Pitch Angle Structures of Ring Current Ions Induced by Evolving Poloidal Ultra‐Low Frequency Waves

Autor: Z.‐Y. Liu, Q.‐G. Zong, X.‐Z. Zhou, Y.‐F. Zhu, S.‐J. Gu
Jazyk: angličtina
Rok vydání: 2020
Předmět:
Zdroj: Geophysical Research Letters, Vol 47, Iss 4, Pp n/a-n/a (2020)
Druh dokumentu: article
ISSN: 1944-8007
0094-8276
DOI: 10.1029/2020GL087203
Popis: Abstract 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.
Databáze: Directory of Open Access Journals
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