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Fast Magnetosonic Waves Observed by Van Allen Probes: Testing Local Wave Excitation Mechanism
Author(s) -
Min Kyungguk,
Liu Kaijun,
Wang Xueyi,
Chen Lunjin,
Denton Richard E.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja024867
Subject(s) - physics , cyclotron , proton , computational physics , excited state , excitation , phase velocity , magnetic field , atomic physics , plasma , phase space , harmonics , distribution function , nuclear physics , optics , quantum mechanics , voltage
Linear Vlasov theory and particle‐in‐cell (PIC) simulations for electromagnetic fluctuations in a homogeneous, magnetized, and collisionless plasma are used to investigate a fast magnetosonic wave event observed by the Van Allen Probes. The fluctuating magnetic field observed exhibits a series of spectral peaks at harmonics of the proton cyclotron frequency Ω p and has a dominant compressional component, which can be classified as fast magnetosonic waves. Furthermore, the simultaneously observed proton phase space density exhibits positive slopes in the perpendicular velocity space, ∂ f p /∂ v ⊥ >0, which can be a source for these waves. Linear theory analyses and PIC simulations use plasma and field parameters measured in situ except that the modeled proton distribution is modified to have larger ∂ f p /∂ v ⊥ under the assumption that the observed distribution corresponds to a marginally stable state when the distribution has already been scattered by the excited waves. The results show that the positive slope is the source of the proton cyclotron harmonic waves at propagation quasi‐perpendicular to the background magnetic field, and as a result of interactions with the excited waves the evolving proton distribution progresses approximately toward the observed distribution.