Cluster observations of ULF waves with pulsating electron beams above the high latitude dusk-side auroral region

Abstract

We report observations by the four Cluster satellites of particle acceleration associated with ULF (Alfvén) waves at an altitude of 6R_E above the dusk-side auroral region. All satellites observed upward accelerated ions and upgoing electron beams, which coincided with the upward field-aligned current around the plasmasheet boundary region. Here we study in detail one region of Alfvénic ULF waves observed together with upward electron beams, both having a quasi-periodicity of about 2 minutes. The ULF waves have a downward Poynting flux. Comparing data from different spacecraft, the observed electron beams are likely caused by the ULF waves in localized (0.5° latitude extension) flux tubes in the plasmasheet boundary region. The high-energy keV plasmasheet dispersive ion signatures showed similar periodicity, which suggests that the generation region of the ULF Alfvén waves is near the magnetospheric flank, and in turn induce time-varying particle energization.