Field line topology determined by energetic particles during a possible magnetopause reconnection event

Abstract

The September 8, 1978, crossing of the magnetopause by ISEE 1 and 2 has been studied in the light of energetic ion and electron data in order to derive the magnetic field topology. The plasma and magnetic field observations during this crossing provided evidence for the occurrence of plasma acceleration intrinsic to reconnection between interplanetary and magnetospheric magnetic field lines. The energetic particle observations result in two different pictures of the open and closed field lines within the magnetosphere, depending on either the ion or electron observations. According to the ion measurements, the high‐speed flow can be placed exclusively on open field lines. The electrons, however, exhibit trapped distributions during these times. This apparent dilemma can be resolved by invoking magnetic mirroring of the electrons off the increased magnetosheath field, as shown in a companion paper by Daly and Fritz (1982).