Bursty energetic electrons confined in flux ropes in the cusp region

Bursty energetic electron events with energies of about 20– 400 keV have been observed in the cusp region when the CLUSTER S/C were travelling outbound on 5 April 2001. These electron events are characterized by strong impulsive increases in the flux whereas energetic ions (>30 keV) show no obvious changes. The enhanced energetic electron flux is more than 10 times higher than the background level whereas the energetic ions show no significant changes. The bursts of energetic electrons occurred mainly in the time interval when the northward IMF had a significant B y component and were associated with the rotation of the local B z (bi-polar signature) and with a dramatic change of the plasma flow (