AKR‐like emissions observed at low altitude by the DEMETER satellite

Abstract

This paper reports observations of Auroral Kilometric Radiation (AKR) by the low altitude satellite DEMETER (700 km) during the super magnetic storm of November 2004. AKR is generated along auroral field lines at altitudes above ∼3000 km and escapes from the Earth so that most observations have been made close to the source regions or at large distances from the Earth. However, EM waves with AKR‐like frequency spectra detected by the low altitude EXOS‐C satellite were interpreted by Oya et al. (1985) as AKR emissions propagating toward the Earth in the whistler mode. During the large magnetic storm of November 8–10, 2004, numerous events have been observed by DEMETER and, in one case, the emissions were recorded when DEMETER was flying over an intense aurora observed by the UVI (Ultra Violet Imager) of the POLAR spacecraft. During this event, density depletions have been observed at the satellite altitude. Similar AKR‐like EM waves were also recorded by DEMETER at other times showing that these emissions are a common phenomenon at low altitudes in the auroral regions during periods of sustained magnetic activity.