Statistical properties of lower band rising tone chorus waves
Jiabei He, Zhiyang Xia, Lunjin Chen- Space and Planetary Science
- Geophysics
Abstract
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 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.
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