Magnetic reconnection has long been regarded as an important site for producing energetic electrons in solar terrestrial and astrophysical plasmas. The motivation of this paper is to provide the average properties of energetic electrons in reconnection region, which are crucial for understanding electron energization mechanism but are rarely known. We statistically analyzed the energetic electrons through 21 magnetotail reconnection events observed by Cluster spacecraft during the years of 2001–2005. Approximately 1200 data points with time resolution of 8 s have been collected for each spacecraft. Two parameters are examined: energetic electron rate (EER) and power law index. EER, which is defined as the ratio of the integrated energetic electron flux to the lower energy electron flux, is used to quantify the electron acceleration efficiency. We find that EER and energetic electron flux (EEF) are positively correlated with the power law index, i.e., the higher rate and flux generally corresponds to softer spectrum. This unexpected correlation is probably caused by some nonadiabatic heating/acceleration mechanisms that tend to soft the spectrum with high temperature. EER is much larger within the earthward flow than the tailward flow. It is positively correlated with the outflow speed Vx, while the correlation between EER and Bz is less clear. With the increment of earthward outflow speed, the occurrence rate of high EER also monotonically increases. We find that EER generally does not increase with the increment of perpendicular electric field |E⊥|, suggesting that adiabatic betatron and Fermi acceleration probably play minor roles in electron energization during magnetotail reconnection.

Recent studies show that the out-of-plane quadrupolar magnetic field in fast magnetic reconnection is distorted in the presence of a guide field. It is asymmetric with respect to the current sheet. In this work, we analyze the spatial and amplitude asymmetries of the Hall magnetic field 𝐵𝑦 and the Hall electric field 𝐸𝑧 in reconnection with different guide fields by a series of 2.5-D particle-in-cell simulations. We derive the relation between the asymmetry of 𝐵𝑦 and 𝐸𝑧 and the guide field strength. In addition, by analyzing the different terms in the generalized ohm's law, we find that the electric field 𝐸𝑧 is mainly balanced by the Hall term, and the amplitude asymmetry is mainly caused by the Hall effect.