Low-frequency electric field fluctuations and field-aligned electron beamsaround the edge of an auroral acceleration region

Electron beams narrowly collimated to the magnetic field line were observed continuously from a downward current region to an auroral acceleration reg ion (i.e., upward current region). They were well correlated with low-frequ ency electric field fluctuations in the auroral acceleration region as well as in the adjacent downward current region. Magnetic field fluctuations we re found only in the downward current region. The analysis suggests that st atic field-aligned electric fields are not fully responsible for the filed- aligned electron acceleration; the ac electric field, presumably associated with Alfvenic fluctuations, should also be involved in the acceleration of ionospheric electrons.