South Atlantic Anomaly

26°37′S 49°04′W / 26.61°S 49.06°W / -26.61; -49.06

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 (including the ISS) to higher-than-usual levels of ionizing radiation.

The effect is caused by the non-concentricity of Earth and its magnetic dipole and has been observed to be increasing in intensity recently. The SAA is the near-Earth region where Earth's magnetic field is weakest relative to an idealized Earth-centered dipole field.

Definition[edit]

The area of the SAA is confined by the intensity of Earth's magnetic field at less than 32,000 nanotesla at sea level,^[1] which corresponds to the dipolar magnetic field at ionospheric altitudes.^[2] However, the field itself varies in intensity as a gradient.^[1]^{: Figure 1}

Geomagnetic reversal

Geomagnetic storm

Large low-shear-velocity provinces

Operation Argus

Space weather

. BBC News. Section "Magnetic flip" contains a video showing the growth and movement of the South Atlantic Anomaly over the last 400 years.