The plasmapause, the plasma sheet, and energetic trapped electrons in the earth's magnetosphere

Abstract

Observations from the IMP 2 satellite show that much of the energetic trapped radiation observed near the equatorial plane lay beyond the plasmapause, which therefore cannot be the boundary between ‘open’ and ‘closed’ field lines in the Earth's magnetosphere. The position of peak intensity for electrons >45 keV generally lay just beyond the plasmapause, while the position of peak intensity for electrons >l.6 MeV lay just inside it. The ‘slot’, the position of minimum intensity between inner and outer radiation belts lay well inside the plasmapause for both 1.6 MeV and 45 keV electrons. The boundary between the stable trapping zone and the ‘distant’ radiation zone of highly fluctuating particle fluxes which also lay beyond the plasmapause, near 10 R s during quiet times moved as close to the Earth as 6 R s shortly after onset of magnetic bays; these positions are close to those reported for the inner boundary of the plasma sheet. It is suggested that: (1) The plasmapause is the limiting magnetic shell at which most terrestrial plasma of ionospheric origin can remain trapped, if there is an electric field across the magnetosphere. (2) The inner boundary of the plasma sheet is the limiting distance to which the more energetic interplanetary plasma can penetrate into the Earth's field under the action of the same magnetospheric electric field.