Abstract
Because auroral luminosity and auroral absorption are produced mainly by electrons with different energy, simultaneous observation with photometer and riometer can give information about the energy spectrum of the incident electrons, and in particular be used to detect variations in this spectrum. Limited to cases with homogeneous auroral forms covering most of the sky, observations at λ5577 Å and 27.6 MHz show that the energy spectrum can remain constant for long periods, from half an hour to several hours and whole nights. Large and rapid variations do however occur, but less frequent than one could expect from satellite observations. This indicates that many variations in electron energy spectrum observed by satellite borne instruments are variations in space rather than variations in time. An average over three winters shows a diurnal variation in the energy spectrum with a hardening in the spectral shape between 20 and 01 local time. An unexpected high and variable light intensity corresponding to zero riometer absorption is also discussed.
Published Version
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