What the Swarm mission may tell us about the South Atlantic Anomaly

The South Atlantic Anomaly (SAA) is often simply mapped using total intensity values taken from spherical harmonic models of the Earth's magnetic field. These models are derived from magnetic field observations taken by satellites and observatories and it is expected that data from the forthcoming Swarm mission will make a significant contribution to them. However, the location of the SAA as it affects Low Earth Orbiting (LEO) satellites is more completely determined by considering charged particle trajectories in the Earth's magnetic field. To include the effects of solar wind variations and magnetic storms, dynamic radiation belt models are used, and they generally assume that the Earth's magnetic field is dipolar. In order to quantify the effect of the omission of the non-dipolar terms and how it is changing with time, we calculate loss cones for trapped particles in the SAA region at typical LEO altitudes using a full spherical harmonic model and a simplified dipolar model. We also compare the results with SAA peak locations through time as derived from the alongtrack scanning radiometer series of instruments on board the ERS-1, ERS-2 and ENVISAT satellites.