View article

Ring current protons (<50 kev), which are unaffected by ion cyclotron waves outside the plasmapause, undergo strong turbulent diffusion just inside the plasmapause. Lifetimes from ion cyclotron turbulence are predicted to be of the order of 1 hour, as observed by Frank for 3≤L≤5. During the main phase of a geomagnetic storm, the protons rapidly diffuse across the plasmapause (probably at the Bohm rate) and are lost before reaching the noon meridian, thus giving rise to the asymmetric part of the ring current. During recovery phase the ring current decays on a time scale of a day or less, as the turbulent region moves outward with the expansion of the plasmapause. Further decay takes place on a charge exchange time scale.