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Van Allen Probes Observation of a Fundamental Poloidal Standing Alfvén Wave Event Related to Giant Pulsations
Author(s) -
Takahashi Kazue,
Claudepierre Seth G.,
Rankin Robert,
Mann Ian R.,
Smith Charles W.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2017ja025139
Subject(s) - physics , amplitude , equator , alfvén wave , spacecraft , proton , phase (matter) , standing wave , magnetic field , resonance (particle physics) , van allen probes , computational physics , atomic physics , magnetosphere , magnetohydrodynamics , optics , nuclear physics , van allen radiation belt , astronomy , latitude , quantum mechanics
The Van Allen Probes‐A spacecraft observed an ∼9‐mHz ultralow‐frequency wave on 6 October 2012, at L ∼ 5.7, in the dawn sector, and very near the magnetic equator. The wave had a strong electric field that was initially stronger in the azimuthal component and later in the radial component, exhibited properties of a fundamental standing Alfvén wave, and was associated with giant pulsations observed on the ground near the magnetic field footprint of the spacecraft. The wave was accompanied by oscillations of the flux of energetic protons ( j H+ ). The amplitude of log jH +oscillations was large at equatorial pitch angles away from 90°, and the energy dependence of the phase and amplitude of the oscillations exhibited features consistent with drift resonance of ∼140‐keV protons with a westward‐propagating wave having an azimuthal wave number of ∼−40. The wave was detected when the spacecraft entered a region of an earthward gradient of the proton phase space density, in support of a theoretical prediction that such a gradient can drive fundamental poloidal waves.