The auroral electron energy spectrum extended to 45 ev

Direct measurements of the precipitated auroral electron energy spectrum above 1 kev indicate that the differential energy spectrum has a peak near 6 kev [Mcllwain, 1960; Albert, 1967; Evans, 1968]. This spectrum has been referred to in the literature as a monoenergetic electron beam, and theoretical models of the source mechanism have been developed accordingly [e.g., Taylor and Hones, 1965], It is the purpose of this Letter to report a recent observation of this auroral electron spectrum extended to 45 ev, which reveals the existence of a smooth continuum from which the 6-kev peak emerges to produce the auroral arcs. These observations were obtained from the Rice University Javelin Twins 1 sounding rocket experiment which was launched to an altitude of 800 km over an active IBC I-II aurora from Fort Churchill, Manitoba, at 2347 local time, March 17, 1967. The auroral conditions during the flight consisted of a general diffuse glow of about 5 kR (3914 A) with a system of arcs of more than 25 kR (3914 A), which moved across the payload trajectory.