Large airglow enhancements produced via wave‐plasma interactions in sporadic <i>E</i>

Abstract

In the past there has been great interest in monitoring enhanced 557.7 nm O(¹S) emissions from the thermosphere in connection with high‐power, high‐frequency (HF) radio wave modification of the F region ionosphere. These emissions are considered to be evidence that the HF‐modified electron distribution function is non‐Maxwellian because a significant flux of ∼5–6 eV electrons is required to produce the airglow. The suprathermal tail is believed to develop as a result of nonlinear plasma processes. Past F region observations of 557.7 nm airglow at Arecibo Observatory, Puerto Rico have yielded only a few Rayleighs of enhanced emissions. Recently, airglow enhancements were monitored in sporadic E above Arecibo. Surprisingly, these experiments yielded ∼55 Rayleighs of enhanced 557.7 nm airglow and the first observations of emissions from the N 2 first positive molecular bands. The observations imply that a large flux of energetic (5–10 eV) electrons is generated as part of the wave‐plasma interaction in sporadic E .