Cluster Observations of the Most Energetic Electron Event Associated with Earthward and Tailward Flows

The formation of energetic electrons in relation to high speed flows in magnetotail has been observed by multiple missions. Here we focus on the formation of most energetic electron events. The physical mechanism how they are accelerated is still unclear. We report one of the most energetic electron events of the Cluster mission observations. The very high flux of  energetic electrons is observed at about 10 Re in magnetotail, associated with bursty bulk flows and rebound flows as observed by different Cluster spacecraft separated on the fluid scale. Understanding this event helps us better demonstrate how most energetic electrons are accelerated in the magnetotail. However, due to the limitation of large fluid-scale separation of the spacecraft, we can not address the physical mechanisms at the small ion scales, that is critical for understanding the energetic electron acceleration mechanisms.  We speculate how future multi-scale observations would allow us to make significant improvement in our understanding of the physics of energetic electron acceleration.