Optical emissions and ionization profiles during an intense pulsating aurora

Abstract

Coordinated spectrophotometric and incoherent scatter radar measurements were made of an intense early‐morning pulsating aurora at Chatanika, Alaska. Both instruments were operated simultaneously with temporal resolution of 1 s and were boresighted at geomagnetic zenith. The goals of the collaborative experiment were to determine the total energy flux Et and the characteristic energy parameter α of the precipitating electrons on a time scale smaller than the pulsation duration and to investigate the response of the ionospheric electron density on a comparable time scale. The relationship between total energy flux and the characteristic energy parameter suggests that during these observations the pulsations were caused by a modulation of α rather than by a modulation of the total precipitating particle flux. The values of Et and α derived from photometric data were used to model the electron density versus altitude in the ionosphere for comparison with the incoherent scatter radar measurements. Measured altitude profiles of ionization did not change significantly on the time scale of the pulsations. The E region maximum electron density typically was 7 × 105 at an altitude of 99 km. Variations in ionospheric conductivity were less than 15% on the pulsation time scale. These results suggest that a magnetospheric modulation mechanism is required to explain diffuse pulsating auroras.