Magnetopause boundary structure deduced from the high-time resolution particle experiment on the Equator-S spacecraft

An electrostatic analyser (ESA) onboard the Equator-S spacecraft operating in coordination with a potential control device (PCD) has obtained the firs t accurate electron energy spectrum with energies approximate to 7 eV-100 e V in the vicinity of the magnetopause. On 8 January, 1998. a solar wind pre ssure increase pushed the magnetopause inward, leaving the Equator-S spacec raft in the magnetosheath, On the return into the magnetosphere approximate ly 80 min later, the magnetopause was observed by the ESA and the solid sta te telescopes (the SSTs detected electrons and ions with energies approxima te to 20-300 keV). The high time resolution (3 s) data from ESA and SST sho w the boundary region contains of multiple plasma sources that appear to ev olve in space and time. We show that electrons with energies approximate to 7 eV-100 eV permeate the outer regions of the magnetosphere, from the magn etopause to approximate to 6Re. Pitch-angle distributions of approximate to 20-300 keV electrons show the electrons travel in both directions along th e magnetic field with a peak at 90 degrees indicating a trapped configurati on. The IMF during this interval was dominated by Bx and By components with a small Bz.