A survey of low-energy (E≳5 KeV) electron energy fluxes over the northern auroral regions with satellite Injun 4

Abstract

Observations of the energy fluxes of ≳5-kev electrons at low altitudes (∼525–2500 km) over the northern auroral regions have been made by the nearly polar orbiting Injun 4 satellite, from February 1965 through July 1966, during a period of minimum solar activity. Results of the first detailed survey of the percentages of occurrence of the energy fluxes of ≳5-kev electrons (with pitch angles ∼40°±15°) in the outer radiation/auroral zone, as a function of magnetic local time and invariant latitude, are graphically displayed for various energy flux thresholds. The greatest occurrences of these energy fluxes were observed in the night-dawn-morning hours of local time, at latitudes from ∼65° to ∼70°, with median energy fluxes as great as 0.1 ergs(cm² sec sr)−1. The spatial distributions of these contours are compared with those for the occurrences of optical auroras. Limited simultaneous observations of these energy fluxes at pitch angles of ∼40° and ∼90° have shown that the ratios of these energy fluxes are typically greater than 0.1, with a condition of isotropy occurring for energy fluxes ≳1 erg (cm² sec sr)−1.