South Atlantic Anomaly

This is a huge electromagnetic sink in the van allen belt; it is bigger than Brazil.

Here's nice overview.

Earth can be viewed as a gigantic bar magnet spinning in space. Its toroidal magnetic field encases the planet like a huge inner tube. This field shields Earth from the solar wind—a continuous stream of charged particles cast off by the sun. It also traps charged particles, which tend to congregate in distinct bands based on their charge, energy, and origin. Two primary bands of trapped particles exist: the one closer to Earth is predominantly made up of protons, while the one farther away is mostly electrons. Evidence of these bands was first made public by James Van Allen, and so they are often referred to as the Van Allen radiation belts. This radiation can cause all sorts of malfunctions in spacecraft electronics. In fact, the Geiger counter used to measure cosmic rays on Explorer 1 stopped functioning because it was overloaded by radiation!