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Jiabei He

and 2 more

Lower-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 2014 to 2017 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 ∆f , chirping rate Γ, and maximum intensity Ia. Statistical results show typical properties of chorus waves: Ia ∼ 0.09 nT, ∆f ∼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 ∆f has positive correlation with β⊥ and fpe /fce. Normalized τ shows negative correlation with β⊥ and positive correlation with fpe /fce , respectively. Normalized Γ shows positive correlation with β⊥ and negative correlation with fpe /fce. These results help us better understand chorus waves excitation and their relation to the microburst.