Abstract
Results of the first detailed study of simultaneously low-energy electron precipitation and optical auroral observations during quiet geomagnetic conditions in the evening side of the auroral oval, observed by the DMSP 32 satellite, are reported. The precipitation characteristics are different for different types of quiet auroral arcs. (1) Inside a faint diffuse aurora, equatorward of the oval, the six-point differential energy spectrum is characterized by nearly constant differential fluxes from 0.2 to about 8 keV with a sharp cutoff above 8 keV: the precipitated energy flux is about 0.1 erg/cm/sup 2/ s sr between 0.2 and 20 keV. (2) A faint discrete arc is characterized by a spectral peak (about 10/sup 8/-10/sup 9/ el/cm/sup 2/ s sr keV) near 0.5 or 1.2 keV superposed on a soft spectrum and an energy flux of a fraction of 1 erg/cm/sup 2/ s sr. (3) Inside a bright discrete quiet arc a distinct spectral peak near 3.2 keV with fluxes between 10/sup 7/ and 10/sup 8/ el/cm/sup 2/ s sr keV on a hard spectrum is observed; the precipitated energy flux is a few ergs/cm/sup 2/ s sr. (AIP)
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