The South Atlantic Anomaly (SAA) is an area where Earth's inner Van Allen radiation belt comes closest to Earth's surface, dipping down to an altitude of 200 kilometres (120 mi). This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher-than-usual levels of ionizing radiation. The effect is caused by the non-concentricity of Earth and its magnetic dipole. The SAA is the near-Earth region where Earth's magnetic field is weakest relative to an idealized Earth-centered dipole field.