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

Abstract

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.

High‐resolution spectra of 20‐300 Kev hard X‐rays from electron precipitation over Antarctica

“…et at., 1975] and spectra With two exponential components, hard and soft, have also been observed[Christensen and Karas, 1970]. Even• i is the only event where the onset'is observed, that is, in adjacent 15-rain spectra the X-ray spectra went from background to a detectable predpitation flux.…”

Magnetospheric substorms on September 14, 1968

“…Figure 6 shows plots of the integral electron fluxes measured at Vela and at ATS 1 and calculated from the X-ray flux at the balloon for three times, 0930, 0933, and 0935 UT, just before and during the 'spike.' (An incident electron spectrum was derived from the measured X-ray spectrum using the method of Christensen and Karas [1970]). The calculated electron fluxes above the balloon at 0933 and 0935 are indicated by two straight-line segments because the X-ray data suggested that the incident electron flux at those times could best be represented as a superposition of two exponential spectra.…”