Abstract
Few geomagnetic ground observations exist of the Earth's strongest core field anomaly, the South Atlantic Anom- aly (SAA). The geomagnetic repeat station on the island Tristan da Cunha, located half-way between South Africa and South America at 37° 05' S, 12° 18' W, is therefore of crucial importance. We have conducted several sets of repeat station measurements during magnetically quiet conditions (Kp 2o or less) in 2004. The procedures are de- scribed and the results are compared to those from earlier campaigns and to the predictions of various global field models. Features of the local crustal bias field and the solar quiet daily variation are discussed. We also evaluate the benefit of continuous magnetic field recordings from Tristan da Cunha, and argue that such a data set is a very valuable addition to geomagnetic satellite data. Recently, funds were set up to establish and operate a magnetome- ter station on Tristan da Cunha during the Swarm magnetic satellite mission (2011-2014).
Highlights
One of the largest gaps in the current distribution of geomagnetic ground observations is in the South Atlantic Ocean
It is the weakening of the geomagnetic field in the South Atlantic Anomaly (SAA) that is in large part responsible for the present decline of Earth’s magnetic field strength (Olsen et al, 2006, Hulot et al, 2007)
A consequence of the low geomagnetic field intensity is the distortion of the inner van Allen radiation belt, causing a strong increase of radiation damage to low-Earth-orbiting satellites when passing through the SAA (Heirtzler et al, 2002)
Summary
One of the largest gaps in the current distribution of geomagnetic ground observations is in the South Atlantic Ocean (fig. 1). The SAA originates from inverse magnetic flux patches at the coremantle boundary mainly beneath South America and South Africa, which have developed over the last 200 years (Gubbins et al, 2006). It is the weakening of the geomagnetic field in the SAA that is in large part responsible for the present decline of Earth’s magnetic field strength (Olsen et al, 2006, Hulot et al, 2007).
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