Cluster observations of energetic ionospheric ion beams in the auroral region: Acceleration and associated energy-dispersed precipitation

[1] This paper presents a detailed study of the Feb. 14, 2001 Cluster northern auroral pass at mid-altitudes (4–5 RE), characterized by observations of a series of energy-dispersed ion structures in a region of poleward convection. In contradiction with one current view, that ions populating these energy-dispersed signatures originate sporadically in the magnetotail, Cluster directly observed energetic (0.2–15 keV), field-aligned H+ ions of ionospheric origin. The ions were ejected at the top of a steady auroral acceleration region near 72.5° ILAT, then bounced on closed field-lines, and were finally dispersed poleward in latitude by the E × B drift effect. Simple but realistic latitudinal drift computations demonstrate that the anticipated location of successive bouncing echoes coincides rather well with the Cluster observations. Best agreement is reached when the particles are further accelerated (presumably nonadiabatically) by 1–2 keV, as they periodically cross the tail neutral sheet.