Electron dynamics in the reconnection ion diffusion region

Abstract

We investigate and compare Cluster observations of electron dynamics in different locations of the ion diffusion region for magnetic reconnection in the Earth's magnetotail. On the basis of the 2‐D reconstructed magnetic field map from Cluster 1 (C1), we pinpoint that the observed Hall field is ∼6000 km (∼9 ion inertial lengths) away from the magnetic X‐point, and reveal that C3 was the one in closest proximity to the X‐point at the time when the reconnection jet reversal was simultaneously seen by three spacecraft, namely, C1, C3, and C4. No evidence is found for strong wave emission and energetic electron enhancement near to the X‐point, as compared to that within the diffusion region. We find that (1) the Hall current loop is mainly carried by the low‐energy, field‐aligned counterstreaming electrons; (2) a flat‐top distribution in phase space density is a common feature for Hall‐related electrons; (3) an enhancement of energetic electrons is observed together with the presence of the flat‐top electrons; and (4) electromagnetic wave emission is enhanced within the diffusion region. Two different regions of field‐aligned counterstreaming (FC) electrons are identified: one is associated with the Hall current loop (i.e., the electron flow reversal) while another one stays at the edge of the loop. Interestingly, observations show that at the transition between the two FC regions, the waves seem to suppress the energetic electrons but to promote the flat‐top electrons.