The occurrence and characteristics of electron beams over the polar regions

Abstract

Data from the Lockheed experiment on the polar‐orbiting satellite S3‐3 have been used to study the morphology and some of the characteristics of narrow, field‐aligned electron beams. The beams were found to occur very commonly in a circumpolar zone corresponding to that of the statistical auroral oval. Upflowing, downflowing, and counterstreaming beams were found throughout the altitude range examined (3000–8000 km), but the variation of occurrence frequency with altitude depended on beam direction and indicated that the source region of the beams was commonly at or above 1 RE. The beams are characterized by a very narrow pitch angle distribution with a median half width at half maximum of 6° and by very soft energy spectra, and they were not usually detectable at energies above 400 eV. In contrast, their peak fluxes extended over a wide range, sometimes exceeding 1011 (cm² sr s keV)−1, although more usually they were less than 3×109 (cm² sr s keV)−1. Upflowing ions, especially ion conics, were commonly found in close association with the electron beams. It appears likely that several of the main features of the beams can be accounted for by a source model of a region of short‐lived multiple double layers.