Energy spectra of precipitating electrons from observations of optical aurora, Bremsstrahlung X rays, and auroral absorption

Simultaneous balloon observations of auroral N2+ (λ3914) emission and bremsstrahlung X rays produced by the precipitation of energetic electrons in the auroral zone suggest that two distinct groups of electrons are responsible for the observed effects. One group is responsible for the major portion of the total precipitated energy during visible aurora, and at times this group not only provides the dominant flux of X rays below about 40 kev but also accounts for most of the cosmic noise absorption. A remarkable feature of this group is the extent to which its average energy may vary, i.e., from several kev to greater than 25 kev during the post-midnight hours. A second group of particles is responsible for the X ray flux above 50 kev; however, the total power deposited in the atmosphere by this group is seldom greater than a few tenths erg cm−2 sec−1. The spectrum of these electrons can be represented by a simple exponential function with an e folding energy usually between 40 and 65 kev. A recognition of these features of the spectrum leads to a better understanding of the relationship between optical, X-ray, and auroral absorption events.