Statistical Study on the Azimuthal Mode Number of Pc5 ULF Wave in the Inner Magnetosphere

Abstract

AbstractThe azimuthal mode number, m, of ultra‐low frequency (ULF) waves is a significant contributing factor for radiation belt electron energization, because it determines the conditions for resonant interaction between waves and particles. Based on multi‐point magnetic field measurements of GOES satellites from January to September of 2011, we statistically analyze the distributions of the characteristics of m of Pc5 ULF waves. In the dayside, the local peaks in the distributions of wave power spectra density locate at ∼10 and ∼13 MLT for m < 0 (westward propagation) and m > 0 (eastward propagation) waves respectively, suggesting the waves generally propagate anti‐sunward. In the nightside, the local peaks are at 22–23 MLT for both m < 0 and m > 0 waves, suggesting possible relation to substorm activities. Further investigation shows that, with increasing solar wind activities, the enhancements of dayside peaks are primarily contributed by |m| ≤ 3 waves, whereas the enhancements of nightside peak are contributed by both |m| ≤ 3 and |m| > 3 waves. With increasing AE index, the enhancements are more significant for the nightside peaks comparing to dayside peaks, and for |m| > 3 waves comparing to |m| ≤ 3 waves. The results of this study provide inputs for further investigation on the radial diffusion coefficient of radiation belt electrons with considering mode number information.