Statistical Characteristics of Chorus Second Harmonic Waves in the Earth's Inner Magnetosphere

Abstract

AbstractRecently, lower‐band chorus waves have been determined to cause diffuse auroral precipitation by exciting their second harmonics when the preferred excitation condition is satisfied. In this paper, with observations from the Van Allen Probe mission, we find that chorus second harmonic waves typically occur at L ∼ 4.5–6.5, particularly in the night‐dawn‐noon sector, which is consistent with the distribution of electron diffuse aurora. This observation suggests that chorus second harmonics play a potential role in the generation of diffuse aurora. Additionally, although most second harmonic events of chorus waves are found near the preferred excitation condition under the cold plasma assumption, in our survey, a secondary group is found away from the preferred excitation condition. The deviation is attributed to the significant alteration of the dispersion curve by the contribution from thermal electrons. Our results are helpful for understanding the excitation of chorus second harmonics and their roles in the magnetosphere.