Electron transitions and propagation characteristics of dipolarization fronts observed by cluster

This thesis describes electron transitions at the dipolarization fronts (DPFs) observed by Cluster using high time-resolution data. The sharp electron transitions occur within the rising phase of the magnetic field component Bz normal to the magnetotail current sheet. The electron transitions provide a new constraint on the DPFs generation models that are related to reconnection. A sudden Bz rise without a small dip prior to the increase was observed suggesting that tearing instabilities in the reconnection exhaust may not be required for the generation of DPFs. Based on timing and minimum variance analysis, the DPFs are found to have a curved structure and propagate earthward. The results in this study are consistent with DPFs being the injection fronts from the reconnection exhaust.