Satellite measurements of low‐energy electrons in the northern auroral zone

Particle flux measurements and radio and optical measurements on auroras were made concurrently with detectors aboard a polar orbiting satellite near the northern auroral zone. The incident particle energy deposition was measured in two shielded plastic scintillators with electron thresholds of 2 and 28 kev. Data were obtained for six satellite passes over the auroral zone, and for parts of four passes incident particle information was acquired simultaneously with optical and radio measurements. Large variations in the energy distribution of the precipitating particles were observed. On the basis of the assumption that the incident particles were all electrons, the maximum flux observed in the downward direction was determined to be approximately 100 ergs/cm2 sec ster of electrons with energy greater than 2 kev. The dominant energy contribution to the auroras was from electrons with energies less than 28 kev. Correlations with ground-based measurements showed that, in at least one rather unusual auroral form and in the regions of low-level luminosity outside discrete forms, electrons of energies less than a few kev carried a significant fraction of the precipitated energy.