Statistical Analysis of Subpacket Structure in Isolated and Overlapping Chorus Elements

Abstract The rising tone chorus elements exhibit fine structures composed of multiple subpackets with varying amplitudes and durations. Using Van Allen Probes data and an automated detection algorithm, we identify 834831 lower band chorus elements, classify them into isolated and overlapping types, and statistically analyze their subpacket structure. During active geomagnetic conditions, isolated elements dominate on the nightside and dawnside, consistent with their shorter repetition times, whereas overlapping elements are relatively more common on the dayside because lower chirping rates extend element durations and allow neighboring elements to overlap. The amplitude and length of subpackets from isolated elements are inversely related, and the chirping rate decreases with subpacket length, both of which are consistent with nonlinear chorus wave growth theory. In contrast, even shorter subpackets may form due to overlapping chorus waves.