Correlations between low‐frequency and high‐frequency auroral kilometric radiation plasma wave intensity bursts and X rays in the auroral zone

Abstract

Comparisons are made between X‐ray (>2 keV) emissions emanating from the Earth's Northern Hemisphere aurora observed on the Polar satellite and auroral kilometric radiation (AKR) plasma wave intensities detected on the Geotail satellite. For this comparison the plasma wave frequencies were divided into a low‐frequency (LF‐AKR) (30–100 kHz) band and a high‐frequency (HF‐AKR) (100–800 kHz) band. For the LF‐AKR band the correlation coefficients with auroral X‐ray emissions are generally high and significantly larger than the corresponding coefficients between X‐ray and HF‐AKR variations. It is found that short time‐scale variations of the LF‐AKR activity often correspond to the temporal fine structure of the intensity (5–10 min) of X‐ray auroral emissions. HF‐AKR intensity enhancements generally precede enhancements of the X‐ray emissions, while the LF‐AKR intensity enhancements generally lag the X‐ray enhancements. This sequence implies that auroral acceleration begins at lower altitudes and then moves to higher altitudes. In addition, the time profiles of the X‐ray intensities often display slower recovery times than do the LF‐AKR.