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Compressional ULF wave modulation of energetic particles in the inner magnetosphere
Author(s) -
Liu H.,
Zong Q.G.,
Zhou X.Z.,
Fu S. Y.,
Rankin R.,
Wang L.H.,
Yuan C. J.,
Wang Y. F.,
Baker D. N.,
Blake J. B.,
Kletzing C. A.
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja022706
Subject(s) - physics , magnetosphere , electron , atomic physics , gyroradius , range (aeronautics) , pitch angle , proton , radius , modulation (music) , charged particle , flux (metallurgy) , computational physics , ion , nuclear physics , plasma , geophysics , materials science , computer security , quantum mechanics , computer science , acoustics , metallurgy , composite material
We present Van Allen Probes observations of modulations in the flux of very energetic electrons up to a few MeV and protons between 1200 and 1400 UT on 19 February 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 cannot be trapped by the compressional ULF wave efficiently due to the finite Larmor radius effect.