The 'convection surge' mechanism of ion acceleration during substorms

To explain the presence of the so-called 'bounce-phase-bunched' ion distributions (eV range to about 20 keV) observed in the earth's geosynchronous magnetosphere in association with substorm expansion phases, Quinn and Southwood proposed the 'convection surge' mechanism of ion energization. This mechanism is associated with a sudden earthward displacement of curved field lines resulting from the short-lived application of an intense, east-west electric field. A quantitative computer model of the mechanism has been constructed here. It is found that the mechanism easily generates the bounce-phase-bunched ion distributions in question. Additionally, the mechanism can generate dramatically field-aligned distributions. It is proposed that a key general characteristic of geosynchronous ion pitch angle distributions, field-aligned low energies, and field-perpendicular high energies is a signature of this energization mechanism. The presence of field-aligned ions cannot be presumed to be a signature of recent ionospheric extraction.