Daily variations of auroral kilometric radiation observed by STEREO

Abstract

Daily variations of terrestrial auroral kilometric radiation (AKR) are considered; an effect that is detected in STEREO/WAVES data. It has been found that the intensities of the AKR emitted from Northern and Southern sources are modulated with a period of ∼24 hours. The occurrence frequency of the AKR has been shown to be strongly dependent on the orientation of the rotating oblique magnetic dipole of the Earth relative to the Sun. AKR is found to occur more often and emit in a broader frequency range when the axis of the terrestrial magnetic dipole in the given hemisphere is oriented toward the nightside. We suggest that the observed ∼24 h variations of AKR are connected with diurnal changes of the ambient plasma density in the auroral region.