The origin of the power‐law component in auroral electron spectra

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Abstract
Electron and ion data from the particle experiment onboard the VIKING spacecraft are examined in order to determine the origin of the power‐law component in auroral electron spectra. It is observed that at altitudes of ≈1 Re electron spectra peaked at a few keV are accompanied by a power law population in the energy range 10‐1000 eV that is usually thought to be composed of degraded primaries and secondary electrons of ionospheric origin.However, the presence of an ion beam at an energy of 1 keV flowing out of the ionosphere indicates the existence of a potential barrier between the location of the satellite and the ionosphere which would prevent secondary electrons of ionospheric origin from reaching the satellite altitude. Moreover, the angular characteristics of the low energy electrons indicate that this population moves downward and cannot be attributed to secondary and backscattered electrons coming out of the ionosphere. The spectral index k=1.7‐2 of the distribution function f ⧜ E−k for the power‐law electrons supports earlier theoretical findings that this population is formed in the auroral acceleration region by a combined action of a parallel electric field and waveparticle interactions.