OBSERVATIONS OF ELECTRON-BEAMS IN THE LOW-LATITUDE BOUNDARY-LAYER

This paper describes and interprets measurements made of electrons in the energy range 10 ev to 2 kev during 1977 and 1978, using the vector electron spectrometer (VES) on the spacecraft ISEE 1 in the low latitude boundary layer (LLBL) on the sunward side of the magnetosphere. Observations of the electron distribution functions there indicate that the plasma population of the layer, in addition to contributions from the magnetosheath and magnetosphere, frequently shows evidence of field aligned electron beams in the energy range approximately 100 ev. The frequency, strength, and stability of the beams in the LLBL are assessed. Finally, the possibilities for the origin of these beams are discussed, and it is suggested that they may be identified with those recently observed at altitudes above approximately 1 R//E.