www.scielo.br/pdf/aabc/v81n2/v81n2a10.pdf

contributed by IGOR G. PACCA* 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 non-dipolar, 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.