Measurements of precipitated 1–20 kev protons and electrons during a breakup aurora

Measurements of precipitating low‐energy (1–20 kev) protons and electrons during a breakup aurora are described. The observed proton fluxes were as high as 10 8 cm −2 sec −1 kev −1 ster −1 with a differential energy spectrum of the form E (kev) −3.2 ; the electron fluxes were ∼10 8 cm −2 sec −1 kev −1 ster −1 with a spectral peak in the 2–4 kev region. During the flight, the rocket passed through the poleward boundary of the auroral form. One interpretation of the data suggests that the proton and >2.5‐kev electron precipitation boundaries coincided to within a distance of <1 km; the lower energy electron boundary extended several kilometers poleward of the proton boundary. Evidence for nonisotropic proton fluxes is presented.