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Observations of kinetic scale field line resonances
Author(s) -
Chaston Christopher C.,
Bonnell John W.,
Wygant John R.,
Mozer Forrest,
Bale Stuart D.,
Kersten Kris,
Breneman Aaron W.,
Kletzing Craig A.,
Kurth William S.,
Hospodarsky George B.,
Smith Charles W.,
MacDonald Elizabeth A.
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2013gl058507
Subject(s) - physics , amplitude , excitation , magnetic field , magnetosphere , electric field , atomic physics , field line , computational physics , field (mathematics) , kinetic energy , field strength , alfvén wave , magnetohydrodynamics , optics , classical mechanics , mathematics , quantum mechanics , pure mathematics
Abstract We identify electromagnetic field variations from the Van Allen Probes which have the properties of Doppler shifted kinetic scale Alfvénic field line resonances. These variations are observed during injections of energetic plasmas into the inner magnetosphere. These waves have scale sizes perpendicular to the magnetic field which are determined to be of the order of an ion gyro‐radius ( ρ i ) and less. Cross‐spectral analysis of the electric and magnetic fields reveals phase transitions at frequencies correlated with enhancements and depressions in the ratio of the electric and magnetic fields. Modeling shows that these observations are consistent with the excitation of field‐line resonances over a broad range of wave numbers perpendicular to the magnetic field ( k ⊥ ) extending to k ⊥ ρ i ≫ 1. The amplitude of these waves is such that E / B o ≳ Ω i / k ⊥ ( E , B o , and Ω i are the wave amplitude, background field strength, and ion gyro‐frequency, respectively) leading to ion demagnetization and acceleration for multiple transitions through the wave potential.