Favorable conditions for energetic electron acceleration during magnetic reconnection in the Earth’s magnetotail

摘要

We have studied favorable conditions for energetic electron acceleration during magnetic reconnection in the Earth’s magnetosphere using the Geotail data. We have found the strong energetic electron acceleration in some reconnection events. On the other hand, the other reconnection events show weak electron acceleration. To discuss what reconnection characteristics determine energetic electron acceleration efficiency, we have studied the reconnection characteristics for 10 events in which the Geotail satellite observed the vicinity of the diffusion region. We have classified the relationship between the reconnection characteristics and the electron acceleration efficiency into three types: (1) good correlation (absolute value of correlation coefficient ∣r∣ > 0.6); (2) ambiguous correlation (0.6 > ∣r∣ > 0.3); and (3) no correlation (0.3 > ∣r∣). We found that ion heating, electron heating, current sheet thickness, reconnection electric field, and converging normal electric field could be categorized into good correlation. Ion/electron temperature ratio, total amount of reconnected magnetic energy, and reconnection rate were classified in ambiguous correlation. We could not find any correlation between energetic electron acceleration efficiency and absolute value of outflow velocity, current density parallel to magnetic field (Hall current system), and satellite location in the Earth’s magnetosphere. From our analysis we claimed that the electrons are efficiently accelerated in a thin current sheet during fast reconnection events.