Large 6300‐Å airglow intensity enhancements observed in Ionosphere Heating Experiments are excited by thermal electrons

Abstract

It is shown that the 6300‐Å airglow intensity enhancements observed in ionosphere heating experiments, by high‐power HF waves, which have been hitherto attributed to excitation by energetic electrons accelerated in plasma instabilities, are excited by energetic electrons from the tail of the heated thermal (maxwellian) electron gas. In addition, a plausible explanation for the inadequacy of the electron temperatures observed in the early ionosphere heating experiments at Arecibo to account for the observed oxygen red line enhancements is presented. In the light of these developments, electron acceleration in ionosphere HF heating experiments might be more scarce than is commonly believed.