Compressional ULF wave modulation of energetic particles in the inner magnetosphere

TitleCompressional ULF wave modulation of energetic particles in the inner magnetosphere
Publication TypeJournal Article
Year of Publication2016
AuthorsLiu, H, Zong, Q-G, Zhou, X-Z, Fu, SY, Rankin, R, Wang, L-H, Yuan, CJ, Wang, YF, Baker, DN, Blake, JB, Kletzing, CA
JournalJournal of Geophysical Research: Space Physics
Date Published05/2016
KeywordsCompressional ULF wave; energetic particles; Magnetosphere; Mirror effect; Modulation; relativistic electrons; Van Allen Probes
AbstractWe present Van Allen Probes observations of modulations in the flux of very energetic electrons up to a few MeV and protons between 1200 − 1400 UT on February 19th, 2014. During this event the spacecraft were in the dayside magnetosphere at L⋆≈5.5. The modulations extended across a wide range of particle energies, from 79.80 keV to 2.85 MeV for electrons and from 82.85 keV to 636.18 keV for protons. The fluxes of π/2 pitch angle particles were observed to attain maximum values simultaneously with the ULF compressional magnetic field component reaching a minimum. We use peak-to-valley ratios to quantify the strength of the modulation effect, finding that the modulation is larger at higher energies than at lower energies. It is shown that the compressional wave modulation of the particle distribution is due to the mirror effect, which can trap relativistic electrons efficiently for energies up to 2.85 MeV, and trap protons up to ≈600 keV. Larger peak-to-valley ratios at higher energies also attributed to the mirror effect. Finally, we suggest that protons with energies higher than 636.18 keV can not be trapped by the compressional ULF wave efficiently due to the finite Larmor radius effect.
URLhttp://doi.wiley.com/10.1002/2016JA022706
DOI10.1002/2016JA022706
Short TitleJ. Geophys. Res. Space Physics


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