South Atlantic Anomaly

The South Atlantic Anomaly (or SAA) is the region where Earth's inner van Allen radiation belt makes its closest approach to the planet's surface. The result is that, for a given altitude, the radiation intensity is higher over this region than elsewhere. The SAA is alleged to be produced by a "dip" in the Earth's magnetic field at that location, caused by the fact that the center of Earth's magnetic field is offset from its geographic center by 450 kilometers (280 miles) . Some believe that the anomaly is a side effect of Geomagnetic reversal.
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