Geophysical Research Letters

Observations of earthward streaming electrons at the trailing boundary of a plasmoid



In this paper, we report on highly asymmetric spectrum of electrons observed at the boundary of postplasmoid plasma sheet (PPPS). The data were obtained when GEOTAIL made repeated crossings of the boundary after encountering with a tailward flowing plasmoid at XGSM ∼ −46RE. In the spectrum, electrons in 0.1–1 keV energy range are seen to flow earthward along the lobe-like field lines into the PPPS counter to more energetic components (ions and electrons) leaking from the PPPS. In the boundary region, earthward streaming electrons are observed even when the energetic leaking components almost disappear, which makes us characterize this region more generally by tailward flowing field aligned currents (FAC). By referring to hybrid code (ion particles, massless electron fluid) results, we propose that the earthward flowing electrons sustain the FAC away from the X-line (tailward if a spacecraft is located tailward of the X-line), which is a part of a Hall current loop built-up in the course of magnetic reconnection.