Abstract
Prior to the observation of fast tailward plasma flows, earthward plasma flows are often observed in the distant magnetotail. By studying the evolution of the ion distribution functions for the transition flow from earthward to tailward flow, we find a multi-layer structure of beam-like plasma flows in the plasma sheet boundary layer, PSBL: 1) earthward, anisotropic beam plasma can be observed in the outer region of PSBL, i.e., the plasma lobe side of the PSBL; and 2) the counterstreaming ions, which consist of earthward and tailward beam-like plasma flows, are observed in the inner region of the PSBL; i.e., the plasma sheet side. Inside the plasma sheet, an isotropic, hot ion plasma can be observed. These characteristics are similar to those measured in the PSBL closer to the Earth, and the tailward anisotropic ion beams observed in the near-Earth magnetotail are thought to be the mirrored counterpart of the earthward ion beam. In the distant magnetotail, however, it is not easy to explain the tailward beam as the mirrored counterpart, because the reflected ion beams at the Earth will be absorbed into the plasma sheet before the reflected ions can travel to the distant magnetotail. We propose another model of two active magnetic reconnection sites. The tailward ion beams come from a near-Earth reconnection site which is embedded in the distant magnetotail reconnection site ejecting the earthward flow.
