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Nonlinear Scattering of 90° Pitch Angle Electrons in the Outer Radiation Belt by Large‐Amplitude EMIC Waves
Author(s) -
Lee DaeYoung,
Kim KyungChan,
Choi CheongRim
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 - 10.1029/2019gl086738
Subject(s) - physics , electron , van allen radiation belt , pitch angle , scattering , cyclotron resonance , resonance (particle physics) , atomic physics , cyclotron , electromagnetic radiation , computational physics , magnetosphere , optics , geophysics , nuclear physics , plasma
Abstract Electromagnetic ion cyclotron (EMIC) waves can cause relativistic electron scattering and atmospheric precipitation, primarily via cyclotron resonant interactions in the Earth's radiation belts. However, the conventional quasilinear resonance theory suggests that the cyclotron resonance condition is not satisfied for 90° pitch angle (PA) electrons, which constitute the majority of electrons in the outer radiation belt, such that scattering mainly affects low‐PA electrons. In contrast to this theory, using test particle calculations, we demonstrate that even exactly 90° PA electrons can be significantly scattered by large‐amplitude EMIC waves. The finite wave force results in the parallel transport of 90° PA electrons away from the equator, corresponding to intrinsically nonresonant scattering. This can lead to parallel velocity that meets cyclotron resonance conditions as local PA deviates from 90°. Different types of resonance are identified depending on the wave normal angle, that is, first‐ and second‐order resonances for parallel and oblique waves, respectively.