Observations of an upward‐directed electron beam with the perpendicular temperature of the cold ionosphere

The Freja TESP electron spectrometer has repeatedly observed ∼100 eV ‐ 1 keV upward‐directed, anti‐field‐aligned electron beams near 1700 km altitude in the auroral zone. A particularly intense event, at energies up to 2 keV, is described. The beam perpendicular temperature T ⟂ e was as low as 0.1–0.2 eV at 100–200 eV parallel energy. The 10–15 s period of upward fluxes was coincident with a low density (∼10 cm −3 ) period and a ∼5 keV ion conic. Strong low frequency waves and the lack of any downward motion in the simultaneously observed ion conic suggest a strong element of wave acceleration, while electric field and ion loss cone measurements provide limited evidence of potential acceleration to a fraction of the observed energies.