Statistical Properties of Lower Band Rising Tone Chorus

Lower-band chorus is known to play dual roles (electron acceleration and precipitation) in radiation belt dynamics. A systematic study of chorus 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 Wide Frequency Receiver waveform data from Van Allen Probe A from 2014 to 2017 and develop an algorithm to extract individual chorus elements. We statistically analyze four properties of rising tone chorus elements: time duration τ, bandwidth Δf, chirping rate Γ, and average intensity Ia. Statistical results show typical properties of chorus waves: Ia ∼0.09nT, Δf ∼0.08fce, Γ ∼2×103 Hz/s, τ ∼0.015-0.25s. The MLT dependence is examined. On the nightside and dawnside, normalized Δf, Γ, and τ show wider spread, which is associated with the wider distribution of β⊥. Chorus at duskside and dayside have larger values of τ, associated with a narrow distribution of β⊥. The dependence of chorus wave properties on background plasma parameters is also examined. We show that normalized τ is shorter when β⊥ and fpe/fce increase, while normalized Δf and Γ increase with β⊥ and fpe/fce. These results are important for understanding chorus wave excitation and properties of resulting microburst.