Statistical Properties of Lower Band Rising Tone Chorus Waves

Abstract

AbstractLower‐band chorus waves are known to play dual roles in radiation belt dynamics (electron acceleration and precipitation), and understanding their properties and excitation is very important. A systematic study of chorus waves properties in terms of background plasma parameters (electron perpendicular beta β⊥ and the ratio of plasma frequency to electron cyclotron frequency fpe/fce) has not been performed previously. We use burst‐mode data from Van Allen Probe A from 2012 to 2019 and develop an algorithm to extract individual lower band rising tone chorus elements. We statistically analyze four properties of rising tone chorus elements: time duration τ, frequency width Δf, chirping rate Γ, and maximum amplitude Ia. Statistical results show typical properties of chorus waves: Ia ∼ 0.09 nT, Δf ∼ 0.08fce, Γ ∼ 2 × 103 Hz/s, τ ∼ 0.015–0.25 s. On the nightside and dawnside, Γ shows wider spread and is more distributed over larger values, which is associated with the wider distribution of β⊥. Chorus waves at duskside and dayside have larger values of τ, associated with smaller β⊥ and larger fpe/fce. The dependence of chorus wave properties on background plasma parameters is also examined. We show that normalized Δf has positive correlation with β⊥ and fpe/fce. Normalized τ shows negative correlation with β⊥ and positive correlation with fpe/fce. Normalized Γ and Ia show positive correlations with β⊥ and negative correlations with fpe/fce. These results help us better understand chorus waves excitation and their relation to the microburst.