Field-aligned electrons at the lobe/plasma sheet boundary in the mid-to-distant magnetotail and their association with reconnection

摘要

We have surveyed field-aligned electrons at the lobe/plasma sheet boundary and their association with reconnection in the distant magnetotail where reconnection is quasi-steady and large scale. Asymmetric (in energy) counterstreaming electrons are detected in similar to 30% of the boundary crossings when high-speed flows are present in the plasma sheet. In 98% of the electron beam cases the low-energy electrons are directed toward and the higher-energy electrons directed away from the X-line. The well-organized (by the signs of B-x and V-x) quadrupolar pattern of the electrons indicates that these electrons are associated with reconnection. The low-energy electrons could be the outer part of the Hall current loop, similar to previous reports in the near-Earth region. The mean electron energy in the distant tail is a factor of ten lower than in the near Earth tail. Our observations suggest that the Hall effect can be detected even at large distances from the diffusion region.