Cassini Plasma Spectrometer observations of bidirectional lobe electrons during the Earth flyby, August 18, 1999

Unlike previous missions to the magnetotail (IMP 6, ISEE 1, ISEE 3, and Geotail), which effectively made observations in the lobe at a single downtail distance, the Cassini Earth swingby allowed, for the first time, near-continuous observations covering a range of downtail distances. Bidirectional electrons are found in the northern lobe, consistent with previous studies. Enhancements in the electron fluxes are seen in a boundary layer between the lobe and sheath. These enhancements are accompanied by enhancements in ion fluxes traveling tailward. We also present what we believe to be the first observations of a returning electron population in the magnetosheath. Bidirectional electrons are observed upto 0.02 keV, while at higher energies only unidirectional electrons are observed. The low energy of the returning electrons arises as a. result of the electron populations' passage through the magnetopause twice and losses due to precipitation.