Relationship between energy flux Q and mean energy 〈E〉 of auroral electron spectra based on radar data from the 1987 CEDAR Campaign at Sondre Stromfjord, Greenland

Abstract

The incoherent scatter radar at Sondre Stromfjord, Greenland, measured electron density profiles from 90 to 500 km during four auroral events over a 3‐hour period on February 28, 1987. The profiles were obtained with the radar pointed along the magnetic field near zenith at 15‐s intervals. Under the assumption that proton/H atom precipitation was unimportant during these events a representation of the incident electron flux was obtained by fitting calculated profiles with measured profiles in the vicinity of their peaks (lower E region). Maxwellian and Gaussian electron distributions with high‐ and low‐energy tails were used to generate the calculated profiles. The distributions were specified in terms of average energy 〈E〉 and energy flux Q. We find that we can clearly distinguish between profiles that result from a Maxwellian incident electron spectrum and those that result from a Gaussian spectrum. Interpreting Gaussian and Maxwellian spectra as representative of discrete and diffuse aurora, respectively, the measurements indicated good correlation between 〈E〉 and Q for discrete aurora, while essentially no correlation was observed for diffuse aurora. This is consistent with current understanding that discrete auroras are produced by electrons accelerated by magnetic field‐aligned potential drops whereas diffuse auroras are produced by pitch angle diffusion of plasma sheet electrons into the loss cone.