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Pitch Angle Structures of Ring Current Ions Induced by Evolving Poloidal Ultra‐Low Frequency Waves
Author(s) -
Liu Z.Y.,
Zong Q.G.,
Zhou X.Z.,
Zhu Y.F.,
Gu S.J.
Publication year - 2020
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 - 10.1029/2020gl087203
Subject(s) - magnetosphere , physics , ring current , pitch angle , ion , resonance (particle physics) , oscillation (cell signaling) , van allen probes , computational physics , current (fluid) , flux (metallurgy) , atomic physics , geophysics , plasma , van allen radiation belt , materials science , quantum mechanics , biology , metallurgy , genetics , thermodynamics
Ultra‐low frequency (ULF) waves can effectively accelerate ring current ions through drift‐bounce resonance. Conventional theories have been developed to understand this resonance since the dawn of the space age, which usually assume ULF waves are quasi‐steady in time. However, ULF waves would experience growth and damping stages in the real magnetosphere, which requires an adjustment of the conventional theories. Here, we attempt to reveal how ions respond to evolving ULF waves. By analyzing an event observed by Van Allen Probe A and reproducing the observations via simulation, we find the phase shift of ion flux oscillation across resonant pitch angles varies with time, when wave growth and damping cannot be neglected. As a result, the inclination angle of stripes in pitch angle spectrogram varies with time, causing “fishbone‐like” pitch angle structures. One should take into account such ion behaviors when considering the role of drift‐bounce resonance in the real magnetosphere.