South Atlantic anomaly

A region of the Earth centered near 25S and 50W (near the Atlantic coast of Brazil) of low geomagnetic field intensity owing to the fact that the geomagnetic field axis is offset from the center of the Earth.  One consequence of the SAA is that trapped particles in the plasmasphere drift closer to the Earth’s surface and can more easily be lost into the atmosphere. The result is that the F region (see ionosphere) is highly variable in this region, and satellites in low Earth orbits suffer greater radiation doses when they pass through the SAA. There is a corresponding location of maximum geomagnetic field intensity in Southeast Asia.