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Off‐Equatorial Source of Magnetosonic Waves Extending Above the Lower Hybrid Resonance Frequency in the Inner Magnetosphere
Author(s) -
Wu Zhiyong,
Su Zhenpeng,
Liu Nigang,
Gao Zhonglei,
Zheng Huinan,
Wang Yuming,
Wang Shui
Publication year - 2021
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 - 10.1029/2020gl091830
Subject(s) - plasmasphere , magnetosphere , physics , van allen radiation belt , van allen probes , geophysics , instability , computational physics , substorm , lower hybrid oscillation , equator , resonance (particle physics) , ring current , latitude , wave propagation , plasma , atomic physics , mechanics , optics , astronomy , nuclear physics , electromagnetic electron wave
Inner magnetospheric magnetosonic waves are usually considered to grow from the near‐equatorial ion Bernstein instability below the lower hybrid resonance frequency and contribute significantly to the radiation belt electron dynamics. We here present unusual observations of magnetosonic waves extending above the local lower hybrid resonance frequency in the midlatitude ∼15° plasmasphere after the substorm proton injection. Linear instability analyses and ray‐tracing simulations show that, because of the latitudinal variation of normal angles, these waves have little growth near the equator but are amplified accumulatively to the observable level over broad latitudes | λ | < 30° during the bounce‐drift propagation. Our data and modeling illustrate a previously unexplored scenario that off‐equatorial proton ring distributions could be a significant source of magnetosonic waves in the inner magnetosphere. Such off‐equatorially generated magnetosonic waves might differ from the near‐equatorially generated ones in latitudinal coverage, wavevector distribution, and then effect on the radiation belt electrons.