Unraveling the excitation mechanisms of highly oblique lower band chorus waves

TitleUnraveling the excitation mechanisms of highly oblique lower band chorus waves
Publication TypeJournal Article
Year of Publication2016
AuthorsLi, W, Mourenas, D, Artemyev, AV, Bortnik, J, Thorne, RM, Kletzing, CA, Kurth, WS, Hospodarsky, GB, Reeves, GD, Funsten, HO, Spence, HE
JournalGeophysical Research Letters
Pagination8867 - 8875
Date Published09/2016
Keywordsbeam instability; lower band chorus; oblique chorus excitation; temperature anisotropy; Van Allen Probes
AbstractExcitation mechanisms of highly oblique, quasi-electrostatic lower band chorus waves are investigated using Van Allen Probes observations near the equator of the Earth's magnetosphere. Linear growth rates are evaluated based on in situ, measured electron velocity distributions and plasma conditions and compared with simultaneously observed wave frequency spectra and wave normal angles. Accordingly, two distinct excitation mechanisms of highly oblique lower band chorus have been clearly identified for the first time. The first mechanism relies on cyclotron resonance with electrons possessing both a realistic temperature anisotropy at keV energies and a plateau at 100–500 eV in the parallel velocity distribution. The second mechanism corresponds to Landau resonance with a 100–500 eV beam. In both cases, a small low-energy beam-like component is necessary for suppressing an otherwise dominating Landau damping. Our new findings suggest that small variations in the electron distribution could have important impacts on energetic electron dynamics.
Short TitleGeophys. Res. Lett.

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