Intense high-altitude auroral electric fields - temporal and spatial characteristics

Abstract. Cluster electric field, magnetic field, and energetic electron data are analyzed for two events of intense auroral electric field variations, both encountered in the Plasma Sheet Boundary Layer (PSBL), in the evening local time sector, and at approximately 5R_E geocentric distance. The most intense electric fields (peaking at 450 and 1600mV/m, respectively) were found to be quasi-static, unipolar, relatively stable on the time scale of at least half a minute, and associated with moving downward FAC sheets (peaking at ~10μA/m²), downward Poynting flux (peaking at ~35mW/m²), and upward electron beams with characteristic energies consistent with the perpendicular potentials (all values being mapped to 1R_E geocentric distance). For these two events in the return current region, quasi-static electric field structures and associated FACs were found to dominate the upward acceleration of electrons, as well as the energy transport between the ionosphere and the magnetosphere, although Alfvén waves clearly also contributed to these processes.