Analysis of the Duration of Rising Tone Chorus Elements

TitleAnalysis of the Duration of Rising Tone Chorus Elements
Publication TypeJournal Article
Year of Publication2017
AuthorsTeng, S, Tao, X, Xie, Y, Zonca, F, Chen, L, Fang, WB, Wang, S
JournalGeophysical Research Letters
Date Published12/2017
Keywordschorus element duration; DAWN; frequency chirping rate; Van Allen Probes
AbstractThe duration of chorus elements is an important parameter to understand chorus excitation and to quantify the effects of nonlinear wave-particle interactions on energetic electron dynamics. In this work, we analyze the duration of rising tone chorus elements statistically using Van Allen Probes data. We present the distribution of chorus element duration (τ) as a function of magnetic local time (MLT) and the geomagnetic activity level characterized by auroral electrojet (AE) index. We show that the typical value of τ for nightside and dawnside is about 0.12 s, smaller than that for dayside and duskside by about a factor of 2 to 4. Using a previously developed hybrid code, DAWN, we suggest that the background magnetic field inhomogeneity might be an important factor in controlling the chorus element duration. We also report that τ is larger during quiet times and shorter during moderate and active periods; this result is consistent with the MLT dependence of τ and the occurrence pattern of chorus waves at different levels of geomagnetic activity. We then investigate the correlation between τ and the frequency chirping rate (Γ). We show that, from observation, τ scales with Γ as math formula, suggesting that statistically the frequency range of chorus elements (τΓ) should be roughly the same for different elements. These findings should be useful to the further development of a theoretical model of chorus excitation and to the quantification of nonlinear wave-particle interactions on energetic electron dynamics.
URLhttp://onlinelibrary.wiley.com/doi/10.1002/2017GL075824/full
DOI10.1002/2017GL075824
Short TitleGeophys. Res. Lett.


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